An Investigation of the Thermal and Photochemical Reactions of
Ozone with Alkenes Using Matrix Isolation
A dissertation submitted to the
Graduate School
of the University of Cincinnati
in partial fulfillment of the requirements for the degree of
Doctorate of Philosophy
in the Department of Chemistry
of the College of Arts and Sciences
May 17, 2012
by
Bridgett Rakestraw (Coleman)
B.S., Chemistry, Ball State University, 2007
Chair: Dr. Bruce S. Ault
Abstract
The matrix isolation technique combined with infrared (IR) spectroscopy and theoretical
calculations has been used to investigate the thermal and photochemical reactions of ozone with
propene, 2,3-dimethyl-2-butene (DMB), styrene, and Z-3-methyl-2-pentene (MP). In the DMB
and styrene twin jet systems, upon annealing to 35 K and 68 K (respectively) several bands were
assigned to the primary ozonides, elusive Criegee intermediates, and secondary ozonides. The
twin jet annealed MP system yielded assignments to the primary and secondary ozonides. For
DMB, the wavelength dependence of the photo-destruction of these product bands was explored
with irradiation from λ ≥ 220 to ≥ 580 nm. A recently developed concentric jet method was also
utilized to increase yields and monitor the concentration of intermediates and products formed at
different times by varying the length of mixing distance (d = 0 to -11 cm) before reaching the
cold cell for spectroscopic detection. For the reaction of ozone with propene, initial twin jet
deposition upon annealing to 35 K yielded no visible changes in the IR spectra. Merged jet
deposition led to the observation of ‘‘later”, more stable products of this reaction for each alkene.
Irradiation of the twin jet systems for all alkenes in this study were dominated by ozone
decomposition and subsequent O atom reaction with the alkene. Identification of intermediates
and products formed during the ozonolysis of these alkenes were further supported by
18
O and
labeling experiments as well as theoretical density functional calculations at the B3LYP/6311G++(d,2p) level.
iii
iv
Acknowledgements
First and foremost, I would like to acknowledge God, because without Him I would not
be here to achieve the things I have.
To Dr. Ault, I am so grateful to have an advisor of your stature who is understanding and
genuinely wants me to succeed. I would like to acknowledge my committee members, Dr. Beck,
Pinhas and Smithrud for helpful discussions concerning my research. To my graduate school life
coaches, Dr. Gudmundsdottir and Dr. Mack, I am lucky to have had both of you during this time.
I would like to acknowledge my husband Ricky. Thank you for motivating and
supporting me every second from the beginning of this journey. Next, I want to express thanks
and love to my mother Pamela, and brother and sisters, Carlos, Jennifer, and Kiara, who have
always pushed me to exceed even my own expectations.
To everyone who has had a role in what I have accomplished over my time here, I thank
you.
Bridgett Rakestraw (Coleman)
May 2012
v
For my daughter, Emery
vi
Table of Contents
Page
iii
v
vi
vii
viii
x
Abstract
Acknowledgements
Dedication
Table of Contents
List of Figures
List of Tables
Chapter 1
Introduction to Tropospheric Chemistry, Criegee Mechanism for the
Ozonolysis of Alkenes and Matrix Isolation
1
Chapter 2
Experimental Methods
9
Chapter 3
Matrix Isolation Investigation of the Ozonolysis of Propene
17
Chapter 4
Investigation of the Thermal and Photochemical Reactions of
Ozone with 2,3-dimethyl-2-butene
30
Chapter 5
Investigation of the Thermal and Photochemical Reactions of
Ozone with Styrene in Argon and Krypton Matrices
50
Chapter 6
Ozonolysis of Z-3-methyl-2-pentene Using Matrix Isolation
Infrared Spectroscopy
65
Chapter 7
Theoretical Relative Energies for the Intermediates from
the Ozonolysis of Alkenes
78
Chapter 8
Overall Conclusions and Future Work
85
Appendix A
Supporting information for Chapter 4
86
Appendix B
Supporting information for Chapter 5
97
Appendix C
Supporting information for Chapter 6
105
Addendum
Alternate Route to the Criegee Intermediate
109
vii
List of Figures
Figure
Description
Page
1.1
Criegee mechanism for the ozonolysis of alkenes.
2.1
Three modes of deposition.
11
2.2
Sample preparation manifold.
12
3.1
Infrared spectrum of a matrix formed by the merged jet (2 m) deposition
of a sample of Ar/ozone = 250 with a sample of Ar/propene = 250 and annealed
to 35K.
19
3.2
Infrared spectra of a matrix formed by the twin jet deposition of a sample of
Ar/ozone = 250 with a sample of Ar/propene = 250 and annealed to 35K. The
upper trace is before irradiation, while the lower trace is after 1.0 h of irradiation
with light of λ ≥ 220 nm.
19
3.3
Calculated structures for the (a) primary ozonide, (b) Criegee intermediate 1,
(c) Criegee intermediate 2, and (d-f) secondary ozonides 1, 2, and 3 from the
reaction of ozone with propene.
23
3.4
Calculated structures for (a) epoxypropane, (b) propanal, and (c) acetone from
the photochemical reaction of ozone with propene.
23
3.5
Scheme for the O atom attack on the double bond of propene.
25
4.1
Select region of IR spectra from twin jet deposited Ar:16O3:DMB = 500:1:1.
Black trace is after 19 hrs of depositing. Blue trace is after annealing to 35K.
33
4.2
IR spectra of twin jet deposited O2:O3:DMB = 500:1:1. Blue trace is after
depositing for 19 h. Black trace is the result after irradiating with  ≥ 220nm
for 1 h.
33
4.3
Calculated structures for the (a) primary ozonide, (b) Criegee intermediate, and
(c) secondary ozonide from the reaction of ozone with DMB.
37
4.4
Scheme for the O atom attack on the double bond of DMB.
43
4.5
IR spectra of twin deposited Ar:16O3:DMB = 500:1:1. Black trace is spectrum
upon annealing to 35K. Blue trace is upon irradiating with  ≥ 220 nm.
45
viii
3
5.1
C=O stretch region of the infrared spectrum of a matrix formed by the twin jet
deposition of a sample of Ar:16O3 = 250 with a sample of Ar:Styrene = 250
annealed to 35K and irradiated with λ ≥ 220 nm for 1 h. Blue trace is before
irradiation and red trace is after irradiation. New product bands are labeled in blue.
52
5.2
The lower red trace is the infrared spectra of a matrix formed by the twin jet
deposition of a sample of Kr:16O3 = 250 with a sample of Kr:Styrene = 250
upon annealing to 68 K. The labeled bands are those that grew upon annealing.
The upper trace is the same experiment, however with 18O labeling.
53
5.3
Calculated structures for the (a) primary ozonide, (b)
benzaldehyde-O-oxide Criegee intermediate, (c) formaldehyde-O-oxide
Criegee intermediate and (d) a possible secondary ozonide from the reaction
of ozone with styrene.
56
6.1
Red trace is the spectrum resulting from the twin jet Ar:O3:MP = 2000:4:5 annealed
to 35 K. Bands that grew in upon annealing are labeled. The blue trace spectrum is
Ar:MP = 200:1 upon annealing to 35K.
66
6.2
C=O stretch region. Lower trace: twin jet annealed Ar:O3:MP = 2000:4:5. Upper
trace is the result upon irradiation for 1 h at λ ≥ 220 nm.
69
6.3
Possible intermediates resulting from the ozonolysis of MP. (a) primary ozonide,
(b) acetaldehyde-O-oxide, (c) butanone-O-oxide, (d) secondary ozonide.
69
6.4
Black trace shows select region of a merged jet (1 m) Ar: 2000:4:5 experiment.
Blue trace is an Ar: MP = 200:1 blank.
71
7.1
Intermediates from the ozonolysis of propene.
78
7.2
Intermediates from the ozonolysis of 2,3-dimethyl-2-butene.
79
7.3
Intermediates from the ozonolysis of styrene.
80
7.4
Intermediates from the ozonolysis of Z-3-methyl-2-pentene.
82
ix
List of Tables
Table
Description
Page
3.1
Product Bands from the Merged Jet (2m) Deposition of Ozone with Propene.
20
3.2
Band Positions and Assignments for New Product Absorptions from the
Twin Jet Deposition of Ozone with Propene upon Irradiation with Light
of λ ≥ 220 nm.
21
3.3
Calculated IR data for the Intermediates from the Ozonolysis of Propene.
24
4.1
Band Positions and Assignments for the Initial Intermediates in the Thermal
Reaction of O3 with DMB.
32
4.2
Band Positions and Assignments for New Product Absorptions from the
Twin Jet Deposition of Ozone with DMB upon Irradiation with Light
of λ ≥ 220 nm.
34
4.3
Product Band Positions and Assignments for the Intermediates in the Ozonolysis
of DMB.
37
5.1
Band Assignments from Twin Jet Ar:Ozone:Styrene Irradiated Experiment.
52
5.2
Band Assignments from Twin Jet Kr:O3:Styrene Annealed to 68 K.
54
5.3
Ar:Ozone:Styrene Merged Jet Product Assignments and Behavior Upon Irradiation.
56
6.1
Intermediate Bands From the Twin Jet Annealed Ar:O3:MP=2000:4:5.
68
6.2
New Bands Resulting from the Twin Jet Photolysis of Ar:O3:MP=2000:4:5.
70
7.1
Relative Zero Point Energies for the Intermediates in the Ozonolysis of Propene.
78
7.2
Relative Zero Point Energies for the Intermediates in the Ozonolysis of
2,3-dimethyl-2-butene.
79
7.3
Relative Zero Point Energies for the Intermediates in the Ozonolysis of Styrene
7.4
Relative Zero Point Energies for the Intermediates in the Ozonolysis of
Z-3-methyl-2-pentene.
83
7.5
Benchmark Calculations for C=O Stretch 18O Isotopic Shifts
Compared to Experimental Values.
84
x
.
81
Chapter 1
Introduction to Tropospheric Chemistry, Criegee Mechanism for the Ozonolysis of Alkenes
and Matrix Isolation
This dissertation will mostly focus on the thermal and photochemical reactions between a
variety of simple alkenes and ozone. Ozone (O3) is a highly reactive allotrope of atmospheric
oxygen in which the molecule is composed of three, rather than two, oxygen atoms. 1 Like many
other natural occurring molecules, ozone has both beneficial and harmful effects on humans and
the environment. On the positive side, the ozone layer in the Earth’s stratosphere (10 to 30 miles
above Earth) protects us from the sun’s dangerous rays. In contrast, ground level or tropospheric
ozone has damaging environmental and health effects such as loss of vegetation/ecosystems and
the reduction of lung function in children, elderly, and outdoor workers to name a few.2
According to the United States Environmental Protection Agency, ground-level or “bad” ozone
is not emitted directly into the air, but is created by chemical reactions between oxides of
nitrogen (NOx) and volatile organic compounds (VOCs) in the presence of sunlight, mostly from
anthropogenic sources.2 While humans are able to reduce the emissions of NOxs and VOCs by
adopting an environmentally friendly lifestyle, there is also an anthropogenic impact on
tropospheric self cleansing.3 It is clear that O3 does not react appreciably with alkanes in the
troposphere (as OH radical does)4; however, it plays a significant role in the oxidation/removal
of alkenes which arise from both biogenic and anthropogenic sources. Another significant
feature to note is that many of these natural atmospheric conversions are driven, directly or
indirectly, by solar ultraviolet (UV) radiation. Thus, the photochemistry between an O atom
(from the photo-decomposition of O3) and alkenes is explored as well. Moreover, an important
goal is to understand the sources of different trace gases as well as their removal mechanisms,
i.e. their atmospheric budget.
1
The importance of the reaction of O3 with alkenes in the troposphere has led to many
experimental and theoretical studies of the kinetics and mechanism of this reaction. Early work
done by Rudolf Criegee yielded a proposed mechanism (Figure 1.1) for the ozonolysis of
alkenes.5,6 Through vigorous experimental and theoretical evidence, this mechanism is now
widely accepted.7-10 The mechanism involves the initial formation of a primary ozonide by a 1,3
polar addition across the double bond of the alkene, forming a 1,2,3-trioxolane species. This
reaction is quite exothermic, leading to further reaction and decomposition into an aldehyde and
the proposed Criegee intermediate, a carbonyl oxide. The Criegee intermediate and the aldehyde
may then recombine to form a secondary ozonide (1,2,4-trioxolane), or react further to form a
range of products.
Although experimental and theoretical studies involving the isolation of the secondary
ozonide for numerous systems have supported this mechanism, the primary ozonide and Criegee
intermediate have just recently been isolated for a small number of alkenes.11-14 On the other
hand, theoretical calculations have provided insight into the nature of the ozonolysis reaction as
well as to the reasons for the difficulties in observing the Criegee intermediate under normal
laboratory conditions.7-10 Theoretical studies have shown that the activation barrier connecting
the primary ozonide to the Criegee intermediate is about 19 kcal/mol. The primary ozonide is
formed with nearly 50 kcal/mol excess energy and it can easily continue over the barrier to form
the Criegee intermediate and carbonyl compound. This pair will also be formed with excess
energy, and must either be quickly deactivated and stabilized, or they will react further to form
the numerous known products. One pathway to stabilization is ring formation, yielding the
secondary ozonide, a 1,2,4-trioxolane.
2
Figure 1.1 Criegee mechanism for the ozonolysis of alkenes.
3
One way to dissipate excess energy in this reaction is through substituents on the alkene.
A theoretical study by Cremer and co-workers concluded that the more vibrational degrees of
freedom an alkene possesses, the higher a resulting intermediate’s chance to stabilize before a
subsequent reaction.15 Also, Atkinson explored the kinetics for the overall reaction and
established a trend that relates effects of substituent identity, number, and orientation about the
carbon-carbon double bond on room temperature rate constants for this reaction.16 Methyl groups
(1, 2, 3 or 4) enhance the rate constant appreciably, while halogens decrease the room
temperature rate constant. These models served as a guide for the selection of alkenes examined
in this work. The rate constants at ~298K for the reaction between ozone and the alkenes studied
here are as follows: propene 6.80 x 106, 2,3-dimethyl-2-butene (DMB) 6.99 x108, styrene 1.30 x
107, Z-3-methyl-2-pentene (MP) 2.75 x 108, all in units cm3 mol-1 s-1.16
The matrix isolation technique is an attempt to overcome the difficulties associated with
reactive intermediates such as those formed in the Criegee mechanism. This method involves
trapping a reaction in a rigid cage of a chemically inert substance (a matrix) at a low temperature.
More specifically, the species under study here are diluted in excess of an inert gas (usually
argon), with dilution ratios between 100:1 and 1000:1. At 10-21 K (achieved by a high vacuum
and cryogenic refrigerator), the gas mixture forms a solid lattice and the reaction is trapped
(species are “caged paired”). The rigidity of the cage prevents diffusion of reactive molecules
that would lead to bimolecular collisions.17
The nature of the matrix, the low temperature and the need to isolate the sample in a high
vacuum all imply that only spectroscopic methods that allow monitoring of the sample during
cooling can be used to characterize matrix isolated species.18 Fourier transform infrared
spectroscopy (FT-IR) is the main spectroscopic method used in this work. It is important to give
4
some consideration to the spectroscopic effects which the matrix host will have on the guest
species (generated in the gas phase). With limited diffusion and rotation, a matrix absorption
lacks rotational fine structure and IR bands are narrow (<1 cm-1), which reduces band overlap
and enhances spectra analysis. In contrast, variable interaction between host and guest species
can cause site splitting and arises when a trapped guest species occupies matrix cages of different
sizes. This often results in band broadening, however, and can be minimized at sufficient high
dilution ratios.
The major goal in this study is to capture the anticipated intermediates formed via the
Criegee mechanism for the ozonolysis of propene, 2,3-dimethyl-2-butene (DMB), styrene, and
Z-3-methyl-2-pentene (MP). The characterization of these intermediates will support the Criegee
mechanism and contribute to the knowledge of tropospheric chemistry. Since the conditions of
the matrix require that samples are generated in the gas phase, propene was chosen as a starting
point and is a gas at room temperature. Based on the structure activity relationship Atkinson
established, the tetra methyl substituted DMB was studied.16 The benzaldehyde-O-oxide Criegee
intermediate has a known IR spectrum (not from the ozonolysis of styrene) and served as the
premise for investigating the ozonolysis of styrene. The study involving MP is an attempt to
reproduce the aforementioned studies and to investigate the conformers of the Criegee
intermediate using calculations. Subsequently, the photo-decomposition of these species is also
explored. Matrix isolation coupled to FT-IR spectroscopy and theoretical calculations are used to
isolate and characterize the reaction intermediates and final products. A brief summary of this
investigation is as follows: Chapter 2 is a detailed description of the matrix isolation
experimental technique covering three modes of deposition (twin, merged, and concentric jet),
photolysis procedure and isotopic labeling. The sample preparation method for each species will
5
be described as well as detail into the theoretical technique used to compliment the experimental
study. Chapter 3 will cover the thermal reaction between O3 and propene, but will focus on the O
atom photochemistry for this system. In Chapter 4, the thermal and photochemical reaction
between O3 and 2,3-dimethyl-2-butene is explored. Chapter 5 covers the thermal and
photochemical reactions of O3 with styrene in argon and krypton matrices. Chapter 6 is the
investigation of the thermal and photochemical reactions of O3 and Z-3-methyl-2-pentene.
Detailed theoretical work is listed in Chapter 7 and conclusions are in Chapter 8.
6
References:
(1)
Bailey, P. Ozonation in Organic Chemistry Olefinic Compounds; Academic Press, Inc.:
New York, 1978.
(2)
U.S. Environmental Protection Agency. Ozone: Good Up High, Bad Nearby.
Washington: Government Printing Office, 2003.
(3)
Holloway, A.M.; Wayne, R.P. Atmospheric Chemistry RSC Publishing: Cambridge,
2010.
(4)
Barker, J. R. Progress and Problems in Atmospheric Chemistry, Advanced Series in
Physical Chemistry Vol. 3; World Scientific Publishing Co.: New Jersey, 1995.
(5)
Criegee, R. Rec. Chem. Prog. 1957, 18, 111.
(6)
Criegee, R. Angew. Chem. 1975, 87, 765.
(7)
Chan, W.-T.; Hamilton, I. P. J. Chem. Phys. 2003, 118, 1688–1701.
(8)
Hendricks, M. F. A.; Vinckier, C. J. Chem. Phys. A 2003, 107, 7574–7580.
(9)
Ljubic, I.; Sabljic, A. J. Phys. Chem. A 2002, 106, 4745–4757.
(10)
Anglada, J. M.; Crehuet, R.; Bofill, J. M. Chem. Eur. J. 1999, 5, 1809–1822.
(11)
Hoops, M. D.; Ault, B. S. J. Am. Chem. Soc. 2009, 929, 22.
(12)
Clay, M.; Ault, B. S. J. Phys. Chem. A 2010, 114, 2799-2805.
(13)
Coleman, B. E.; Ault, B. S. J. Phys. Chem. A. 2010, 114, 12667–12674.
(14)
Coleman, B. E.; Ault, B. S. J. Mol. Struc. 2012, in press.
(15)
Wierlacher, S.; Sander, W.; Marquardt, C.; Kraka, E.; Cremer, D. Chem. Phys. Lett.
1994, 222, 319.
(16)
Atkinson, R.; Carter, W. Chem. Rev. 1984, 84, 437-470.
(17)
Dunkin, I. R. Matrix Isolation Techniques; Oxford University: Oxford, 1998.
7
(18)
Cradock, S.; Hinchcliffe, A. J. Matrix Isolation; Cambridge University Press: Cambridge,
1975.
8
Chapter 2
Experimental Methods
Matrix isolation apparatus:
All of the experiments in this study were carried out on a conventional matrix isolation
apparatus.1 The experimental setup consists of a closed cycle helium refrigeration system with
cold head apparatus, sample cell, infrared spectrometer, mechanical and diffusion pumps, and
sample preparation manifolds.
The low temperatures (10-21 K) were achieved with a Cryodyne refrigeration system.
The system consists of a Model 8300 Compressor, a Model 8001 Controller, and a Model 22
Cold Head refrigerator. The compressor is connected to the cold head refrigerator by stainless
steel interconnecting lines. The cold head shaft is insulated by a threaded-on aluminum radiation
shield. A copper window holder is mounted on the end of the cold head refrigerator. A CsI
window is sandwiched between two sections of the holder and tightened with screws. The
temperature is monitored by a silicon diode sensor, also bolted onto the end of the cold head
refrigerator. Annealing (to 35 and 68 K) is achieved by a 20W button heater mounted on the
edge of the copper window holder and was controlled by a variac. Indium gaskets are used to
maximize thermal contact between each interface.
The cold head is enclosed in a cylindrical aluminum vacuum shroud attached to a cubical
sample cell. The sample cell is composed of five O-ring sealed threaded openings and a larger
top O-ring sealed opening. With the top opening sealed by the cold head vacuum shroud, CsI
windows are thread-mounted on four adjacent sides and a glass window on the bottom. On the
vertical edges of the sample cells are Swagelok O-ring fitted inlets for the different jet deposition
9
modes. In Figure 2.1a, there are two adjacent inlets with a ⅛ in. fitting for the twin jet mode. In
Figure 2.1b and c there is a ¼ in. fitting for merged and concentric jet modes.
A high vacuum (10-7 torr) is achieved by connecting Welch rotary pump and a Varian M2 diffusion pump to the vacuum shroud. The vacuum is maintained in two stages, first by
pumping on the cold head apparatus with the rotary pump monitored by a Varian thermocouple
gauge (2000 to 10 mtorr), then switching to the diffusion pump (also backed by the rotary
pump), and monitoring the sample cell pressure using a Varian cold cathode gauge (10-3 to 10-7
torr).
The gaseous samples were prepared in two separate ¼ in. o.d. stainless steel manifolds
connected to the sample cell using Nupro needle valves (Figure 2.2). Each manifold is composed
of an Ashcroft Duragauge that measures the pressures during sample preparation in units of
inches of mercury. The manifolds are each equipped with a cold finger, 2L stainless steel can,
and a single argon cylinder (shared between the two manifolds). In addition, on the side
traditionally used to generate ozone, one manifold was connected to an oxygen cylinder. The
opposite manifold often had the cold finger removed and was replaced with a lecture bottle
containing the desired compound. Each connection is controlled using Nupro or Swagelok valves
and sealed with Swagelok fittings. There was also a copper line that connected the two manifolds
to the rotary pump. In each experiment, the samples were generated in the gas phase, diluted in
argon to the desired concentration, and stored in the stainless steel can until the sample cell was
cooled to 10-21 K. Then the diluted samples were deposited through the needle valve using the
desired mode of deposition.
Matrix samples were deposited using ⅛ and ¼ in. o.d. Teflon FEP tubing in the twin,
merged and concentric jet modes. In the first, the two gas samples were deposited from separate
10
CsI windows
IR beam
Cu window
mount
a)
b)
c)
Figure 2.1 Three modes of deposition; a) twin, b) merged, c) concentric jets.
11
Figure 2.2 Sample preparation manifold.
12
⅛ in. nozzles onto the 19 K window, allowing for only a very brief mixing time prior to matrix
deposition. Several of these matrices were subsequently warmed or annealed to 35 (or 68K in Kr
matrices) to permit limited diffusion and/or reaction of unpaired starting materials. These
matrices were then recooled to 19 K and additional spectra recorded. In addition, the twin jet
matrices were irradiated for 1.0 h with the H2O/quartz-filtered output of a 200 W mediumpressure Hg arc lamp, after which further spectra were recorded. Using a variety of coated quartz
filters, a number of the twin jet experiments were irradiated with wavelengths ranging from  ≥
220 nm to ≥ 580 nm. Ozone dissociates at  ≥ 220 nm to diatomic oxygen and an O atom
achieving a photo-reaction with the alkene.
Many experiments were conducted in the merged jet mode, in which the two ¼ in. o.d.
deposition tubes were joined with an UltraTorr tee to a third ¼ in. o.d. tube at a predetermined
distance from the cryogenic surface, and the flowing gas samples were permitted to mix and
react during passage through the (third tube) merged region. The length of this region ranged
from 0.5 m to 2.0 m in length for this study.
Twin and merged jet deposition probe different time scales for reaction, very short for
twin jet and somewhat longer for merged jet. To probe the intermediate time scale between twin
and merged jet, a new concentric jet device was developed. In this approach, an ⅛ in. o.d. Teflon
FEP tube was inserted inside of a larger, ¼ in. o.d. tube, also Teflon FEP. The length of the ⅛ in.
tube could be adjusted to be shorter, longer, or the same as the outer tube. The distance between
the outlet ends of the two tubes is referred to as Δd = (position of inner tube) − (position of outer
tube). d > 0 indicates that the inner tube extends beyond the outer tube (more like twin jet), and d
< 0 indicates that the inner tube is shorter than the outer tube (more like merged jet). d = 0
indicates that the ends of the two tubes are at the same distance from the cold window. Mixing of
13
the two samples begins at the outlet of the inner tube and continues until deposition onto the cold
window (typically 2-3 cm). In this manner, the time scale available for reaction could be adjusted
from nearly that of the merged jet to nearly that of twin jet. In all three modes, matrices were
deposited at the rate of 2 mmol/h from each sample manifold onto the cold window. Final
spectra were recorded on a Perkin-Elmer Spectrum One FT-infrared (IR) spectrometer at 1 cm-1
resolution.
Reagents:
Propene (Matheson, 99%) was introduced as a gas from a lecture bottle and purified by
freeze–pump–thaw cycles at 77 K. Styrene (Aldrich, 99%), 2,3-dimethyl-2-butene (DMB)
(Acros, 98%) and Z-3-methyl-2-butene (Aldrich, 97%) were introduced into the vacuum system
as the vapor above the room temperature liquid, after purification by freeze-pump-thaw cycles at
77 K.
Ozone-16O was produced by tesla coil discharge of 16O2 (Wright Brothers) and trapping at
77 K to remove residual 16O2 and trace gases. Ozone-18O was produced in the same manner using
oxygen-18O (Cambridge Isotope Laboratories, 94%). Oxygen-18O labeling of ozone will ideally
result in oxygen-18O labled intermediates. Using IR spectroscopy, there is an observable red shift
in oxygen-18O containing vibrations when compared to an oxygen-16O species of the same
vibration. This is useful when making assignments to intermediate structures.
Hydroxyacetone (Aldrich 90%), acetaldehyde (Aldrich, 99%), benzaldehyde (Aldrich,
99%), and acetone (Aldrich, 99%) in blank experiments were introduced into the vacuum system
as the vapor above the room temperature liquid, after purification by freeze-pump-thaw cycles at
77 K.
14
Argon, oxygen, and krypton (Wright Brothers) were used as the matrix gases without
further purification.
Theoretical Calculations
Theoretical calculations were carried out on starting materials, possible intermediates and
final products in this study, using Gaussian 03 and 03W suite of programs2 Density functional
calculations using the hybrid B3LYP functional were used to locate energy minima, determine
structures, and calculate vibrational spectra. Final calculations with full geometry optimization
employed the 6-311G++(d,2p) basis set, after initial calculations with smaller basis sets were run
to approximately locate energy minima. Transition states were confirmed by an IRC calculation
and optimizations of begin, saddle, and end points. Assignments of experimental bands were
based on correlations with theoretical data, behavior upon annealing and photolysis, as well as
literature spectra.
15
References:
(1)
Ault, B. S. J. Am. Chem. Soc. 1978, 100, 2426.
(2)
Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman,
J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S.
S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.;
Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.;
Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador,
P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.;
Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul,
A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara,
A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.;
Pople, J. A. Gaussian 03, revision B.04; Gaussian, Inc.: Pittsburgh, PA, 2003.
16
Chapter 3
Matrix Isolation Investigation of the Ozonolysis of Propene
Introduction
Propene is an asymmetric alkene that would form asymmetric primary ozonide (POZ)
upon ozonolysis following the Criegee mechanism. The primary ozonide, having one substituent,
can decompose in two separate directions forming two Criegee intermediate (CI), aldehyde pairs.
If able to diffuse, these pairs can combine to form several cross secondary ozonides (SOZ).
Propene is also known to have a relatively low rate constant for reaction with ozone at room
temperature (when compared to more highly substituted alkenes). The present experiments serve
as a preliminary measure for the behavior of the more reactive systems under matrix conditions.
As a result, this study has led to the observation of several late, stable products for the ozonolysis
reaction with propene.
Results
Prior to any deposition experiments, blank experiments were run on each of the reagents
used in this study.1,2 Acetaldehyde and acetone blank spectra were also obtained for comparison
with experimental spectra. In each case, the blanks were in good agreement with literature
spectra.3,4
Merged Jet
16
O3 + Propene. Initial merged jet experiments were conducted with samples of
Ar/ozone = 250 and Ar/propene = 250, using a 2.0 m merged or reaction region, at room
temperature. These concentrations yielded well resolved IR bands for each starting material. This
configuration allows for increased gas phase reaction time for the reactions relative to twin jet
deposition prior to matrix deposition. In each of the merged jet experiments, the parent bands of
both reagents were substantially reduced in intensity, indicating that a reaction was occurring. In
17
addition, many new product bands were observed throughout the spectrum, including several
intense bands in the carbonyl stretching region that grew slightly upon annealing to 35K. Figure
3.1 shows portions of the spectrum from one merged jet experiment and bands are listed in Table
3.1. These bands were reproduced in several experiments, all with the merged region held at
room temperature. For a number of experiments, the merged jet flow reactor length was varied
ranging from 0.5 m to 2.0 m. As a result, all product absorptions increased when going from the
0.5 m length to 2.0 m. Also, additional merged jet experiments were conducted, varying both
reactants from M/R (matrix/reactant) = 167 to M/R = 500. These experiments provided a
deviation in product concentration without compromising dilution ratios and subsequent
secondary reactions. Changes in product absorptions were directly proportional to the variation
of reactant concentrations.
Twin Jet
16
O3 + Propene. A series of twin jet experiments were conducted with samples of
Ar/ozone = 250 and Ar/propene = 250. After 19.0 h of deposition no product bands were
observed. This matrix was annealed to 35 K and recooled to 19 K. A spectrum was then
recorded, and no changes were noted. This was repeated numerous times varying both reactant
concentrations with no new product band observation. This matrix was then irradiated for 1.0 h
with the filtered (λ ≥ 220 nm) output of a medium-pressure Hg arc lamp. This produced many
new product bands, as listed in Table 3.2 and Figure 3.2 shows a representative region of this
spectrum. This experiment was repeated several times, using different sample concentrations.
The results were reproducible, with product band intensities that varied proportional with sample
concentrations.
18
O3 + Propene. Merged jet experiments were also conducted with samples of Ar/18O3 = 250
deposited with samples of Ar/propene = 250 and the outcomes were comparative to the normal
18
*
0.80
0.76
0.72
Intensity
*
*
0.68
*
0.64
0.60
0.56
*
0.52
1790
1780
1770
1760
1740
1750
1730
1720
1710
-1
Wavenumbers (cm )
Figure 3.1 Infrared spectrum of a matrix formed by the merged jet (2 m) deposition of a sample
of Ar/ozone = 250 with a sample of Ar/propene = 250 and annealed to 35K. New product bands
are marked with an asterisk.
0.50
0.40
Intensity
0.30
0.20
0.10
0.00
-0.10
-0.20
2200
2000
1900
1800
1700
1600
1500
-1
Wavenumbers (cm )
Figure 3.2 Infrared spectra of a matrix formed by the twin jet deposition of a sample of Ar/ozone
= 250 with a sample of Ar/propene = 250 and annealed to 35K. The upper blue trace is before
irradiation, while the lower red trace is after 1.0 h of irradiation with light of λ ≥ 220 nm.
19
Table 3.1 Product Bands from the Merged Jet (2 m) Deposition of Ozone with Propene
ν16O - ν18O
exp bandsa
calcd bandsb
calcd shift
exp shift
assignment
1117
1083
-34
acetaldehyde
1135
1110
-21
-25
formic acid
1245
1241
-5
-4
formaldehyde
1349
1348
0
-1
acetaldehyde
1362
1362
-6
0
acetaldehyde
1427
1425
-1
-2
acetaldehyde
1470
1471
0
1
acetic acid
1497
1488
-9
-9
formaldehyde
1728
1706
-36
-22
acetaldehyde
1740
1701
-37
-39
formaldehyde
1752
1718
-34
acetaldehyde
1762
1729
-37
-33
formic acid
1776
1744
-35
-32
acetic acid
formic / acetic
3528
3520
-12
-8
acid
a
-1 b
Frequencies in cm . Calculated at B3LYP/6-311G++(d,2p). Theoretical error
±3%. Experimental error ≤ ±1 cm-1.
20
Table 3.2 Band Positions and Assignments for New Product Absorptions from the Twin Jet
Deposition of Ozone with Propene upon Irradiation with Light of λ ≥ 220 nm
ν16O - ν18O
exptl bandsa
literature bandsb
calcd bandsc
calcd shifts
exptl shifts
assignment
743
742
767
-10
0
epoxypropane
828
827
838
-15
-13
epoxypropane
850
866
874
0
-5
propanal
950
949
971
-9
-8
epoxypropane
1028
1030
1040
-1
-3
epoxypropane
1095
1092
1118
-1
0
acetone
1223
1223
1233
-1
-5
acetone
1268
1267
1260
-4
-8
epoxypropane
1349
1353
1388
0
-11
acetone
1362
1361
1389
0
0
acetone
1393
1465*
1465
0
-5
acetone
1409
1410
1407
0
0
epoxypropane
1418
1413
1469
0
0
acetone
1429
1428
1475
-2
0
acetone
1499
1498
1532
-9
-12
formaldehyde
1700
1700*
-24
acetone
1722
1720
1785
-34
-23
acetone
1735
1727
1802
-36
-19
propanal
a
-1 b
c
Frequencies in cm . Refs. 4, 12, and 13. Calculated at B3LYP/6-311G++(d,2p).
Theoretical error ±3%. Experimental error ≤ ±1 cm-1. *Bands observed in blank acetone IR
spectrum in Ar matrix.
21
isotope of ozone. Many product bands were red shifted, some of which were slightly less intense,
while the parent bands were reduced greatly. Twin jet experiments were conducted with these
reagents, with results paralleling these obtained for the normal isotopic species. No new product
bands were observed upon initial deposition or annealing. With irradiation of the twin jet
experiment, shifted absorptions were observed.
Results of Calculations
The variety of experimental approaches in these studies resulted in several potential
products. In the merged jet experiments, possible products are known species for which literature
spectra are available for comparison. Although the anticipated intermediates originally proposed
by Criegee, (i.e. the primary ozonide, Criegee intermediate, and secondary ozonide) were
ultimately not detected in any of these experiments, they were also considered as they provide
the purpose for studying these ozonolysis reactions. Since literature spectra are not available for
comparison for these intermediates, the structures, and vibrational spectra including 18O isotopic
shifts for the propene system were calculated using DFT methods, the B3LYP hybrid functional,
and basis sets as high as 6-311G++(d,2p). The structures in Figure 3.3 serve as calculated
representations of possible intermediates for this system. All of the vibrational fundamentals
(unscaled) of these “early” intermediates are listed in Table 3.3. Similar calculations for the final
photochemical products were also studied and compared to known literature spectra in the
literature. Figure 3.4 represents the photochemical products from the twin jet experiments.
Discussion
Following the Criegee mechanism for the ozonolysis of propene in Figure 3.3, the
primary ozonide (a) will decompose in two ways to form acetaldehyde with a formaldehyde-like
Criegee intermediate (c) as well as formaldehyde with an acetaldehyde-like Criegee intermediate
22
(a)
(b)
(c)
(d)
(e)
(f)
)
Figure 3.3 Calculated structures for the (a) primary ozonide, (b) Criegee intermediate 1, (c)
Criegee intermediate 2, and (d-f) secondary ozonides 1, 2, and 3 from the reaction of ozone with
propene.
(a)
(b)
(c)
Figure 3.4 Calculated structures for (a) epoxypropane, (b) propanal, and (c) acetone from the
photochemical reaction of ozone with propene.
23
Table 3.3 Calculateda IR data for the Intermediates from the Ozonolysis of Propene
POZ
CI1
CI2
SOZ1
SOZ2
SOZ3
freq
int
freq
int
freq
int
freq
int
freq
int
freq
int
242
0
257
0
668
5
232
0
376
8
199
4
316
3
324
11
900
107
299
9
710
2
225
0
386
3
553
9
942
39
397
4
749
1
231
0
481
7
863
12
1245
17
489
9
843
13
324
0
662
12
887
37
1403
16
715
1
925
8
396
2
703
16
964
103
1535
30
749
3
951
80
499
22
733
19
1067
0
3115
4
833
4
1035
30
508
2
833
9
1162
6
3268
1
850
11
1086 181
724
0
895
5
1356
13
888
27
1140
10
756
1
927
3
1429
16
961
45
1143
0
826
5
953
1
1473
14
1056
38
1222
4
850
4
998
35
1478
14
1072
35
1227
4
855
11
1061
16
1580
1
1120 189 1373
6
901
38
1108
4
3025
5
1140
14
1415
8
923
17
1164
1
3068
5
1150
9
1517
1
1053
1
1244
1
3139
2
1234
4
1527
0
1083
43
1308
0
3155
7
1306
7
3022 130 1099
1
1343
1
1384
14
3024
0
1127 295
1379
9
1399
8
3104
32
1143
24
1414
13
1414
41
3105
0
1144
0
1490
6
1487
5
1288
3
1500
6
1490
4
1338
15
1507
2
1518
1
1376
33
3028
5
3014
77
1386
2
3035
38
3040
8
1411
76
3068
7
3051
22
1414
1
3093
16
3108
14
1486
10
3112
11
3110
12
1488
0
3118
20
3124
14
1490
1
1493
7
3040
19
3040
0
3055
37
3059
1
3107
5
3107
23
a
-1
Calculated at the B3LYP/6-311G++(d,2p) level. Frequencies in cm . Intensities in km mol-1.
Theoretical error ±3%.
24
Figure 3.5 Scheme for the O atom attack on the double bond of propene.
25
(b). These two pairs can combine in three ways to form three cross secondary ozonides (d-f) in
Figure 3.3. In our merged jet experiments for the ozone/propene system, parent bands decreased
with the result of new product absorptions, showing that extensive reaction had occurred. In
particular were numerous bands in the carbonyl stretch region as well as an absorption at 3528
cm-1 with an
18
O shift of -8 cm-1, strongly suggesting the formation of a carboxylic acid. A
related gas phase study5 of the reaction of propene with ozone at room temperature in a static
system with rapid mixing, yielded acetaldehyde and formaldehyde as major products and minute
amounts of acetic and formic acid. Specific product identifications can be made from known
literature spectra for acetaldehyde, acetic acid, formaldehyde, and formic acid in these
experiments.3,6-8 Although only stable products were formed, some can be seen as a result of the
primary Criegee mechanism and secondary reactions (stabilization of the Criegee intermediate).
The presence of both formaldehyde and acetaldehyde for this system is consistent with the
proposed Criegee mechanism. However, in this case it appears that the two Criegee
intermediates may have very quickly rearranged to form acetic and formic acid instead of the
combining with the aldehydes to form cross secondary ozonides. This observation is known to
result in experiments with longer mixing times.5 Spectral evidence did not support formation of
any other products or intermediates for the merged jet system. Not only do these results give
evidence for the Criegee mechanism, but most important, the formation and rearrangement of the
long sought after Criegee intermediate.
In contrast to the above systems, no product bands were seen in the twin jet codeposition
of the reactants. Further, annealing these matrices to 35 K did not lead to the formation of any
product bands. This is consistent with the small rate constant for the reaction of ozone with
propene (6.80×106 cm3 mol-1 s-1), and less substituted alkenes in general.9 In the future, it will be
26
useful to choose a chemical system with a higher rate constant at room temperature to observe
the early intermediates capable using this deposition mode.
The photochemical reaction of ozone with propene did, however, lead to the series of
product bands listed in Table 3.3 This result is characteristic of the photo detachment of an O
atom from ozone when irradiated and subsequent O atom reaction with propene.10,11 Several of
the most intense absorptions were detected and assigned to literature spectra and calculated data
for propanal, epoxypropane, and acetone.4,12,13 The postulate has been suggested that for the
reaction of O atoms with alkenes seen in Figure 3.5, attack occurs at the least substituted carbon
atom in the double bond, leading to either stabilization there and formation of the appropriate
aldehyde (propanal here) or the formation of a three membered epoxide ring.14 However, the
matrix may make other pathways available, through steric constraints or rearrangement. For
example, the reopening of the epoxide ring can leave the O atom on either side of the carbon
atoms involved in the double bond, hence the propanal and acetone observed.15 Although matrix
isolation has been used to study the O atom attack on alkenes using N2O as an oxygen source,
this is the first matrix study where ozone is used as an oxygen source with propene.
Conclusions
The merged jet deposition of ozone and propene into argon matrices led to the
observation of stable reaction products. In contrast, with twin jet deposition, a reaction did not
occur, indicating that an alkene with a higher rate constant for a reaction with ozone is required
under these conditions. Although the intermediates proposed by Criegee were not detected, the
formation of formaldehyde and acetaldehyde gave support that the mechanism is consistent for
this system. The photochemical reaction of ozone with propene led to O atom attack on a carbon
at the double bond and the formation of epoxypropane, propanal, and acetone. These conclusions
27
were supported by
18
O isotopic labeling, by comparison to authentic infrared spectra where
available, and by B3LYP/6-311G++(d,2p) density functional calculations.
28
References:
(1)
Andrews, L.; Spiker, R. C. J. Phys. Chem. 1972, 76, 3208.
(2)
Barnes, A. J.; Howells, J. D. J. Phys. Chem. 1973, 69, 532.
(3)
Vedova, C. D.; Sala, O. J. Raman Spectrosc. 1991, 22, 505.
(4)
Polavarapu, P. L.; Hess, B. H.; Schaad, L. J. J. Chem. Phys. 1985, 1705.
(5)
Herron, J. T.; Huie, R. E. J. Chem. Kinet. 1978, 10, 1019.
(6)
Sander, W.; Gantenberg, M. Spectrochim. Acta, Part A 2005, 62, 902.
(7)
Diem, M.; Lee, K. C. J. Phys. Chem. 1982, 86, 4507.
(8)
Reva, I. D. Spectrochim. Acta, Part A 1994, 50, 1107.
(9)
Atkinson, R.; Carter, W. P. Chem Rev. 1984, 84, 437.
(10)
Parker, J. K.; Davis, S. R. J. Am. Chem. Soc. 1999, 121, 4271.
(11)
Parker, J. K.; Davis, S. R. J. Phys. Chem. A 2000, 104, 4108.
(12)
Gupta, V. P. Chem. Phys. 1984, 90, 291.
(13)
Nowak, M. J.; Szczepaniak, K.; Baran, J. W. J. Mol. Struct. 1987, 47, 316.
(14)
Cvetanovic, R. J. Can. J. Chem. 1958, 36, 291.
(15)
Ault, B. S. J. Mol. Struct. 1990, 222, 1.
29
Chapter 4
Investigation of the Thermal and Photochemical Reactions of Ozone with
2,3-dimethyl-2-butene (DMB)
Introduction
Energy dissipation of the intermediates in the Criegee mechanism may come either
through bimolecular collisions (such as with excess Ar) or by internal vibrational, rotational,
translational (VRT) energy transfer. The substituents on the alkene provide a means to
control the number of internal degrees of freedom for the alkene involved in the reaction with
ozone and thus the VRT energy transfer rate. DMB is a tetrasubstituted alkene with a
relatively high rate constant for a reaction with ozone (6.99×108 cm3 mol-1 s-1) at 298 K when
compared to less substituted alkenes in general.1 On the other hand, tetra-substituted alkenes in
ozonolysis reactions are thought to form a Criegee intermediate with two methyl group
substituents, making the recombination reaction to form the secondary ozonide more difficult. 2
As described below, the current study has led to the observation of the primary (POZ) and
secondary (SOZ) ozonides as well as the Criegee intermediate (CI) for the DMB/O3 system.
Results
Prior to any deposition experiments, blank experiments were run on each of the parent
reagents used in this study. Hydroxyacetone and acetone blank spectra were also obtained for
comparison with experimental spectra (Figures S4.1 and S4.2). In each case, the blanks were in
good agreement with literature spectra.3-6
Twin Jet 16O3 + DMB: A series of twin jet experiments were conducted with samples of Ar:O3
= 250 and Ar:DMB = 250. In a typical experiment, a number of new bands were observed after
19.0 h of deposition. The matrix was then annealed to 35 K and recooled to 19 K. A spectrum
was then recorded, and the new absorptions grew by approximately 200%; these are listed in
30
Table 4.1 and a portion of the spectra can be seen in Figure 4.1. The experiment was repeated
several times, using different sample concentrations varying from M/R (matrix/reactant) = 167 to
M/R = 500. The results were reproducible, with product band intensities that varied proportional
with sample concentrations. Then, the annealed matrix was irradiated for 1.0 h with the filtered
(λ ≥ 220 nm) output of a medium-pressure Hg arc lamp. This produced many new product bands,
shown in Figure 4.2; Table 4.2 shows the full list of product absorptions produced as a result of
irradiation. Several product bands that were present before irradiation decreased after irradiation.
In one experiment, the wavelength of irradiation was varied from λ ≥ 580 nm to λ ≥ 220 nm.
Product bands present before irradiation decreased and new bands that grew in became more
intense when irradiating from longer to shorter wavelengths. In the cases where O2 was used as a
matrix material, the absorptions that resulted from irradiation were much more intense than when
Ar was used (Figure S4.3).
Merged Jet 16O3 + DMB: Initial merged jet experiments were conducted with samples of Ar:O3
= 250 and Ar:DMB = 250, using a 2.0 m merged or reaction region held at room temperature.
This configuration allows for increased gas phase reaction time for the reactions relative to twin
jet deposition and prior to matrix deposition. In each of the merged jet experiments, the parent
bands of both reagents were substantially reduced in intensity, indicating that a reaction was
occurring. In addition, many new product bands were observed throughout the spectrum,
including several intense bands in the carbonyl stretching region. Figure S4.4 shows a portion of
the spectrum from one merged jet experiment. Some of the new bands were similar to those in
the twin jet experiments but the bands were generally more similar to the twin jet irradiation
experiments. These bands were reproduced in several experiments, all with the merged region
31
Table 4.1 Band Positions and Assignments for the Initial Intermediates in the Thermal
Reaction of O3 with DMB
exptl.
bandsa
650
ν16O - ν18O
calcd. calcd. exptl.
bandsb shift shift
647
-7
-8
assignment
POZ
691
689
-27
-27
POZ
729
760
-40
-39
POZ
829
827
-31
-32
SOZ
842
841
-24
-22
POZ
854
865
-25
-11
POZ
870
848
-20
-33
SOZ
880
854
-44
-34
CI
949
952
-4
0
POZ
1092
1017
0/-7
0/-7 POZ/acetone
1141
POZ*
1146
1160
-2
-3
POZ
1154
1177
-2
-2
POZ
1195
1184
-1
0
POZ
1206
1223
-4
-4
SOZ
1245
1224
-1
0
POZ
1349
1388
0
0
acetone
1354
1465
0
0
acetone
1362
1469
0
0
acetone
1370
1475
-2
0
acetone
1393
1403
-1
0
POZ
1422
acetone*
1489
1491
0
-3
POZ
1713
acetone*
1718
1785
-35
-33
acetone
a
-1
b
Frequencies in cm . Calculated at the
B3LYP/6-311G++(d,2p) level of theory.
*Assignments based on literature for POZ and
blank spectra for acetone.6 Theoretical error
±3%. Experimental error ≤ ±1 cm-1.
32
0.80
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.00
960
880
920
840
800
Wavenumbers (cm-1)
760
720
680
Figure 4.1 Select region of IR spectra from twin jet deposited Ar:16O3:DMB = 500:1:1. Black
trace is after 19 hrs of depositing. Blue trace is after annealing to 35K.
1848
1750
1650
1550
1450
1350
1250
1150
1050 983
Figure 4.2 IR spectra of twin jet deposited O2:O3:DMB = 500:1:1. Blue trace is after depositing
for 19 h. Black trace is the result after irradiating with  ≥ 220nm for 1 h.
33
Table 4.2 Band Positions and Assignments for New Product Absorptions from the Twin Jet
Deposition of Ozone with DMB upon Irradiation with Light of λ ≥ 220 nm
exptl.a
literature (Ar matrix)b
assignment
656
655
HA
847/848
TMO/MA
846
899*
DMDO
900
1094*
DMDO
1022
1095/1092
HA/AC
1093
1142
TMO
1142
1205
TMO
1206
1217
AC
1224
1245
FOR
1244
1228
HA
1256
1286
HA
1283
1302
CH4
1301
1209*
DMDO
1330
1354/1354
PC/AC
1354
1362
AC
1363
1369/1361/1370
PC/HA/MA
1373
1381
1380
TMO
1406/1407
1404
TMO/AC
1422
1422/1407
PC/AC
1440
1438/1439/1444
TMO/PC/AC
1450
1452
AC
1460
1462
MA
1489
1471
TMO
1712
1713
PC
1718
1722/1717
AC/PC
1733
1731
HA
1756
1761
MA
2136
2138/2138
CO/FOR
3431br
3505
HA
a
-1 b
Frequencies in cm . References 3, 4, 8, 12, 14, 17, 18.
*Liquid phase IR spectra. HA=hydroxyacetone,
TMO=tetramethyloxirane, PC=3,3-dimethyl-2-butanone,
AC=acetone, MA=methyl acetate, CO=carbon monoxide,
FOR=formaldehyde, and DMDO=dimethyldioxirane.
Experimental error ≤ ±1 cm-1.
34
at room temperature. Additional merged jet experiments were conducted, varying both reactants
from M/R (matrix/reactant) = 167 to M/R = 500. These experiments provided a variation in
product concentration without compromising dilution ratios and subsequent secondary reactions.
Product absorption intensities were directly proportional to this variation of reactant
concentrations.
Concentric Jet 16O3 + DMB: The reaction of ozone with 2,3-dimethyl-2-butene was explored in
several concentric jet experiments as well, all with concentrations of 250:1 for each reagent, and
d ranging from -11.0 to +1.0 cm. Table S4.1 lists the intensities of three most intense bands for
intermediates from the twin jet experiment. The intensities of the bands at 729 for the POZ, 1206
for the SOZ, and 1721 cm-1 for acetone were monitored as a function of d in the concentric jet
experiments. In an experiment with d = +1 cm, many of the bands from the twin jet annealed
experiment were seen, although with much less intensity. When an experiment was conducted
with d = 0 cm, similar results were seen with even lower intensities. Going from d = 0 cm to d =
-1 cm, the three bands monitored increased slightly at similar rates. From d = -1 cm to d = -6
cm, both bands at 729 and 1721 cm-1 decreased while the 1206 cm-1 band increased. Figure S4.5
shows representative regions at d = -1 cm and d = -6 cm. From d = -6 cm to -11 cm, a decrease
in the three bands was observed. No new bands (i.e., bands not seen in either twin or merged jet
experiments) were seen in these experiments.
18
O3 + DMB: Twin, merged, and concentric jet experiments were also conducted with samples
of Ar:18O3 = 250 deposited with samples of Ar:DMB = 250. Results paralleled those obtained for
the normal isotopic species, with many product bands showing an isotopic shift relative to the
corresponding
16
O3 experiments. Many product bands were observed, some of which were
slightly less intense than the pure 16O corresponding bands, while the parent bands were reduced.
35
Multiple twin jet experiments were conducted with samples of Ar:DMB = 250
codeposited with Ar:16,18O3 = 250. The resulting product bands were less intense than in the pure
16
O3 and
18
O3 experiments, while several new, less intense red shifted bands were present. The
positions and assignments for these bands are given in Table 4.3.
Results of Calculations
To complement the experimental data, DFT calculations were carried out on all
intermediates and possible products. Energy minima were located for the optimized structures
and the vibrational spectra were calculated for both normal isotope species in oxygen containing
molecules and
18
O-substituted isotopomers. Calculated structures for the anticipated
intermediates of interest and additional possible products are presented in Figures 4.3 and S4.6.
Key structural parameters for the Criegee intermediate in comparison with the similar
acetone molecule can be seen in Table S4.2. Of particular importance are the calculated
vibrational frequencies and intensities for the POZ, Criegee intermediate, and SOZ; these are
listed in Table 4.1. In addition to the fundamental absorptions for each species, the 18O shifts of
the most intense absorptions for each species are very valuable when comparing to experimental
data. For the POZ, the most intense absorption is calculated at 760 cm-1 with a -40 cm-1 18O shift.
This is ascribed to the O-O-O antisymmetric stretching mode. The characteristic O-O stretch of
the Criegee intermediate was calculated at 910 cm-1 with a -44 cm-1 shift with
18
O. The most
intense absorption of the SOZ was calculated at 1223 cm-1 with a smaller 18O shift of -4 cm-1 and
is associated with a C-O-C stretching motion. These theoretical calculations were compared to
the experimental observations from twin, merged and concentric jet deposition experiments.
Discussion
An important goal in the current study of the ozone/DMB system is to provide
36
a)
b)
c)
Figure 4.3 Calculated structures for the (a) primary ozonide, (b) Criegee intermediate, and (c)
secondary ozonide from the reaction of ozone with DMB.
Table 4.3 Product Band Positions and Assignments for the Intermediates in the Ozonolysis of DMB
experimental positiona and shifts
calculatedb position and shifts
16
16
O
16,18O
18O
O
16,18O
18O
729 -11 -15 -22 -26 -39
760 -12 -17 -23 -28
-40
854
-3
-5
-11
865
-1
-5 -16 -24
-25
870
-33
848
-4
-4
-6
-6 -17 -17 -20
880 -12 -20
-34
910 -18 -25
-44
1206
-4
1223 -1
-1
-2
-3
-3
-3
-4
1718
-33
1785
-35
a
-1 b
Band positions in cm . Calculated using the B3LYP 6-311G ++ (d,2p) level of theory.
Theoretical error ±3%. Experimental error ≤ ±1 cm-1.
37
assignment
POZ
POZ
SOZ
CI
SOZ
acetone
experimental evidence for the reaction mechanism by the direct observation of the early
intermediates. In particular, Criegee predicted the formation of a POZ, (which has been observed
previously),6 as well as the Criegee intermediate and the SOZ. These latter two species have not
been observed experimentally in studies of the gas phase ozonolysis of DMB.2 The POZ may
decompose rapidly forming acetone, a species whose infrared spectrum in an argon matrix has
been reported,4 and the Criegee intermediate. Since the starting alkene is symmetrical, the
acetone/CI pair may recombine to form a single secondary ozonide, or may separate and undergo
stabilizing collisions.
O3 + DMB Twin Jet. Twin jet, merged jet and concentric jet deposition were used to probe
different time and temperature regimes with respect to the mixing and reacting of O3 with DMB.
Twin jet deposition allows for only a brief amount of mixing on the surface of the condensing
matrix surface. Upon initial twin jet deposition, a number of moderately weak absorptions were
observed as listed in Table 4.1. Annealing these matrices to 35 K resulted in the substantial
growth (200% increase) of these absorptions. These observations indicate that reaction is
occurring at 35 K and that the barrier to this reaction must be very low (3/2RT ≈ 0.1 kcal mol-1 at
35 K). Also, the growth of approximately 30 absorptions suggests that more than one species is
being formed. In addition, the bands in these twin jet experiments were different than those in the
observed in the merged jet experiment, where most of the products are the anticipated stable
oxidation products. Likewise, the product bands observed in twin jet experiment were entirely
different than those in the irradiation experiments, where photochemical products are observed.
These results are in agreement with recent studies from this laboratory on related systems.7
As outlined below, substantial evidence supports the assignment of product absorptions
in Table 4.1 to the primary (POZ) and secondary (SOZ) ozonides of DMB, as well as to the
38
Criegee intermediate–acetone pair. First, direct comparison between several of these
experimental absorptions to the POZ absorptions reported in the literature supports formation of
the POZ. For example, the most intense literature bands for the primary ozonide are at 729 and
1146 cm-1.6 Relatively intense bands were observed in the current study at those same positions
as seen in Table 4.1. In addition, while the previous study did not incorporate
18
O labeling or
theoretical calculations, these were an integral part of the present study. Theoretical calculations
for the
18
O-labeled POZ predict a -40 cm-1 isotopic shift for the intense absorption at 760 cm-1
(calculated, unscaled). The experimental band at 729 cm-1 was in excellent agreement with this
prediction, with a -39 cm-1
18
O shift. Further, six bands are anticipated in the scrambled
16,18
O3
experiments and all six were observed. These can be seen in Table 4.3. Finally, there was good
agreement between experimental observations and theoretical calculations for all observed
vibrational bands of the POZ and their corresponding
18
O shifts. Thus, the POZ of DMB is
clearly formed and detected in these experiments.
A second key conclusion comes from the comparison between these twin jet spectra and
a blank infrared spectrum of acetone in argon (Figure S4.1). This comparison strongly supports
the formation of acetone upon initial deposition and its growth upon annealing to 35 K. All of the
most intense bands of acetone were observed in the twin jet experiments and showed the
anticipated
18
O shifts. Of note, the C=O stretch at 1718 cm-1 was the most intense product
absorption in the twin jet experiment and was slightly shifted (4-5 cm-1) compared to the blank
acetone experiment. This is thought to be from an interaction between the acetone molecule and
Criegee intermediate in the argon cage. The 18O shift of this band, -33 cm-1, was the anticipated
shift. In addition, both acetone isotopomers at 1718 and 1685 cm-1 were observed in the
16,18
scrambled experiments, demonstrating the presence of a single O atom in this product species.
39
O3
One additional product band in the twin jet experiments was a weak band that was
consistently observed at 880 cm-1. This band shifted -34 cm-1 to 846 cm-1 with
addition, when 50% scrambled
16,18
18
O labeling. In
O3 was employed, a quartet of nearly equally intense bands
was observed at 880, 868, 860, and 846 cm-1 as can be seen in Figure S4.7. The most apparent
origin of an isotopic quartet is from a species with two in equivalent oxygen atoms. The Criegee
intermediate, a carbonyl oxide is one of a relatively few species that meets this requirement.
Moreover, the antisymmetric C=O-O stretching mode (often described as an O-O stretch) has
been observed for carbonyl oxides in the vicinity of 900 cm-1, and was observed at 922 cm-1 for
the Criegee intermediate of cis-2-butene.7
Theoretical calculations predict that the most intense band of the Criegee intermediate
will come at 910 cm-1 (unscaled) with a 44 cm-1 18O shift. This matches well the observed band
and shift, taking into account that such calculations are typically 3% to high. Moreover, the
positions of the two intermediate isotopic bands at 860 and 868 cm-1 are well reproduced by
calculations. It is noteworthy that calculations predict only a single intense band for the CI, along
with a number of quite weak bands. Thus, the observation of a single product band is in keeping
with the prediction of the calculations.
Other possible products that might form from the rearrangement and stabilization of the
Criegee intermediate include hydroxyacetone via internal O atom transfer or methyl acetate
through a dioxirane intermediate.2 However, these are species for which infrared spectra are
available3,8 (a blank was run on hydroxyacetone in solid argon to provide an authentic sample).
The key infrared absorptions of these species were entirely absent. Moreover, they have no
absorptions that could account for the product band at 880 cm-1. Finally, these unimolecular
stabilization pathways have activation energies calculated to range from approximately 10 to 20
40
kcal mol-1.9 Thus, these pathways are much less likely and do not appear to play a role under the
present experimental conditions.
Finally, the Criegee mechanism predicts the formation of the Criegee intermediate along
with acetone from the decomposition of the POZ of DMB. In view of the definitive observation
of acetone (see above), the very good agreement of calculation and experiments for the C=O-O
stretch mode and overall, the observation of an isotopic quartet in the scrambled
16,18
O3
experiments and the lack of observation of anticipated rearrangement products of the Criegee
intermediate, the evidence collectively supports assignment of the 880 cm-1 band to the Criegee
intermediate of 2,3-dimethyl-2-butene. Further, this provides definitive evidence that tetrasubstituted alkenes follow the Criegee mechanism.
Earlier studies have suggested that formation of a secondary ozonide from the Criegee
intermediate of a tetra alkyl-substituted alkenes would be more difficult than from a lesser
substituted alkene.2 Later studies have disputed this suggestion. While the secondary ozonide of
DMB has not been reported in the gas phase or in inert matrices, one study reported the
observation of this species immobilized in a polyethylene film.10 However, this study lacked
isotopic labeling and theoretical calculations, and the broad spectral features made this
identification tentative. In the present study, additional weak product absorptions were observed
at 1206, 870, and 829 cm-1. Incorporation of
18
O labeling and comparison to theoretical
calculations for the SOZ provides good evidence that these bands can be assigned to the SOZ of
DMB. In particular, the most intense calculated absorption for the SOZ came at 1223 cm-1 with a
-4 cm-1 calculated
18
O shift without scaling. This corresponds nicely to the most intense
experimental absorption for the SOZ at 1206 cm-1 that had an
18
O shift of -4 cm-1. Similar
agreement of experiment and theory was seen for the 829 and 870 cm-1 bands, as shown in Table
41
4.1. While many more bands are anticipated for the SOZ, additional absorptions were not
observed in part due to overlap with parent bands in the reaction spectrum and in part due to low
intensities. No additional bands were observed for the SOZ in the
16,18
O3 mixed isotope
experiment. Considering that there are eight calculated isotopomers for each SOZ band, the
intensities of each individual band in the experimental study would be greatly reduced to the
point that they were not observed. Table 4.3 shows calculated positions for the SOZ isotopomers.
O3 + DMB Twin Jet Photochemistry: In twin jet argon matrix experiments that were irradiated
with light of λ ≥ 220 nm, the absorptions listed above for the early intermediates decreased and
several new weak product bands were observed. When the same experiment was conducted with
O2 as the matrix material, the same new photochemical product absorptions were observed, and
with increased intensity (Figure S4.3). These results indicated that two different processes are
occurring. First is the decomposition of the early intermediates and second is the photodetachment of an O atom from ozone upon irradiation followed by O atom reaction with an
available substrate molecule. The reaction of O atoms with alkenes has been proposed to occur
as shown in Figure 4.4, with O atom attack occurring at the less substituted carbon atom in the
double bond.11 This can lead to either stabilization and formation of the appropriate ketone (3,3dimethyl-2-butanone in the system under study here) or the formation of a three membered
epoxide ring.
Using O2 as the matrix material is thought to increase the mobility of the O atoms and as
a result, increase the likelihood that the O atom will find a substrate molecule and react. Most of
the observed product absorptions that grew in when irradiated from λ ≥ 220nm to λ ≥ 580 nm
can be assigned to either acetone, tetramethyloxirane, or 3,3-dimethyl-2-butanone based on
literature spectra and theoretical calculations.4,12
42
Figure 4.4 Scheme for the O atom attack on the double bond of DMB.
43
It is noteworthy that the 880 cm-1 band assigned to the Criegee intermediate was reduced
in intensity when irradiation with light with  < 550 nm. At the same time, several new
absorptions were observed when irradiating in this wavelength range. These included two weak
carbonyl stretch absorptions at 1733 and 1756 cm-1 and a broad O-H stretch at 3431 cm-1. These
observations suggest destruction of the CI and formation of related products. As discussed
above, unimolecular rearrangement products, including hydroxyacetone, dioxirane and methyl
acetate, are likely candidates. In this case, the energy required for the Criegee intermediate to
overcome the calculated 10-20 kcal mol-1 barrier leading to these stable compounds is available
through absorption of light. Sander found that while generating carbonyl oxides (Criegee
intermediates) via another route, irradiation at select wavelengths led to different products (λ =
515 nm leads to dioxirane formation and further to an ester at λ = 438 nm).13,14 In similar
manner, the bands observed here at 1733, 1756 and 3431 cm-1 are assigned to hydroxyacetone
and methyl acetate. In addition there are three weak bands at 900, 1022, and 1330 cm-1 assigned
to the dioxirane14 that serves as an intermediate between the Criegee intermediate and methyl
acetate. In Figure 4.5, the Criegee intermediate band at 880 cm-1 decreases as the dioxirane band
at 900 cm-1 increases. These results present direct evidence of the wavelength dependence of the
photodestruction of a Criegee intermediate.
O3 + DMB Merged Jet: In merged jet deposition, the mixing of ozone and DMB occurred at
room temperature in a flow tube outside of the matrix cell. Additional reaction time is available
in this mode compared to twin jet and has led to “late” thermal reaction products in previous
studies. In these experiments, bands of the precursors and early intermediate species decreased
significantly compared to twin jet spectra and a number of new product absorptions were
44
Dioxirane
936
930 925
920
915
910 905
900
895
Criegee
Intermediate
890
885 880
875
870
865
Figure 4.5 IR spectra of twin deposited Ar:16O3:DMB = 500:1:1. Black trace is spectrum upon
annealing to 35 K. Blue trace is upon irradiating with λ ≥ 220 nm.
45
observed. This indicates that extensive reaction occurred during the transit through the merged
jet or reaction region. In particular, there were numerous product bands in the carbonyl stretching
region as well as a broad absorption at 3497 cm-1 suggesting the presence of an O-H containing
species. Product identification can be made from the known infrared spectra in Ar matrices for
methyl
glyoxal,
hydroxyacetone,
acetone,
tetramethyloxirane,
and
3,3-dimethyl-2-
butanone.3,4,15,16 While mostly stable products were formed, these are consistent with the Criegee
mechanism and secondary reactions of the Criegee intermediate. The observation of
tetramethyloxirane and 3,3-dimethyl-2-butanone in this system may be the result of the loss of an
O atom from the Criegee intermediate and subsequent reaction with the alkene. Other final
products are in agreement with a related gas phase study of the reaction of DMB with ozone at
room temperature in a static system with rapid mixing that yielded methyl glyoxal, methyl
acetate, and hydroxyacetone as major products. Niki et al. noted that the presence of these
carbonyl compounds in normal gas phase conditions are a result of further reactions of the
Criegee intermediate and not decomposition of the secondary ozonide.16 Unimolecular
stabilization pathways can be seen in Figure S4.8. Not only do these results give additional
evidence for the Criegee mechanism, but more importantly, the formation and rearrangement of
the Criegee intermediate.
O3 + DMB Concentric Jet: In concentric jet experiments, the relative amounts of the
intermediates can be monitored by the intensity of infrared absorptions assigned to each species
as a function of system geometry. All of the absorptions for the POZ, SOZ, and acetone seen in
twin jet experiments were observed using concentric jet; the more intense absorptions for each
species were monitored. While the 880 cm-1 band of the Criegee intermediate was too weak to
monitor in these concentric jet experiments, the behavior of the acetone band will serve to probe
46
the behavior of the CI/acetone pair. As discussed above, bands at 729, 1721, and 1206 cm-1 have
been assigned to the POZ, acetone, and SOZ respectively and were used to monitor the relative
amounts of these three intermediates. In concentric jet experiments with d ≥ 0, the results were
very similar to twin jet with the observation of these three bands but with slightly less intensity.
As d became negative from -1 to -6 cm the bands associated with the POZ and acetone decreased
and the SOZ yield increased. From d = -6 to -11 cm, the three bands decreased as the merged jet
products (carbonyl compounds) increased dramatically, suggesting that this geometry
approached that of merged jet deposition. No entirely new bands were observed using any value
of d, therefore concentric jet was able to successfully transition between twin and merged jet
regimes. Following the Criegee mechanism, as the SOZ is formed, there should be a decrease in
the POZ, Criegee intermediate (although not seen here), and acetone. The observations here are
consistent with this mechanism.
Conclusions
The codeposition of O3 with DMB into Ar matrices under varying conditions has led to
the observation of the early reaction intermediates and stable reaction products. Twin jet
deposition followed by warming to 35 K led to moderately intense product bands assigned to the
POZ, SOZ, the Criegee intermediate, and acetone. The DMB POZ has been observed and
characterized previously; the present study enhanced the earlier work with the addition of
18
O
isotopic labeling and theoretical calculations. The formation and isolation of the Criegee
intermediate resulting from a tetrasubstituted alkene increases the overall understanding of the
mechanism of the ozonolysis of alkenes. The identification and spectroscopic characterization of
the SOZ of DMB in argon matrices was successful as well. Irradiation of these matrices resulted
in products formed from the unimolecular rearrangement of the Criegee intermediate,
47
photodestruction of the POZ and SOZ, and O atom attack on DMB. The formation of both
hydroxyacetone and methyl acetate in the photochemical studies suggest a rearrangement of the
Criegee intermediate. In contrast, merged jet deposition led a variety of carbonyl-containing final
products, depending on the length of the flow reactor.
Supporting Information
Supplemental spectra, figures and data tables are available in Appendix A.
48
References
(1)
Atkinson, R.; Carter, W. Chem. Rev. 1984, 84, 437-470.
(2)
Bailey, P. Ozonation in Organic Chemistry Olefinic Compounds; Academic Press, Inc.:
New York, 1978.
(3)
Sharma. A.; Reva, I.; Fausto, R. J. Phys. Chem. A 2008, 112, 5935–5946.
(4)
Cosani, K. J. Phys. Chem. 1987, 91, 5586-5588.
(5)
Andrews, L.; Spiker, R. C. J. Phys. Chem. 1972, 76, 3208.
(6)
Samuni, U.; Haas, Y.; Fajgar, R.; Pola, J. J. Mol. Struct. 1998, 449, 177-201.
(7)
Clay, M.; Ault, B. S. J. Phys. Chem. A 2010, 114, 2799-2805.
(8)
Patten, K.; Andrews, L. J. Phys. Chem. 1986, 90, 1073-1076.
(9)
Epstein, S.; Donahue, N. J. Phys. Chem. A 2008, 112, 13535–13541.
(10)
Griesbaum, K.; Volpp, W.; Greinert, R.; Greunig, H.; Schmid, J.; Henke, H. J. Org.
Chem. 1989, 54, 383-389.
(11)
Cvetanovic, R. Can. J. Chem. 1958, 36, 623.
(12)
Nakata, M. Spectrochim. Acta, Part A 1994, 50A, 1455-1465.
(13)
Wierlacher, S.; Sander, W.; Marquardt, C.; Kraka, E.; Cremer, D. Chem. Phys. Lett.
1994, 222, 319.
(14)
Murray, R. Chem. Rev.1989, 89. 1187-1201.
(15)
Mucha, M.; Saldyka, M.; Mielke, Z. Pol. J. Chem. 2009, 83, 943-956.
(16)
Niki, H.; Savage, C.; Breitenbach, L.; Hurley, M. J. Phys. Chem 1987, 91, 941-946.
(17)
Diem, M.; Lee, E. J. Phys. Chem. 1982, 86, 4507-4512.
(18)
Frayer, F.; Ewing, G. J. Chem. Phys. 1968, 48, 781.
49
Chapter 5
Investigation of the Thermal and Photochemical Reactions of Ozone with Styrene in Argon
and Krypton Matrices
Introduction
Styrene is described as a phenyl-substituted ethene rather than an aromatic alkene which
usually have a much lower rate constant via a reaction with ozone at 298 K. In fact, the
conjugated ring increases (2X) the reactivity of styrene (1.30 x 107 cm3 mol s-1) for this reaction
when compared to the methyl substituted propene.1 Ozone is thought to attack the vinyl double
bond of styrene leaving the phenyl ring intact. The ozonolysis of styrene results in the formation
of an asymmetric primary ozonide. The primary ozonide can decompose in two separate
directions forming two different Criegee intermediates, the benzaldehyde-O-oxide and
formaldehyde-O-oxide, with their aldehyde counterparts. These pairs can combine to form three
cross secondary ozonides. Most recently, some have used matrix isolation infrared spectroscopy
to isolate carbonyl oxides (or Criegee intermediates) by irradiating a synthetic diazo compound
that yields a triplet state carbene and subsequent reaction with O2 to form the benzaldehyde-Ooxide.2 Styrene was chosen in this study due to the well-known characterization of one of its
intermediates, the benzaldehyde-O-oxide Criegee intermediate via this latter route. As a result,
the present study has led to the observation of early intermediates and stable products for the
ozonolysis reaction with styrene.
Results
Prior to any deposition experiments, blank experiments were run on each of the parent
reagents used in this study.3,4 A benzaldehyde blank spectrum was also obtained for comparison
with experimental spectra (Figure S5.1). In each case, the blanks were in good agreement with
literature spectra.5
50
Twin Jet
16
O3 + Styrene: A series of twin jet experiments were conducted with samples of
Ar:16O3 = 250 and Ar:styrene = 250. In these experiments, no changes in the spectra were
observed after 19.0 h of codeposition with temperature held at 19 K. This matrix was then
annealed to 35 K and recooled to 19 K. A spectrum was then recorded and two weak bands grew
in at 763 and 1460 cm-1. The experiment was repeated several times, decreasing the M/R
(matrix/reactant) ratio to M/R = 167. The results were reproducible, with the same two weak
bands observed. These matrices were subsequently irradiated for 1.0 h with a quartz filtered (λ ≥
220 nm) output of a medium-pressure Hg arc lamp leading to the formation of a number of new
bands. Figure 5.1 shows a portion of the spectrum where new the bands that grew in and their
assignments are listed in Table 5.1. In another experiment, the diluted reactants (M/R = 250),
were codeposited into an already “warm” matrix held at 35 K for 24 hrs. A number of bands
were observed and are listed in Table S5.1. Irradiation of the “warm” deposited experiment
resulted in loss of the matrix as a result of melting.
Next, krypton was used as the matrix material to permit annealing to higher temperatures.
In the twin jet krypton experiments with Kr:16O3 = 200 and Kr:styrene = 200 no new bands were
observed after initial codeposition at 19 K over 24 hrs. The krypton matrix was annealed to 68 K
as seen in Figure 5.2. Several medium-to-weak bands grew in and are listed in Table 5.2. Then,
the annealed matrix was irradiated for 1.0 h with a quartz filtered (λ ≥ 220 nm) output of a
medium-pressure Hg arc lamp. This resulted in loss of the matrix due to melting.
Merged Jet
16
O3 + Styrene: Initial merged jet experiments were conducted with samples of
Ar:16O3 = 250 and Ar:styrene = 250, using a 2.0 m merged or reaction region at room
temperature. This configuration allows for increased gas phase reaction time for the reactions
relative to twin jet deposition and prior to matrix deposition.
51
Figure 5.1 C=O stretch region of the infrared spectrum of a matrix formed by the twin jet
deposition of a sample of Ar:16O3 = 250 with a sample of Ar:Styrene = 250 annealed to 35K and
irradiated with λ ≥ 220 nm for 1 h. Blue trace is before irradiation and red trace is after
irradiation. New product bands are labeled in blue.
Table 5.1 Band Assignments from Twin Jet Ar:O3:Styrene Irradiated Experiment
16
O (cm-1) 18O (cm-1) exptl. shift calcd. shift
assignment
literaturea
753
753
0
0
phenyloxirane
760
760
0
-1
phenyloxirane
885
865
-20
-18
phenyloxirane
987
984
-3
-3
phenyloxirane
1055
1049
-6
0
phenyloxirane
1071
1071
0
-1
phenylacetaldehyde
1128
1124
-4
-3
phenyloxirane
1268
1268
0
-1
acetophenone
1268
1314
1314
0
-1
acetophenone
1312
1358
1358
0
0
acetophenone
1355
1392
1384
-8
-6
phenylacetaldehyde
1397
1393
-4
-1
phenyloxirane
1480
1479
-1
-1
acetophenone
1482
1698
-33
acetophenone
1699
1737
1701
-36
-37
phenylacetaldehyde
1743
sh
phenylacetaldehyde
a
Ref. 11 in xenon matrix at 20 K. Calculated at B3LYP/6-311G++(d,2p). Theoretical error
±3%. Experimental error ≤ ±1 cm-1.
52
Figure 5.2 The lower red trace is the infrared spectra of a matrix formed by the twin jet
deposition of a sample of Kr:16O3 = 250 with a sample of Kr:Styrene = 250 upon annealing to 68
K. The labeled bands are those that grew upon annealing. The upper trace is the same
experiment, however with 18O labeling.
53
Table 5.2 Band Assignments from Twin Jet Kr:O3:Styrene Annealed to 68 K
exptl. 16O (cm-1)
exptl. 18O (cm-1)
exptl. shift (cm-1)
calcd. shift (cm-1)
assignment
684
655
-29
-31
primary ozonide
740
724
-16
-24
primary ozonide
761
759
-2
-1
primary ozonide
934
921
-13
-16
Criegee
intermediate
972
957
-15
-16
primary ozonide
1058
1049
-9
-21
1212
1287
1212
1287
0
0
-
secondary
ozonide
benzaldehyde
benzaldehyde
1311
1311
0
-
benzaldehyde
1367
1367
0
-1
1458
1458
0
-
secondary
ozonide
benzaldehyde
1694
1645
-49
-
benzaldehyde
1724
1672
-52
-
benzaldehyde
1734
1688
-46
-
formaldehyde
Calculated at B3LYP/6-311G++(d,2p). Theoretical error ±3%. Experimental error ≤ ±1 cm-1.
54
New product bands were observed throughout the spectra, including several medium bands in the
carbonyl stretching region. Figure S5.2 shows a portion of the spectrum from one merged jet
experiment. Some of the new bands were similar to those in the twin jet krypton experiments.
These bands were reproduced in several experiments, all with the merged region held at room
temperature. Additional merged jet experiments were conducted, varying both reactants from
M/R (matrix/reactant) = 167 to M/R = 500. Product absorption intensities were proportional to
this variation of reactant concentrations. Irradiation (λ ≥ 220 nm) of merged jet experiments
resulted in bands that increased intensity after 1 h. New bands also grew in as a result of
irradiation and are assigned in Table 5.3.
18
O3 + Styrene: Twin, and merged jet
18
O3 labeled experiments were also conducted with M/R
ratios = 250 in both argon and krypton experiments. Results paralleled those obtained for the
normal isotopic species, with many product bands showing an isotopic red shift relative to the
corresponding
16
O3 experiments. Many product bands were observed, some of which were
slightly less intense than the pure 16O corresponding bands.
Results of Calculations
To complement the experimental data, DFT calculations were carried out on
intermediates and expected products. Energy minima were located for the optimized structures
and the vibrational spectra were calculated for both normal isotope species in oxygen containing
molecules and
18
O-substituted isotopologues. Calculated structures for the anticipated
intermediates of interest and additional possible products are presented in Figures 5.3 and S5.3.
Of importance are the calculated vibrational frequencies and intensities for the primary ozonide,
Criegee intermediates, and secondary ozonide; they are listed in Table S5.2. In addition to the
fundamental absorptions for each species, the calculated 18O shifts of the most intense
55
a)
c)
b)
d)
Figure 5.3 Calculated structures for the (a) primary ozonide, (b) benzaldehyde-O-oxide Criegee
intermediate, (c) formaldehyde-O-oxide Criegee intermediate and (d) a possible secondary
ozonide from the reaction of ozone with styrene.
Table 5.3 Ar:Ozone:Styrene Merged Jet Product Assignments and Behavior Upon Irradiation
exptl. 16O
exptl. 18O
behavior
new bands
shift (cm-1)
Assignment
-1
-1
(cm )
(cm )
upon irradiation
(cm-1)
746
746
0
+
benzaldehyde
758
758
0
+
benzaldehyde
828
828
0
=
benzaldehyde
0
885
phenyloxirane
0
987
phenyloxirane
1069
+
benzaldehyde
1218
1218
0
=
benzaldehyde
1314
1314
0
+
benzaldehyde
1382
1382
0
+
benzaldehyde
1391
1391
0
+
benzaldehyde
1462
1462
0
+
benzaldehyde
0
1480
acetophenone
0
1698
acetophenone
0
1736
phenylacetaldehyde
1717
1675
-42
+
benzaldehyde
1743
1695
-48
+
formaldehyde
(+) denotes an increase, (=) denotes remained the same. Experimental error ≤ ±1 cm-1.
56
absorptions are valuable when comparing to experimental data. For the primary ozonide, the
cm-1 with a -1 cm-1
18
O shift. The mode with the second greatest
18
O shift with a significant
intensity for the primary ozonide is ascribed to the O-O-O antisymmetric stretching vibration
calculated at 705 cm-1 that shifts -31 cm-1. The characteristic O-O stretch of the two possible
Criegee intermediates were calculated at 910 cm-1 for the benzaldehyde-O-oxide (with a -28 cm-1
shift) and at 901 cm-1 for the formaldehyde-O-oxide (with an -16 cm-1 shift). The most intense
absorption of one secondary ozonide was calculated at 1084 cm-1 with an
18
O shift of -21 cm-1
and is associated with a C-O-C stretching motion. These theoretical calculations were compared
to the experimental observations from twin, and merged jet experiments. Similar calculations for
the final photochemical products were also studied and compared to known spectra in the
literature. Figure S5.4 represents the photochemical products from the twin jet experiments.
Discussion
An important goal in this investigation is to provide experimental evidence for the
reaction mechanism by the direct observation of the early intermediates. Following the Criegee
mechanism for the ozonolysis of styrene, the asymmetrical primary ozonide may decompose in
two ways to form formaldehyde with a benzaldehyde-O-oxide Criegee intermediate as well as
benzaldehyde with a formaldehyde-O-oxide Criegee intermediate. These two pairs can combine
in three ways to form three cross secondary ozonides. None of these species have been observed
experimentally from the ozonolysis of styrene. However, Sander and co-workers generated a
carbonyl oxide by irradiating a synthetic diazo compound that resulted in a triplet state carbene.
This carbene readily reacts with O2 which also has a triplet ground state to generate the
benzaldehyde-O-oxide.2 Matrix isolation coupled to IR spectroscopy was the mode of detection
in these experiments which made it a useful in comparison with the current study.
57
O3 + Styrene Twin Jet. Twin, and merged jet deposition were used to probe different time and
temperature regimes with respect to the mixing and reacting of O3 with styrene. Twin jet allows
for only a brief amount of mixing on the surface of the condensing matrix surface. Upon initial
twin jet deposition into argon matrices at 19 K then annealing to 35 K, two very weak bands
grew in at 763 and 1460 cm-1. Due to the low intensity of these bands,
18
O results from this
experiment were rendered inconclusive. In the twin jet experiments where the reactants were
deposited into an already warm matrix (35 K), the two bands from the aforementioned twin jet
experiment at 763 and 1460 cm-1 were on average 21% more intense while to a variety of new
weak-to-medium bands were observed. After comparison with an authentic benzaldehyde blank
spectra Figure S5.1 (one of the aldehydes expected to form within this mechanism),
benzaldehyde was assigned to the most intense band in this experiment at 1724 cm-1 among other
medium bands. Literature comparisons of this experiment with formaldehyde in an argon matrix
indicated that this second aldehyde is not formed in this experiment.6 Again, the intensity and
broadening of the remaining unassigned bands made it difficult to make assignments based on
18
O labeling experiments.
Next, using krypton as the matrix material, annealing to 68 K resulted in bands that grew
in as parent bands decreased greatly. Some of these bands were similar to those seen in the warm
argon matrix twin jet experiment. Figure 5.2 shows that
18
O labeling was successful and
assignments are made in Table 5.2.
As outlined below, evidence supports the assignment of product absorptions in krypton
experiments to the primary and secondary ozonides of styrene, as well as one of the Criegee
intermediate–carbonyl compound pairs. First, theoretical calculations for the 18O-labeled primary
ozonide predict a characteristic shift pattern of its important vibrations. The most intense
58
calculated band is due to the phenyl ring bending at 716 cm-1 and is expected to shift -1 cm-1.
The experimental band at 761 cm-1 was in agreement with this prediction, with a -2 cm-1
18
O
shift. Next, theoretical bands at 705 and 978 cm-1 are attributed to both the asymmetrical and
symmetrical O-O-O stretching modes and have expected
18
O shifts of -31 and -16 cm-1
respectively. Again, the experimental bands at 684 and 972 cm-1 were in agreement with the
theoretical study, with shifts of -31 and -16 cm-1 respectively. On the basis of correlations
between theoretical isotopic shifts and observations in the krypton twin jet experiments,
assignments to the primary ozonide of styrene are made.
A second key conclusion comes from the comparison between the twin jet krypton matrix
annealed spectra and a blank infrared spectrum of benzaldehyde in argon. This comparison
strongly supports the formation of benzaldehyde and its growth upon annealing to 68 K. All of
the most intense bands of benzaldehyde were observed in the twin jet experiments and showed
the anticipated
18
O shifts. Likewise, comparisons of the krypton matrix experiments with a
literature spectrum of formaldehyde in an argon matrix, led to the conclusion that CH2O is
formed as well.6
One new band in the krypton annealed experiments is of importance due to its occurrence
in the region of the IR spectrum where the anti-symmetric C=O-O stretch for the Criegee
intermediate is expected (about 900 to 1000 cm-1). A product band at 934 cm-1 shifted -13 cm-1
with
18
O labeling. Theoretical data predicts a -16 cm-1
18
O shift for the C=O-O mode of the
formaldehyde-O-oxide Criegee intermediate at 901cm-1 (unscaled). This matches well the
observed band and shift, taking into account that such calculations are typically 3% in error.
Moreover, the theoretical shift for the same band in the benzaldehyde-O-oxide Criegee
intermediate is -28 cm-1, larger than observed experimentally. In addition, the benzaldehyde-O-
59
oxide has been isolated in an argon matrix in the literature using the previous described carbene
route.2 Sander et al. assigned bands for the C=O-O of benzaldehyde-O-oxide at 915 and 890 cm-1
(syn and anti conformations). These bands shifted -30 and -21 cm-1 respectively, with
18
O
labeling. Considering the lack of correlation between the krypton experimental band at 934 cm-1
to what is known in the literature of the benzaldehyde-O-oxide, as well as calculations, it is
concluded that benzaldehyde-O-oxide is not observed here. In contrast, since there is agreement
between the 934 cm-1 band and the formaldehyde-O-oxide, it is likely that this Criegee
intermediate is formed. The observation of both formaldehyde and benzaldehyde in this system
is also consistent with the proposed Criegee mechanism, since the unsymmetrical primary
ozonide can cleave in two different ways leading to the two observed products.7 In this case, it
appears that the benzaldehyde-O-oxide Criegee intermediate may not be observed due rapid
dissociation to benzaldehyde with an O atom rather than recombining with the aldehydes to form
a secondary ozonide. The O atom that resulted may have combined with another in the matrix to
form O2. Another possibility is that the benzaldehyde-O-oxide bands are “hidden” underneath
the styrene parent bands, like many of the remaining fundamental bands for the formaldehyde-Ooxide. It is noteworthy that calculations predict only a single intense band for the Criegee
intermediate, along with a number of quite weak bands. Thus, the observation of a single product
band is in keeping with the prediction of the calculations.
The Criegee mechanism then predicts the formation of a secondary ozonide. Here, three
possible secondary ozonides are explored (Figure S5.3). The theoretical IR spectra for all three
molecules exhibit the most intense vibration for these species due to the asymmetrical C-O-C
stretch of the five memebered ring. All three secondary ozonides exhibit a theoretical C-O-C
stretch at an averaged 1079 cm-1 (unscaled, calculated) with an
60
18
O shift from -21 to -13 cm-1.
Again, the annealed twin jet krypton experimental band at 1058 cm-1 shifts -9 cm-1 and agrees
somewhat to what is expected for a secondary ozonide
18
O shift. Keep in mind that this is a
region of the IR spectrum where the fundamental band (1040 cm-1) for ozone lies and makes it
difficult to make assignments. The phenyl-substituted secondary ozonide also has a moderately
intense C-H wag vibration above 1350 cm-1 (calculated, unscaled) that shifts -1 to -2 cm-1. The
experimental band at 1367 cm-1 that does not shift with
18
O substitution matches well with this
prediction. Since, there is limited diffusion throughout the matrix at this temperature, the
formation of two cross secondary ozonides (SOZ2 and SOZ3 in Figure S5.3), is unlikely.
O3 + Styrene Twin Jet Photochemistry: In annealed twin jet krypton matrix experiments that
were irradiated with λ ≥ 220 nm of light, the matrix was lost due to warming by the Hg arc lamp
and the photochemistry of the assigned early intermediates could not be explored. The
photochemical reaction of ozone with styrene in argon did, however, lead to the series of product
bands listed in Table 5.1. The results are characteristic of the photodetachment of an O atom
from ozone when irradiated and subsequent O atom reaction with styrene.8,9 Researchers have
argued whether or not the O atom reacts with the vinyl or ring double bonds within styrene.9,10
Several of the most intense absorptions detected here can be assigned to literature spectra or
calculated data for phenyloxirane, acetophenone, or phenylacetaldehyde.11 The postulate has
been suggested that for the reaction of O atoms with alkenes, attack occurs at the least
substituted carbon atom in the double bond, leading to either stabilization there and formation of
the appropriate aldehyde (phenylacetaldehyde here) or the formation of a three membered
epoxide ring (phenyloxirane here).8 However, the matrix may make other pathways available,
through steric constraints or rearrangement. For example, the reopening of the epoxide ring can
leave the O atom on either side of the carbon atoms involved in the double bond, hence the
61
acetophenone and phenylacetaldehyde both observed. The evidence here does not support the O
atom attack on the phenyl ring.
O3 + Styrene Merged Jet: In merged jet deposition, the mixing of ozone and styrene in argon
occurred at room temperature in a flow tube outside of the matrix cell. Additional reaction time
is available in this mode compared to twin jet and has led to “late” thermal reaction products in
previous studies.12,13 In these experiments, bands of the early intermediate species assigned in the
krypton matrix twin jet spectra were not present and a number of known final product
absorptions were observed (Table 5.3). This indicates that the early intermediates were short
lived under these conditions and the reaction went further toward completion. In particular, there
were new product bands in the carbonyl stretching region. Product identification can be made
from the known infrared spectra in argon matrices benzaldehyde and formaldehyde. While stable
products were formed, these are consistent with the Criegee mechanism. The observation of both
benzaldehyde and formaldehyde is not only expected from the Criegee mechanism but also may
be the result of the loss of an O atom from the Criegee intermediates or decomposition of
primary and secondary ozonides. In fact, in a similar study, Niki et al. noted that the presence of
these carbonyl compounds in normal gas-phase conditions is a result of further reactions of the
Criegee intermediate and not decomposition of the secondary ozonide.14 Not only do these
results give additional evidence for the Criegee mechanism, but more importantly, they support
the formation and rearrangement of the Criegee intermediate. In addition, photochemistry
revealed a behavior that is consistent with the previous conclusions (i.e. ozone decomposition
and subsequent O atom reaction with vinyl double bond). Assignments based on
18
O shifts,
behavior upon irradiation, and new bands seen in merged jet experiments are listed in Table 5.3.
Conclusions
62
The codeposition of O3 with styrene into krypton has led to the observation of the early
reaction intermediates and stable reaction products. Twin jet deposition followed by warming to
68 K led to new bands assigned to the primary ozonide, secondary ozonide, Criegee
intermediate, formaldehyde, and benzaldehyde. This is the first characterization these early
intermediates using
18
O isotopic labeling and theoretical calculations, along with a direct
comparison to a specific carbonyl oxide (benzaldehyde-O-oxide) characterized in the literature.
Most importantly, the formation and isolation of the Criegee intermediate resulting from a
conjugated alkene increases the overall understanding of the mechanism of the ozonolysis of
alkenes. Likewise, the conclusions from the photochemical reaction refuted what is thought to
occur from a reaction between an O atom and alkene containing more than one double bond.
Irradiation of these matrices resulted in products formed from the O atom attack on the vinyl
double bond of styrene. In contrast, merged jet deposition led to two of carbonyl-containing final
products, thought to be formed from the dissociation of the Criegee intermediate.
Supporting Information
Supplemental spectra, figures and data tables are available in Appendix B.
63
References:
(1)
. (2)
Atkinson, R.; Carter, W. Chem. Rev. 1984, 84, 437.
Sander, W. J. Org. Chem. 1989, 54, 333.
(3)
Andrew, L.; Spiker, R. C. J. Phys. Chem. 1972, 76, 3208.
(4)
McMahon, R. J.; Chapman, O. L. J. Am. Chem. Soc. 1987, 109, 683.
(5)
Gebicki, J.; Kuberski, S; Kaminski, K. J. Chem. Soc. Perkin Trans. 1990, 2, 765.
(6)
Diem, M.; Lee, K. C. J. Phys. Chem. 1982, 86, 4507.
(7)
Bailey, P. Ozonation in Organic Chemistry Olefinic Compounds; Academic Press, Inc.:
New York, 1978.
(8)
Cvetanovic, R. Can. J. Chem. 1958, 36, 623.
(9)
Erhardt, J. M.; Grover, E. R.; Wuest, J. D. J. Am. Chem. Soc. 1980, 102, 6369.
(10)
Sloane, T. M; Brudzynski, R. J. J. Am. Chem. Soc. 1979, 101, 1495.
(11)
Lopes, S.; Gomez-Zavaglia, A.; Lapinski, L.; Fausto, R. J. Phys. Chem. A 2005, 109,
5560.
(12)
Coleman, B. E.; Ault, B. S. J. Phys. Chem. A 2010, 114, 12667.
(13)
Coleman, B. E.; Ault, B. S. J. Mol. Struct. 2010, 976, 249.
(14)
Niki, H.; Savage, C.; Breitenbach, L.; Hurley, M. J. Phys. Chem 1987, 91, 941.
64
Chapter 6
Ozonolysis of Z-3-methyl-2-pentene Using Matrix Isolation Infrared Spectroscopy
Introduction
The room temperature rate constant for the ozonolysis of Z-3-methyl-2-pentene (MP)
(2.75 x 108 cm3 mol-1 s-1) is comparable to the more reactive chain alkene, 2,3-dimethyl-2-butene
(6.99 x 108 cm3 mol-1 s-1).1 This study serves to discover the reactivity of MP under matrix
conditions and to complement previous studies that support the Criegee mechanism.2,3,4 Z-3methyl-2-pentene (MP) is an asymmetrical alkene with electron donating substituents attributed
to its increased reactivity towards ozone when compared to less substituted systems. 5 The
ozonolysis of MP results in the formation of an asymmetric primary ozonide. The primary
ozonide can decompose in two separate ways forming two different Criegee intermediates, with
their carbonyl compound counterparts. If able to diffuse, these pairs can combine to form three
cross secondary ozonides. This work has led to the observation of early intermediates and stable
products for the ozonolysis reaction with MP.
Results
Prior to any deposition experiments, blank experiments were run on each of the parent
reagents used in this study. An acetaldehyde blank spectrum was run for comparison with
experimental spectra. In each case, the blanks were in good agreement with literature spectra.6,7,8
Twin Jet 16O3 + MP: A series of twin jet experiments were conducted with samples of Ar:16O3 =
250 and Ar:MP = 200. In these experiments, several very weak bands grew in upon 24 h of
deposition. The sample was then warmed to 35 K and recooled to 19 K. In Figure 6.1, the bands
in the 24 h deposited experiment grew in intensity and other new bands were observed. These are
65
Figure 6.1 Red trace is the spectrum resulting from the twin jet Ar:O3:MP = 2000:4:5 annealed
to 35 K. Bands that grew in upon annealing are labeled. The blue trace spectrum is Ar:MP =
200:1 upon annealing to 35 K.
66
listed in Table 6.1. The results were reproducible, with the same new bands observed in each
experiment. These matrices were subsequently irradiated for 1.0 h with a quartz filtered (λ ≥ 220
nm) output of a medium-pressure Hg arc lamp leading to the formation of a number of new
bands. Some of the bands that grew in upon annealing decreased slightly. Figure 6.2 shows a
portion of the spectrum where new the bands that grew in and their tentative assignments are
listed in Table 6.2.
Merged Jet 16O3 + MP: Merged jet experiments were completed with Ar:16O3 = 250 and Ar:MP
= 250 at a 1.0 m merged region at room temperature. Parent bands were reduced with the growth
of new bands. Some bands were similar to those observed in the twin jet studies. Figure 6.3
shows the C=O stretch region of one merged jet experiment. Product bands are listed in Table
S6.1.
18
O3 + MP: Twin and merged jet 18O3 labeled experiments were also conducted with M/R ratios
= 250 in argon experiments. Results paralleled those obtained for the normal isotopic species,
with many product bands showing an isotopic red shift relative to the corresponding
experiments. The analogous shifted product bands were slightly less intense than the
16
16
O3
O bands
in table 6.1.
Results of Calculations
To complement the experimental data, DFT calculations were carried out on
intermediates and expected products. Energy minima were located for the optimized structures
and the vibrational spectra were calculated for both normal isotope species in oxygen containing
molecules and
18
O-substituted isotopologues. Calculated structures for the anticipated
intermediates of interest and additional possible products are presented in Figures 6.4. Of
importance are the calculated vibrational frequencies and intensities for the primary ozonide,
67
Table 6.1 Intermediate Bands From the Twin Jet Annealed Ar:O3:MP=2000:4:5
exptl. 16O
calc. 16O
calc. 18O shift
exptl. 18O shift
assignment
721
745
-36
-42
primary ozonide
729
*
781
790
-2
-3
primary ozonide
855
*
859
*
878
*
887
886
-20
-18
primary ozonide
908
940
-4
-4
2-butanone
990
*
994
*
1018
1024
0
secondary ozonide
1055
*
1072
*
1087
*
1094
*
1130
-2
1143
1141
-2
-2
secondary ozonide
1162
*
1191
1209
-1
0
secondary ozonide
1233
*
1332
1362
-2
-2
primary ozonide
1341
0
1346
0
1352
0
CH3 sym bending modes
1367
0
1386
0
1465
0
CH3 asym/CH2 bending mode
1718
-23
acetaldehydehyde/2-butanone
*too weak to determine or shifts into parent bands. Calculated bands completed with DFT
B3LYP 6-311G++d,2p. Theoretical error ±3%. Experimental error ≤ ±1 cm-1.
68
0.47
0.45
0.40
0.35
0.30
A
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.08
1765
1760
Name
1750
1740
1730
cm-1
Description
1720
1710
1700
Figure
6.2 C=O stretch region. Lower trace: twin jet annealed Ar:O3:MP = 2000:4:5. Upper
012412g TJ Ar:16O3:Z-3M2P=2000:4:5, deposited for 24h, annealed to 35K
trace 012412h
is theAr:16O3:Z-3M2P=2000:4:5,
result upon irradiation
for to135K,
h irradiated
at λ ≥for 1h220 nm.
deposited for 24h, annealed
(a)
(b)
(c)
(d)
Figure 6.3 Possible intermediates resulting from the ozonolysis of MP. (a) primary ozonide, (b)
acetaldehyde-O-oxide, (c) butanone-O-oxide, (d) secondary ozonide.
69
1692
Table 6.2 New Bands Resulting from the Twin Jet Photolysis of Ar:O3:MP=2000:4:5
exptl. 16O (cm-1)
calc. 16O
calc. 18O shift
exptl. 18O shift(cm-1)
assignment
784
870
792
888
-1
-5
0
0
MPO
AC
919
937
950
959
1116
1149
1154
1170
1177
1182
1345
*
926
989
1007
-3
-1
-1
-3
-3
0
*
-2
0
*
-5
-5
*
MPO
MPO
1143
-3
1172
1187
-2
-2
1367
-2
CH3 sym bending mode
1382
*
MPO
BN
AC, DB, 23MN, 32MN
BN
*too weak to determine or shifts into parent bands. Calculated bands completed with DFT B3LYP 6311G++d,2p. MPO; 3-methyl-2-pentene oxide, AC; acetaldehyde, BN; 2-butanone, DB; 2,2dimethylbutanal, 32MN; 3-methyl-2-pentanone, 23MN; 2-methyl-3-pentanone. Theoretical error ±3%.
1730
-35
-32
Experimental error ≤ ±1 cm-1.
70
2.1
2.0
1.8
1.6
1.4
A
1.2
1.0
0.8
0.6
0.4
0.2
-0.0
-0.1
3698
3500
3000
Name
Description
020612e
MJ=1m Ar:16O3:Z3M2P= 2000:4:5 dep overnight
012612ecorr Ar:Z-3M2P=200:1 deposited for 24 hrs, annealed to 35K
cm-1
2500
2000
1576
Figure 6.4 Black trace shows select region of a merged jet (1 m) Ar: 2000:4:5 experiment. Blue
trace is an Ar: MP = 200:1 blank.
71
Criegee intermediates, and secondary ozonides. They are listed in Table S6.2. In addition to the
fundamental absorptions for each species, the calculated
18
O shifts of the most intense most
intense absorption gives structural information. The most intense band for the primary ozonide is
ascribed to the O-O-O antisymmetric stretching vibration calculated at 745 cm-1 that shifts -36
cm-1. The characteristic C=O-O stretch of two possible Criegee intermediate structures were
calculated at 902 cm-1 for the butanone-O-oxide (with a -42 cm-1 shift) and at 962 cm-1 for the
acetaldehyde-O-oxide (with an -19 cm-1 shift). The most intense absorption for one secondary
ozonide was calculated at 1117 cm-1 with an 18O shift of -10 cm-1 and is associated with a C-O-C
stretching motion. These theoretical calculations were compared to the experimental
observations from experiments. Similar calculations for the final photochemical products were
also studied and compared to known spectra in the literature. Figure S6.1 represents the
photochemical products from the twin jet experiments.
Discussion
Following the Criegee mechanism for the ozonolysis of MP, the asymmetrical primary
ozonide may decompose in two ways to form acetaldehyde with a butanone-O-oxide Criegee
intermediate as well as butanone with an acetaldehyde-O-oxide Criegee intermediate. These can
combine to form secondary ozonides. None of these species have been observed previously for
the ozonolysis of MP. However, previous studies involving the ozonolysis of an asymmetrical
alkene have observed two different Criegee intermediates.4
O3 + MP Twin Jet. Twin, and merged jet deposition were used to probe different time and
temperature regimes with respect to the mixing and reacting of O3 with MP. Twin jet allows for
only a brief amount of mixing on the surface of the condensing matrix surface. Upon initial twin
jet deposition into argon matrices at 19 K, very weak bands that grew in are considered
72
intermediate bands. It is known that behavior of these bands upon annealing, irradiation, and
isotopic labeling give additional structural information.2,3,4
Evidence here supports the assignment of new absorptions in the twin jet annealed
experiments to the primary and secondary ozonides of MP. Theoretical calculations for the 18Olabeled intermediates predict a characteristic shift pattern of their vibrations. For the POZ, the
most intense calculated band due to the O-O-O stretching mode is at 745 cm-1 and shifts -36 cm-1
upon
18
O labeling. The experimental band at 721 cm-1 that shifts -42 cm-1 upon
18
O labeling
agrees with the POZ theoretical band position and shift. Additional fundamentals for the POZ are
assigned in Table 6.1. Although not assigned here, there is indirect evidence that supports the
formation of the Criegee intermediates of MP. Adapting the Criegee mechanism to MP, two
carbonyl compounds (acetaldehyde and 2-butanone) are formed as pairs with the Criegee
intermediates. The comparison of an authentic acetaldehyde in argon spectrum with one twin jet
experiment in Figure S6.2 supports acetaldehyde formation. In the twin jet annealed experiment,
the broad C=O stretch absorption centered at 1718 cm-1 also fits for 2-butanone which has its
C=O stretching mode at 1730 cm-1.9 For the two Criegee intermediates paired with the carbonyl
compounds, theoretical calculations predict C=O-O stretching modes at 902 and 962 cm-1 for the
butanone-O-oxide and acetaldehyde-O-oxide respectively. In Table 6.1 several experimental
bands ranging from 800 to 1000 cm-1 have immeasurable
18
O shifts due to either shifting into
parent bands or are too weak in intensity. It is likely some of these bands belong to the Criegee
intermediates. Likewise, the theoretical C-O-C stretching mode at 1117 cm-1 for the SOZ is not
assigned in the twin jet annealed experiments. Again, it is possible that the most intense
experimental band for the SOZ is not observed due to overlapping with parent bands.
Nonetheless, less intense fundamentals for the SOZ are assigned in Table 6.1. Since, there is
73
limited diffusion throughout the matrix at this temperature; the formation of cross secondary
ozonides is unlikely. The assignments here suggest the Criegee mechanism is followed for MP.
This work has yielded the first definite assignment of IR bands for the POZ and SOZ of MP, as
well as indirect evidence for the CI.
O3 + MP Twin Jet Photochemistry The photochemical reaction of ozone with MP lead to the
series of bands listed in Table 6.2. The results are characteristic of the photo-detachment of an O
atom from ozone when irradiated and subsequent O atom reaction with MP.10 The very broad
C=O stretching absorption centered at 1730 cm-1 can be assigned to literature spectra or
calculated data for acetaldehyde, 2-butanone, 3-methyl-2-pentanone, 2-methyl-3-pentanone, and
2-2-dimethylbutanal.8,9,11 Many of the carbonyl compound photo-products share structural
similarities that render it difficult to assign specific vibrations for each. It is known that for the
reaction of O atoms with alkenes, attack occurs at the least substituted carbon atom in the double
bond, leading to either stabilization there and formation of the appropriate carbonyl compound
(3-methyl-2-butanone and 2-2-dimethylbutanal here) or the formation of a three membered
epoxide ring (3-methyl-2-pentene oxide).10 The matrix may make other pathways available,
through steric constraints or rearrangement. For example, the reopening of the epoxide ring can
leave the O atom on either side of the carbon atoms involved in the double bond, hence 2methyl-3-pentanone. Similar to the twin jet experiments, several of the
18
O shifts for photo
products were not observed. It is concluded that the photo reaction is dominated by the O-atom
reaction with MP.
O3 + MP Merged Jet: In merged jet deposition, the mixing of O3 and MP in argon occurred at
room temperature in a 1 m flow tube outside of the matrix cell. Additional reaction time is
available in this mode compared to twin jet and has led to “late” thermal reaction products in
74
previous studies.2,3,4 In this study, the fundamental for O3 at 1040 cm-1 was completely
diminished and the MP fundamentals decrease greatly suggesting an extensive reaction through
the 1 m merged jet region. Merged jet product 16O bands and 18O shifts are listed in Table S6.1.
Like in the twin jet irradiated experiments, assignments for these bands are difficult due the
similarities in the products formed. However, there are several key spectral features that are
indicative of specific species. There is an intense broad feature centered at 1719 cm-1 that ranges
from 1680-1750 cm-1. This band is characteristic of a C=O stretching mode. Also, there is a very
broad O-H stretching band at 3411 cm-1. These two features together suggest the formation of a
carboxylic acid or ketol. In a study involving the merged jet ozonolysis of 2,3-dimethyl-2butene, a rearrangement of the Criegee intermediate resulted in the formation of
hydroxyacetone.3 Adapting the Criegee intermediate rearrangement mechanism here, specific
identifications can be made for acetoin, and glycolaldehyde.12,13 It is concluded that the
absorptions that resulted here are due to primary and secondary reactions of O3 with MP and are
considered final reaction products.
Conclusions
The codeposition of O3 with MP in an argon matrix yielded reaction intermediates and
stable reaction products. Twin jet deposition followed by warming to 35K led to new bands
assigned to the primary ozonide and secondary ozonide, as well as acetaldehyde, and 2-butanone.
This is the first characterization these early intermediates using this matrix isolation. The
conclusions from the photo-reaction were consistent with what is known of the photo-reaction
between O-atoms and alkenes. In contrast, merged jet deposition resulted in carbonyl-type final
products, two thought to be formed from the rearrangement of the Criegee intermediates.
75
Supporting Information
Supplemental spectra, figures and data tables are available in Appendix C.
76
References:
(1)
Atkinson, R.; Carter, W. Chem. Rev. 1984, 84, 437.
(2)
Coleman, B. E.; Ault, B. S. J. Mol. Struct. 2010, 976, 249.
(3)
Coleman, B. E.; Ault, B. S. J. Phys. Chem. A 2010, 114, 12667.
(4)
Coleman, B. E.; Ault, B. S. J. Mol. Struct. 2012, in press.
(5)
Bailey, P. Ozonation in Organic Chemistry Olefinic Compounds; Academic Press, Inc.:
New York, 1978.
(6)
Andrews, L.; Spiker, R. C. J. Phys. Chem. 1972, 76, 3208.
(7)
Coleman,W; Gordon, B. J. Appl. Spectrosc. 1988, 42, 666.
(8)
Vedova, C. D.; Sala, O. J. Raman Spectrosc. 1991, 22, 505.
(9)
Limberg C.; Koppe, R. Inorg. Chem. 1999, 38, 2106.
(10)
Cvetanovic, R. Can. J. Chem. 1958, 36, 623.
(11)
Coleman,W; Gordon, B. J. Appl. Spectrosc. 1987, 41, 1159.
(12)
Coleman,W; Gordon, B. J. Appl. Spectrosc. 1989, 43, 305.
(13)
Bennett. C.; Kaiser, R. The Astrophysical Journal, 2007, 661, 899.
77
Chapter 7
Theoretical Relative Energies for the Intermediates from the Ozonolysis of Alkenes
POZ
CI1
CI2
SOZ
Figure 7.1 Intermediates from the ozonolysis of propene.
Table 7.1 Relative Zero Point Energies for the Intermediates in the Ozonolysis of
Propene
Species
Relative E(kcal mol-1)
O3 + Propene
0.0
POZ
-50.7
CI1 + formaldehyde
-10.6
CI2 + acetaldehyde
-11.2
SOZ
-56.5
Calculated using DFT B3LYP 6-311G++(d,2p). Theoretical error ±4 kcal mol-1.
78
POZ
CI
SOZ
Figure 7.2 Intermediates from the ozonolysis of 2,3-dimethyl-2-butene.
Table 7.2 Relative Zero Point Energies for the Intermediates in the Ozonolysis of 2,3dimethyl-2-butene
Species
Relative E(kcal mol-1)
O3 + DMB
0.0
POZ
-58.7
CI1 + acetone
-86.6
SOZ
-117.9
Calculated using DFT B3LYP 6-311G++(d,2p). Theoretical error ±4 kcal mol-1.
79
POZ
TS1
TS2
synCI
antiCI
SOZ1
SOZ2
Figure 7.3 Intermediates from the ozonolysis of styrene.
80
Table 7.3 Relative Zero Point Energies for the Intermediates in the Ozonolysis of
Styrene
Species
Relative E(kcal mol-1)
O3 + Styrene
0.0
POZ
-53.9
TS2
-40.9
TS1
-37.9
CI1 + benzaldehyde
-62.9
synCI2 + formaldehyde
-65.0
antiCI2 + formaldehyde
-64.2
SOZ1
-101.2
SOZ2
-102.5
Calculated using DFT B3LYP 6-311G++(d,2p). Theoretical error ±4 kcal mol-1.
81
CI1
CI4
CI2
CI3
CI5
CI6
CI7
CI8
CI9
SOZ
POZ
Figure 7.4 Intermediates from the ozonolysis of Z-3-methyl-2-pentene.
82
Table 7.4 Relative Zero Point Energies for the Intermediates in the Ozonolysis of
Z-3-methyl-2-pentene
Species
Relative E(kcal mol-1)
O3 + Z-3-methyl-2-pentene
0.0
POZ
-58.4
CI1 + acetaldehyde
-79.1
CI2 + 2-butanone
-76.0
CI3 + acetaldehyde
-78.6
CI4 + acetaldehyde
-77.2
CI5 + acetaldehyde
-72.2
CI6 + acetaldedyde
-68.9
CI7 + acetaldehyde
-72.2
CI8 + acetaldehyde
-71.2
CI9 + acetaldehyde
-77.0
SOZ
-112.5
Calculated using DFT B3LYP 6-311G++(d,2p). Theoretical error ±4 kcal mol-1.
83
Table 7.5 Benchmark Calculations for C=O Stretch 18O Isotopic Shifts Compared to
Experimental Values
DFT
DFT
DFT
DFT
B3PW91
MP2 6- MP2 6B3LYP 6B3LYP 6- B3PW91 6method
6311++( 311++(3
311++(d,2
311++(3df, 311++(3df,3
311++(d,2
d,2p)
df,3pd)
p)
3pd)
pd)
p)
formaldehyde
theoretical shift
-37
-39
-37
-39
-31
-32
Ar matrix shift
-39
-39
-39
-39
-39
-39
difference
(theoretical shift-2
0
-2
0
-8
-7
experimental
shift)
acetaldehyde
theoretical shift
-36
-37
-36
-37
-34
-34
Ar matrix shift
-34
-34
-34
-34
-34
-34
difference
(theoretical shift-2
-3
-2
-3
0
0
experimental
shift)
acetone
theoretical shift
-35
-35
-35
-35
-32
-33
Ar matrix shift
-33
-33
-33
-33
-33
-33
difference
(theoretical shift-2
-2
-2
-2
1
0
experimental
shift)
84
Chapter 8
Overall Conclusion
Matrix isolation using twin jet deposition and annealing has proven useful for sufficient
control of the excess energy to permit observation of the long sought after early intermediates in
these systems. There is direct and indirect evidence that the Criegee mechanism is followed for
the ozonolysis of propene, 2,3-dimethyl-2-butene, styrene, and Z-3-methyl-2-pentene.
Previously, the infrared spectra for the many of the intermediates for these alkenes were
unknown. This study has shed light on this mechanism that is accepted but often scrutinized. In
addition, the photo-reactions in these systems are some of few that have used O3 as an O-atom
source for a reaction with alkenes.
Future Work
The Ault research group will continue to expand this project to more complex systems
such as cyclic and bicyclic alkenes as well as cyclic dienes. In addition, it would be useful to
explore other mechanisms involved in atmospheric chemistry using matrix isolation. The
ozonolysis of alkenes has only scratched the surface when beginning to understand the complex
mixing reactor we call our atmosphere.
85
Appendix A
Supporting Information for:
“Investigation of the Thermal and Photochemical Reactions of Ozone with
2,3-dimethyl-2-Butene (DMB) Using Matrix Isolation”
a)
b)
c)
d)
e)
f)
Figure S4.1 Calculated structures for a) hydroxyacetone, b) dimethyldioxirane, c)
tetramethyloxirane, d) 3,3-dimethyl-2-butanone, e) methyl acetate, f) acetone.
86
2000 1900 1800 1700 1600 1500 1400 1300
1200 1100 1000 900
800 711
Wavenumbers (cm-1)
Figure S4.2 Blue trace is the IR spectra of twin jet deposited Ar: O3:DMB =500:1:1 irradiated
for 1 h with λ ≥ 220nm. Black trace is the same experiment, however with O2 used as the host
gas.
87
3600
3200
2800
2400
2000
1800
1600
-1
Wavenumbers (cm )
Figure S4.3 Black trace is the IR spectrum of merged jet (2 m) Ar: O3:DMB = 500:1:1. Below is
Ar:DMB = 250:1.
a)
1730
b)
1695
c)
1206
Wavenumbers (cm-1)
732
719
Figure S4.4 Representative IR spectra regions for a) acetone, b) secondary ozonide, and c)
primary ozonide using the concentric jet mode with Ar: O3:DMB = 500:1:1 in both red and black
traces. Black trace is with d = -1 cm and red trace is with d = -6 cm. Intensities are not to scale
(regions are enlarged to show detail).
88
*
18,16
18,18 *
16,18
16,16
885
880
875
870
865
860
855
850
845
840
835
830
825
Figure S4.5 Infrared spectrum from 825 to 885 cm-1 arising from the twin jet deposited Ar:DMB
= 250 with a sample of Ar:16,18O3 = 250 and annealed to 35 K. The features noted with an
asterisk (*) are of the primary ozonide isotopomers. Labeled bands are assigned to the Criegee
intermediate isotopomers.
89
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
-0.2
1800 1700 1600 1500 1400 1300 1200 1100 1000 900
Wavenumbers(cm-1)
800
700
600
500
S4.6 Black trace is the IR spectrum of twin jet deposited Ar:O3:DMB = 500:1:1 annealed to 35
K. Blue trace is IR spectrum of blank Ar:acetone = 250:1.
90
2.4
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
3600
3200
2800
2400
2000 1800 1600
1400
Wavenumbers (cm-1)
1200
1000
800
Figure S4.7 Blue trace is the IR spectrum of twin jet deposited O2:DMB:O3 = 500:1:1 irradiated
at λ ≥ 220nm. Red trace is IR spectrum of blank Ar: hydroxyacetone = 250:1.
91
Figure S4.8 Unimolecular stabilization pathways for the Criegee intermediate.
92
Table S4.1 Calculateda Bandsb and Intensitiesc for the Intermediates Formed in DMB
Thermal Reaction with Ozone
Primary Ozonide
Criegee Intermediate
Secondary Ozonide
freq
18
O shift
int
freq
18
O shift
int
freq
18
O shift
int
20
-1
0
151
0
0
78
-1
2
215
0
0
173
0
1
180
-1
0
244
0
0
274
-8
1
187
-2
0
267
-4
0
305
-8
8
188
0
1
275
-2
0
361
-3
8
225
0
1
283
-1
1
477
-9
0
235
0
0
293
-4
1
596
-17
7
281
-5
4
309
-4
1
811
-11
0
306
0
0
340
-2
1
910
-44
74
354
-11
2
360
-4
1
932
-1
0
367
-6
0
388
-2
1
983
0
8
371
-6
3
449
-13
2
1067
-16
19
453
-9
0
471
-7
4
1089
0
5
509
-11
3
523
-10
4
1306
-1
19
525
-13
19
581
-9
1
1396
-1
33
611
-4
0
647
-7
3
1410
0
5
649
-16
3
689
-27
8
1440
1
7
811
-41
0
760
-40
34
1460
-6
31
827
-31
9
841
-24
4
1473
0
14
848
-20
11
865
-25
14
1480
0
9
854
-17
32
93
924
-46
3
1557
-15
7
902
-46
0
933
-2
0
3010
8
0
932
0
2
938
-1
1
3023
0
14
935
-3
1
952
-4
4
3058
0
1
966
-2
1
958
-3
6
3065
0
5
1007
-15
113
1017
0
0
3133
0
2
1008
-1
0
1025
-1
0
3135
0
9
1010
-3
7
1160
-2
26
1131
-1
8
1177
-2
17
1223
-4
251
1184
-1
27
1229
-3
53
1224
-1
21
1236
-1
5
1266
-1
2
1258
-2
70
1272
-1
4
1275
0
6
1403
-1
2
1402
0
0
1409
0
24
1403
0
58
1419
0
10
1414
0
28
1430
0
0
1417
0
3
1476
0
1
1479
0
0
1490
0
10
1482
0
0
1491
0
8
1482
0
2
1493
0
5
1483
0
1
1509
0
8
1495
0
1
1512
0
4
1500
0
1
94
1514
0
14
1502
0
2
1532
0
6
1508
0
14
3035
0
16
3042
0
0
3041
0
9
3042
0
20
3045
0
19
3049
0
23
3050
0
2
3050
-1
1
3094
0
25
3106
0
7
3101
0
9
3106
0
3
3102
0
26
3117
0
6
3109
0
10
3117
0
32
3123
0
13
3126
0
2
3125
0
16
3126
0
24
3132
0
16
3130
0
30
3137
0
16
3130
0
1
a
Calculated at the B3LYP/6-311G++(d,2p) level. bFrequencies in cm-1. cIntensities in km
mol-1.
95
Table S4.2 Key Structural Parameters Calculateda for the Criegee Intermediate of DMB
Criegee Intermediate
Acetone
parameterb
type
calculated value
calculated value
A(1, 2, 3)
C=O-O
117.77°
-
A(8, 1, 2)
C-C=O
119.53°
121.72°
R(1,2)
C=O
1.267 Å
1.211 Å
R(2, 3)
O-O
1.384 Å
-
a
Calculated at the B3LYP/6-311G(d,2p) level. bSee Figure 7.2 (CI) for atom
numbering.
Table S4.3 Product Intensities in Concentric Jet Experiments as a Function of d
d, cm
I(729 cm-1)
I(1712,1718 cm-1)
I(1206cm-1)
0
0.41
0.12
shoulder
-1
0.63
0.29
0.04
-6
0.34
0.20
0.06
-11
0.33
0.12
0.02
-32*
0.23
shoulder
-
*From merged jet length = 32 cm.
96
Appendix B
Supporting Information for:
“Investigation of the Thermal and Photochemical Reactions of Ozone with Styrene in Argon
and Krypton Matrices”
Figure S5.1 Region of the infrared spectrum of a matrix formed by the (red trace) twin jet
deposition of a sample of Ar:16O3 = 250 with a sample of Ar: styrene = 250 into a 35 K matrix
for 19 h. Green trace a blank Ar:benzaldehyde sample deposited for 24 hrs. New product bands
are labeled in blue.
97
Figure S5.2 Regions of the infrared spectrum of a matrix formed by the (red trace) 2 m merged
jet deposition of a sample of Ar:16O3 = 250 with a sample of Ar: styrene = 250 deposited for 19
h. For comparison, in purple is the ozone blank spectrum and the black trace is a styrene blank.
New product bands are labeled in blue.
Figure S5.3 Calculated structures for the (a) secondary ozonide 1 (SOZ1), (b) secondary ozonide
2 (SOZ2), and (c) secondary ozonide 3 (SOZ3) using the 6-311G++(d,2p) basis set.
98
Figure S5.4 Calculated structures for the photo products (a) phenyloxirane, (b)
phenylacetaldehyde, and (c) acetophenone using the 6-311G++(d,2p) basis set.
Table S5.1 Band Assignments from Twin Jet 35 K Deposited Ar:O3:Styrene =
500:1:1
16
18
O3
O3
Shift
Assignment
676
disappeared
689
689
0
benzaldehyde
751
751
0
benzaldehyde
763
762
-1
830
disappeared
benzaldehyde
924
924
0
936
disappeared
1062
1044
-18
1168
1168
0
benzaldehyde
1313
1313
0
benzaldehyde
1368
1368
0
1457
1457
0
benzaldehyde
1697
1671
-26
benzaldehyde
1724
1692
-32
benzaldehyde
Assignments made by comparison to authentic Ar:benzaldehyde blank spectra.
Table S5.2 Calculated Frequencies, Intensites and Isotopic Shifts for Intermediates
and Photo Products
Primary Ozonide
Criegee Intermediate 1
Criegee Intermediate 2
18
18
freq.
O shift int. freq.
O shift int.
freq. 18O shift
int.
40
-1
2
88
-2
4
529
-18
0
70
-3
6
159
-3
1
668
-8
5
118
-2
4
217
-5
6
901
-16
100
206
-3
4
318
-10
2
941
-1
36
301
-3
2
401
-5
0
1246
-13
16
333
-8
6
412
0
0
1402
-24
15
99
409
413
542
606
632
664
705
716
747
777
813
861
903
933
942
978
993
1010
1012
1018
1050
1072
1112
1183
1203
1222
1241
1293
1312
1346
1353
1390
1486
1502
1527
1626
1644
3053
3070
3129
3152
-17
0
-2
-9
-1
-22
-31
-1
-24
-2
-8
-5
-42
-2
-8
-16
0
-13
-2
0
0
-3
0
0
0
0
-5
-2
-1
-1
0
0
0
-1
0
0
0
0
0
0
0
6
0
27
40
0
6
69
100
17
60
17
0
17
2
50
83
0
0
6
0
4
4
8
0
2
17
2
2
10
4
6
17
19
10
13
0
2
38
25
19
15
481
546
630
684
730
765
851
863
880
910
960
1005
1011
1024
1045
1104
1186
1199
1227
1345
1353
1394
1470
1511
1547
1602
1635
3161
3165
3170
3183
3192
3276
-10
-5
0
0
-12
0
-25
0
-1
-28
-1
0
0
0
0
-1
0
0
-4
-5
-2
-17
-2
-1
-8
0
0
0
0
0
-1
0
-34
5
12
0
18
3
26
26
1
9
100
3
0
1
0
3
4
1
11
12
13
8
3
17
3
34
0
14
1
3
3
8
6
6
100
1534
3115
3269
-12
-1
-1
28
4
1
3164
3173
3182
3190
0
0
0
0
0
23
29
21
Secondary Ozonide 1
freq. 18O shift int.
26
0
0
76
-1
1
154
-2
2
192
-4
0
293
-7
4
362
-10
1
412
0
0
459
-7
1
475
-8
0
632
-8
7
633
0
0
710
-12
0
727
-17
5
746
-9
28
778
-26
1
843
-42
3
864
0
0
877
-8
3
926
-22
3
949
-2
3
976
-13
35
997
0
0
1010
0
0
1018
-1
0
1031
-11
11
1051
-3
8
1084
-21
100
1104
-1
5
1146
-5
3
1182
0
0
1200
0
4
1228
-6
17
1231
-3
8
Secondary Ozonide 2
freq. 18O shift int.
162
-3
11
376
-13
4
710
-31
1
749
-35
1
843
-45
7
925
-24
4
951
-16
45
1035
-17
17
1087
-27
100
1140
-6
6
1143
-5
0
1222
-8
2
1227
-5
2
1373
-6
3
1416
-2
4
1517
0
1
1527
0
0
3022
0
72
3024
0
0
3104
0
18
3105
0
0
101
freq.
25
26
48
55
132
133
243
253
275
321
331
407
414
414
517
546
632
633
645
656
706
710
713
745
771
773
848
858
859
860
884
921
937
Secondary Ozonide 3
O shift
int.
0
0
-1
0
0
0
-3
0
-1
0
-6
0
-2
2
-3
0
-12
0
-8
2
-8
0
0
0
0
0
-2
0
-6
4
0
0
-1
0
-2
0
-3
1
-28
15
-2
10
-2
32
-31
1
-3
2
-3
46
-26
3
-14
2
0
2
-1
0
-17
0
-11
1
-2
9
-8
6
18
1282
1339
1352
1357
1401
1480
1522
1526
1625
1645
3020
3045
3108
3159
3168
3178
3187
3197
-4
-1
0
-1
-2
0
-1
0
0
0
0
0
0
0
0
0
0
0
1
4
13
28
2
4
0
1
0
0
43
7
6
0
2
7
7
2
963
992
993
1004
1010
1011
1019
1020
1045
1048
1057
1067
1108
1113
1183
1183
1198
1200
1230
1234
1322
1330
1331
1350
1352
1353
1403
1423
1488
1491
1529
1529
1630
1630
1646
1647
3021
3023
3159
3159
3166
102
0
-1
-8
1
0
0
-1
-8
-10
-6
-13
0
-3
0
0
1
0
-1
0
-3
-3
-2
-2
0
-1
-1
0
0
1
0
0
0
0
0
-1
0
0
0
0
0
0
16
0
0
6
0
0
2
0
40
10
18
100
0
21
0
0
7
0
28
0
3
1
36
5
4
0
48
1
14
0
1
0
0
0
1
0
0
37
0
1
0
3166
3176
3176
3187
3187
3195
3195
Phenyloxirane
freq. 18O shift int.
59
-1
8
147
-1
5
195
-5
10
335
0
3
397
-8
5
415
0
0
543
-2
31
586
-2
21
633
0
0
713
0
95
763
-2
28
771
-1
100
848
-11
54
862
-1
0
896
-18
95
931
0
5
992
0
0
1003
-3
33
1008
0
3
1017
0
0
1049
0
10
1089
-1
8
1102
0
8
1145
-3
5
1169
-4
3
1182
0
0
1199
0
0
1219
-1
10
1283
-5
18
1332
-1
10
Phenylacetaldehyde
freq. 18O shift int.
34
0
1
56
-2
3
140
0
1
290
-1
1
329
-1
1
415
0
0
441
-7
2
519
-1
12
584
-2
0
636
0
0
715
0
15
762
-1
3
774
-1
7
849
-2
1
860
0
0
929
0
0
992
0
0
1009
-1
1
1009
0
0
1019
0
0
1050
0
7
1054
-1
10
1109
0
3
1182
0
0
1196
-1
6
1205
0
0
1216
0
0
1297
0
1
1337
0
0
1362
0
0
103
freq.
57
153
159
218
365
411
431
465
596
601
632
704
741
775
864
950
957
1003
1017
1017
1045
1047
1093
1106
1183
1200
1273
1336
1353
1392
0
0
0
0
0
0
18
Acetophenone
O shift
0
-1
0
-2
-6
0
-1
-8
-8
-1
0
0
-3
0
0
0
-5
0
0
0
0
-2
-1
0
0
0
-1
-1
0
0
1
10
4
18
0
4
0
int.
2
0
0
2
0
0
0
0
12
6
0
18
0
19
0
1
17
0
0
0
3
0
0
3
0
8
86
3
1
22
1352
1
3 1414
-6
1
1476
-1
1418
-1
33 1469
0
3
1479
-1
1485
0
18 1484
0
2
1485
0
1522
-1
18 1527
0
6
1521
0
1529
0
21 1623
0
1
1619
-2
1624
0
0 1642
0
3
1638
-1
1645
0
13 1798
-37
100 1746
-33
3080
0
77 2882
1
30
3033
0
3105
0
46 3022
0
4
3088
0
3152
0
18 3095
0
3
3139
0
3162
0
0 3153
0
2
3161
0
3170
0
59 3158
0
1
3172
0
3172
0
44 3168
0
2
3182
0
3183
0
38 3177
0
8
3191
0
3189
0
23 3188
1
4
3197
0
Calculated using the 6-311G++(d,2p) basis set. Frequency in cm-1.
104
6
8
5
0
4
11
100
3
7
11
0
7
15
10
6
Appendix C
Supporting Information for:
“Ozonolysis of Z-3-methyl-2-pentene Using Matrix Isolation Infrared Spectroscopy”
(a)
(b)
(c)
(d)
Figure S6.1 Photo-products from the O-atom reaction with MP. (a) 3-methyl-2-pentanone
(32MP), (b) 2,2-dimethylbutanal (DB), (c) 2-methyl-3-pentanone (23MP), (d) 3-methyl-2pentene oxide (MPO).
0.50
0.45
0.40
0.35
0.30
A
0.25
0.20
0.15
0.10
0.05
0.00
-0.05
-0.09
1924
1800
Name
1600
Description
cm-1
1400
1200
scan 2 is an acetaldehyde blank spectrum. Red is a twin jet Ar:O :MP =
Figure 061708b
S6.2 Acetaldehyde
Black trace
3
012412g TJ Ar:16O3:Z-3M2P=2000:4:5, deposited for 24h, annealed to 35K
2000:4:5 annealed spectrum.
105
Table S6.1 Bands resulting from the Merged Jet 1 m Ar: O3:MP= 2000:4:5
exptl. 16O (cm-1)
exptl. 18O shift (cm-1)
710
722
767
854
885
941
991
1135
1160
1181
1221
1241
1347
1498
1719
2128
2230
2273
3411
*shifts into parent or other product bands.
-33
*
0
0
-18
0
0
0
0
0
0
0
0
-13
-28
-25
-9
0
*
Table S6.2 Calculated Frequencies, Intensites and Isotopic Shifts for Intermediates
Primary Ozonide
Criegee Intermediate 1
Secondary Ozonide
freq.
47
106
189
213
225
229
285
301
327
346
454
471
18
O shift
-1
0
-3
0
0
-1
-4
-6
-3
-4
-9
-15
int.
freq.
2
0
0
0
0
0
1
0
1
1
1
7
70
161
199
208
306
344
387
522
603
790
795
902
18
O shift
-2
-2
-1
-1
-8
-9
-7
-7
-12
-8
-3
-42
106
int.
freq.
4
0
2
2
7
2
6
2
4
2
1
83
64
91
185
207
219
236
256
316
366
370
441
509
18
O shift
-1
-1
-2
-3
0
-1
-2
-3
-9
-6
-9
-14
int.
1
1
0
3
0
0
0
0
2
2
6
7
511
622
696
716
745
790
881
886
913
928
1000
1007
1040
1076
1101
1156
1180
1204
1234
1321
1362
1378
1390
1412
1418
1420
1479
1490
1495
1501
1511
1514
1514
3021
3026
3031
3035
3046
3069
3091
-5
-8
-29
-13
-36
-2
-17
-20
-35
-16
-1
0
-1
-1
-4
-5
-2
-1
-1
0
-2
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
2
1
6
5
36
1
8
12
1
2
16
4
7
6
15
7
7
7
5
3
4
0
4
12
4
11
2
9
3
9
8
3
8
20
13
27
22
16
3
24
978
-4
13
991
-1
3
1018
-5
0
1081
-3
19
1108
-6
6
1268
-1
6
1302
-2
8
1351
0
3
1397
-1
30
1417
0
2
1439
0
8
1476
-1
14
1482
-1
5
1504
0
11
1512
-1
12
1543
-18
10
3018
0
5
3022
-1
14
3037
0
22
3058
0
1
3085
0
0
3105
0
23
3109
0
20
3134
0
9
Criegee Intermediate 2
18
freq.
O shift
int.
156
0
1
256
-9
0
323
-8
11
553
-17
9
863
-13
11
886
-27
33
962
-19
109
1062
-1
0
1157
-2
5
1348
-15
13
1418
-2
14
1462
-3
13
1466
0
13
1574
-16
1
107
509
636
733
782
805
846
881
889
904
941
1007
1024
1055
1070
1117
1141
1155
1209
1252
1319
1321
1371
1386
1410
1413
1420
1482
1487
1491
1492
1499
1510
1515
3036
3039
3043
3046
3049
3078
3094
-12
-11
-18
-15
-25
-30
-41
-16
-15
-10
0
-4
-2
-2
-10
-2
-3
-1
-1
-3
0
0
-1
0
-1
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
10
2
1
1
3
4
5
6
28
22
4
36
8
21
209
17
12
58
35
13
23
3
8
52
18
5
1
6
1
2
9
8
6
21
9
18
26
9
2
29
3095
0
24 3017
0
3103
0
9
3059
0
3106
0
27 3129
0
3121
0
18 3142
0
3128
0
19
Calculated with DFT B3LYP 6-311G++(d,2p).
108
3
3
1
6
3105
3106
3115
3123
3127
0
0
0
0
0
12
36
14
18
13
Addendum
Alternate Route to the Criegee Intermediate
The following summarizes efforts towards Sander’s1 synthetic route for the generation of
the benzaldehyde-O-oxide. Synthetic procedure was conducted and written by Sujan Sarkar, a
2nd year graduate student in Anna Gudmundsdottir’s research group:
Reaction scheme:
Preparation of benzaldehyde tosylhydrazone (1):
In a 100 mL round bottomed flask benzaldehyde (4.0 g, 0.037 mol) was stirred with 50 mL of
absolute ethanol. To this stirred solution p-toluenesulfonhydrazide (7.65 g, 0.041 mol) was added
and the resulting mixture was refluxed for 5 h under the atmosphere of Ar. The reaction mixture
was cooled to room temperature and in an ice bath resulting formation of white crystalline solid
out of the reaction mixture. The white solid was filtered and washed with cold absolute ethanol.
The product was recrystallized from hot ethanol to yield pure crystalline product (8.21 g, 0.030
mol, 81% yield).
1
H NMR (DMSO-d6, 400 MHz): δ 11.44 (s, 1H), 7.91 (s, 1H), 7.77-7.75 (d, J = 8.4 Hz, 2H),
7.56 -7.54 (m, 2H), 7.42 -7.38 (m, 5H), 2.36 (s, 3H) ppm. IR (KBr) υmax: 3417 (N-H), 1660
(C=N), 1315 (S=O) cm-1. Mp 128 - 131 °C (lit. 127-128 °C).
109
104.3
100
95
2598.88
3934.65
2312.38
1905.98
1974.39
90
2150.54
1166.22
85
80
75
901.35
70
2917.41
65
3004.12
%R 60
1315.93
55
50
1659.84
1651.74
45
1407.34
1437.20
40
672.78
706.96
35
30
1022.09
953.40
3417.67
25
19.1
4000.0
3600
3200
2800
2400
2000
1800
cm-1
1600
1400
1200
1000
800
600
450.0
Preparation of sodium salt of benzaldehyde tosylhydrazone (2):
Benzaldehyde tosylhydrazone (3.0 g, 0.011 mol) was placed in a 100 mL Erlenmeyer flask and
dissolved in 60 mL of anhydrous diethyl ether and the solution stored in ice bath. To the solution
was added NaH (60% in mineral oil, 0.264 g, 0.011 mol) and the resulting reaction mixture was
stirred for 24 h at room temperature under Ar. The slightly pink colored solid that formed was
washed thoroughly with anhydrous diethyl ether until it became colorless. The solid product was
dried under the vacuum over P2O5 at room temperature. The sodium salt (2.37 g, 0.008 mol,
73%) was obtained as a colorless solid.
HRMS: m/z 571(48), 297 (MH+, 100), 275(49). IR υmax: 3409, 1595, 1443, 1243 cm-1. The
melting point of the salt was greater than 200 °C.
Attempts to Generate of Benzaldehyde-O-oxide in an O2 doped Argon Matrix
110
The light pink salt was placed into a stainless steel vial and was pumped on using the
matrix system overnight. In the experiment,
16
O2 (up to 20%) doped argon was flowed over the
salt as it was warmed to approximately 70° C. In the figure below, phenyldiazomethane was
assigned in the lower black trace spectrum. The heating element was removed and photolysis at λ
≥ 400 nm for 1 to 17 h resulted in the red trace spectrum. This was repeated several times with
the same results. It was concluded that the photolysis did not form the benzaldehyde-O-oxide but
instead the benzaldehyde-O-oxide may have rearranged into benzoic acid.
Reference: 1. Sander, W. J. Org. Chem. 1989, 54, 333.
111
A
9
8
7
6
5
4
3
2
1
-0
-1
4000
3500
3000
Name
Description
092711b Ar:16O2: C7H6N2 at 74degC
092711e Ar:16O2: C7H6N2 at 74degC irrad at 400nm and greater for 17 h
2500
cm-1
2000
1500
1000
500 400
112