Chm 222
Spring 2016, Exercise Set 2
Mass Spectroscopy
Infra Red and
1
H and 13 C NMR
Mr. Linck
c
Boniface
Beebe Productions
January 4, 2016
Version 4.1.
NOTE: An asterisk in the problem title indicates that it is a continuing problem from the
previous one. Two asterisk tells you the problem depends on the last two, etc.
2.1. Learning Organic Chemistry
Review your notes for the course to this point. Organize into major topics and sub-topics.
Your organization may not be chronological; in fact, it would probably be better if it was
not.
2.2. Review of Reaction Type
Identify the type of reaction (“addition”, “substitution”, or “elimination”) for the following:
(CH3 )2 CHCBr(CH3 )2 + (CH3 )3 CO− = (CH3 )2 CC(CH3 )2 + (CH3 )3 COH + Br−
What kind of compound is formed in this process? HINT: In an organic chemistry course
we focus on the “organic” molecule. In this case, that is the first one mentioned, not the
second, which merely serves as a base.
2.3. Mass Spectroscopy
We use mass spectroscopy only slightly in this course. The key to our usage involves the
molecular radical ion which is the molecule with one electron knocked out. It is an ion,
a cation to be precise, because of the loss of that electron. It is a radical because it has
an odd number of electrons. Since the mass of the electron is small compared to that of
nuclei, the mass of the molecular radical ion is essentially the same as that of the unionized
material from which it arose. Although modern spectrometers are capable of distinguishing
more finely, we shall stick with “integer” mass units: CH4 would have a peak at 16 mass
units. With that information, you should be able to handle problems such as this and the
following ones labeled “Mass Spectroscopy”: Octane would have a molecular ion peak at
what mass number?
2.13
2
2.4. Mass Spectroscopy
At what mass numbers would the M+. peaks be for the following compounds: C5 H10 O,
C5 H8 F2 , C3 H6 ?
2.5. Mass Spectroscopy
After the electron is removed, the molecular radical ion can also break into smaller fragments. The ions of these fragments are also detected in the mass spectrum. Hence we have
a number of peaks of mass of the molecular radical ion and peaks of smaller mass. In the
mass spectrum of a compound there are major peaks at 27, 39, 41, 55, 56, 69, and 84. If
the compound contains only C and H, what is the formula? HINT: Find the M+. peak and
use ihd.
2.6. Mass Spectroscopy and the Isoelectronic Relationship
Why do compounds with an odd number of nitrogen atoms have an odd mass number for
the molecular ion when the mass of N is 14. HINT: Think about typical groups that are
isovalent with the NH2 group.
2.7. Mass Spectroscopy
For Br, there are two common isotopes, 79 Br and 81 Br. These occur in nearly equal quantities in nature. These peaks are usually called the M+ and M+2 peaks, which is a nomenclature of convenience and does not mean that the second peak is dipositive. Work your way
through what the meaning is. What would the masses of the molecular ions be for ethyl
bromide and what are their relative intensities? HINT: Look carefully at the grammar of
the question, especially the (correct) use of plurality.
2.8. Mass Spectroscopy*
A compound has molecular ion peaks (judged to be so because there is nothing at a higher
mass number) of 136 and 138 of about equal intensity. Make an intelligent guess as to the
identity of the compound.
2.9. Mass Spectroscopy
A compound has “molecular” peaks in the mass spectrum at 135 and 137 of about equal intensity. What can you say about this compound? HINT: Think. There is more information
here than what first meets the eye; try to find it all.
2.10. Mass Spectroscopy
The common isotopes of Cl are 35 Cl and 37 Cl; the former is three times as abundant as the
latter. What would the masses of the “molecular ions” be for 3-chlorohexane and what are
their relative intensities? HINT: Again, the use of a plural.
2.11. Mass Spectroscopy and the M+1 Carbon Peak
There is an isotope of carbon, 13 C, which has an abundance of 1.1%. This means that for
every 1000 carbon atoms, you will find 11 atoms with the heavier isotope. If you had a
10000 molecules of CO2 , what is the chance that you would find one with a weight of 45?
2.12. Mass Spectroscopy and the M+1 Carbon Peak
If you had 100 molecules of C2 O4 H2 , what is the probability that you would find a molecule
of this substance with a mass of 91? HINT: A little trickier: 100 molecules contains 200
atoms of carbon.
Chm 222
Exercise Set 2
2.22
3
2.13. Mass Spectroscopy and the M+1 Carbon Peak
Compounds of carbon with lots of carbon atoms often show a small peak one unit in mass
higher than the molecular ion peak due to the 1.1% of carbon that is 13 C. If you have a
compound containing five carbons (each of which has a 1.1% chance of being a 13 C, what
will be the relative height of the M+1 peak relative to the M peak. HINT: Extrapolate
from the last two problems.
2.14. Mass Spectroscopy and the M+1 Carbon Peak
From the last several problems you should be able to deduce that the following formula
gives the number of carbon atoms in a compound, nC .
nC =
IM +1
IM
0.011
where IM and IM +1 are the intensities of the M and M+1 peaks, respectively. Do so.
2.15. Mass Spectroscopy
A compound has “molecular” peaks in the mass spectrum at (mass, (intensity)) 76 (25.3);
77 (0.9); 78 (8.0); and 79 (0.3). What can you say about this compound? HINT: This
course is trying to get you to put arguments together to arrive at a logical conclusion.
2.16. Mass Spectroscopy*
If you didn’t already obtain two facts about the compound in the last problem, do so now.
Use the M and M+1 peaks to estimate the number of carbon atoms or use the fact that
there is a M and an M+2 peak.
2.17. Scientific Consistency**
As a good scientist you should always make sure your data is consistent. In the last two
problems, you have established two things about the molecule. Are those things consistent
with the observed molecular mass?
2.18. M+1 Peak in Mass Spectroscopy
A substance of formula C8 H16 O has a molecular ion peak in the mass spectrum with intensity of 24.3. What would you expect for the intensity of the peak at M of 129?
2.19. Mass Spectroscopy
A compound has a mass spectrum with peaks at 186 and 188 of equal intensity, say 100,
and a peak at 189 of 7.8. What can you say about the compound?
2.20. Mass Spectroscopy*
The compound in the last problem has additional peaks in the mass spectrum: at 171 (51
units), 173 (52 units), and 174 (3.4 units). Can you say anything about what fragment was
lost from the original molecular ion?
2.21. Mass Spectroscopy
Here are some “fudged” data, manipulated to make your analysis easier. A compound has
mass spectrum peaks at 92 (intensity = 70.0) and 93 (5.5). How many carbons are in the
material?
Chm 222
Exercise Set 2
2.31
4
2.22. More Complicated Mass Spectroscopy*
Here is the real data for the compound in the last problem. The peaks and intensities near
the molecular ion peak are: 91 (100), 92 (77.7), and 93 (5.5). Figure out why and how I
“fudged” the data. Be sure you see that because I “fudged” the data in the last problem,
that problem was much easier than it might have been. HINT: Think about the number of
carbons likely in that peak at 91 and the consequences for the peak at 92.
2.23. Mass and IR Frequency
The frequency at which a peak occurs in the IR spectrum caused by a bond stretch is
governed by the equation:
s
1
k
ν=
2π µ
where k is the force
constant, a measure of the bond strength, and µ is the reduced mass,
m1 m2
equal to (m1 +m2 ) . Why do C-H, O-H, and N-H bond stretches occur at higher ν than
C-C, O-C, or N-C stretches?
2.24. Bond Strength and IR Frequency
Generally the C-H bond of an alkyne is stronger than that of an alkene, which is stronger
than that of a alkane. If the first of these absorbs near 3300 cm−1 , where would you expect
the others to absorb?
2.25. Bond Strength and IR Frequency
Why does a carbon-carbon double bonds stretch occur at higher ν than a carbon-carbon
single bond stretch?
2.26. Double versus Single Bonds in IR
Where would you expect double bonded carbon-oxygen (C=O) stretches to occur relative
to single bonded C-O stretches?
2.27. Triple versus Double Bonds in IR
Where would you expect the stretches of triple bonded carbon-carbon species to occur
relative to double bonded carbon-carbon molecules?
2.28. IR Frequencies
Where would you expect double bonded carbon-sulfur stretches to occur relative to double
bonded carbon-oxygen stretches? HINT: If there are multiple factors, and there are in this
question, then you should examine all of them.
2.29. Estimating IR Frequencies
The carbon-carbon stretch in alkynes typically occurs between 2100 and 2300 cm−1 . Approximately where would you expect nitriles, such as CH3 CH2 CH2 CN, butanenitrile, to
absorb?
2.30. Using IR to Identify Functional Groups
You have two compounds of formula C6 H12 . Compound A has peaks in the IR at 3016,
2861-2961, 1658 cm−1 and a bunch of stuff in the region below 1500 cm−1 . Compound B
has peaks at 2853-2928 cm−1 and a bunch of stuff below 1500 cm−1) . Which is cyclohexane?
Why do you reach this conclusion?
Chm 222
Exercise Set 2
2.40
5
2.31. IR and the Scientific Method
You are analyzing an IR and find a rather weak and narrow peak near 1675 cm−1 . Given
the weakness, should you ignore it or instantly check elsewhere in the spectrum? HINTS:
(1) Why would I ask if the answer wasn’t obvious? (2) Learn to “pursue” your analysis to
conclusions that are certain (First of many times this will be said.).
2.32. Coupling in IR
If the value of ν for a E-X stretch is close (in energy) to that for a E-Y stretch (where E
is some element and X and Y can be the same element), they often “couple” to give, for
instance, a symmetrical stretch (X and Y both moving away from the E at the same time)
and an asymmetrical stretch (X moving toward the E as Y moves away, and the reverse),
each with a slightly different ν. Compounds containing an -NH2 group have two peaks near
3300-3400 cm−1 . Why?
2.33. IR Interpretation*
The IR spectrum of dimethylmalonate, CH3 OC(O)CH2 C(O)OCH3 , has, not surprisingly,
a peak in the 1740 cm−1 region. Why? This peak is, however, considerably broader than
normal carbonyl peaks. Why is this so? Make an intelligent guess.
2.34. Learning the IR Positions
How many peak positions in the IR, between two elements, neither of which is a hydrogen
atom, are there? At what wave number is each? Is one slightly broader than the others?
Is one generally stronger than the others? Is one usually quite weak? HINT: I mean, of
course, peaks you should know about, those greater than 1500 cm−1 .
2.35. Learning the IR Positions
How many peak postions in the IR, between X-H, are there? Which are narrow and which
are broad? At what wave number is each? HINT: I mean, of course, peaks you should know
about.
2.36. Learning the IR Positions
How many peak postions in the IR should you know? At what wave number is each?
2.37. IR
What can you say about the following compounds given their IR spectra in the functional
group region (all reported in units of cm−1 ). A 3410 sharp, 2900-3000, 2150 sharp, but
weak; B 3400 broad, 2900-3020; C 2850-3000, 2710, 1725.
2.38. IR Peak Detail
Generally speaking, the broad O-H stretch in alcohols occurs near 3300 cm−1 and does not
interfere with the peaks due to C-H stretches, whereas the broad O-H stretch in carboxylic
acids usually occur at a lower wave number, nearer 3000 cm−1 and hence does overlap with
C-H stretches. This can be used to determine which of the two kinds of O-H group is
present. A compound of the formula C9 H18 O2 absorbs with a broad peak near 3020 cm−1 .
What might the compound be?
2.39. Review of Carbon Level
What carbon level is the carbon atom in CH2 O? What carbon level is the carbon atom in
CH3 OH?
Chm 222
Exercise Set 2
2.49
6
2.40. Review of a Reaction
What is the product when CH2 O is treated with 1) BH–4 followed by 2) H+ ?
2.41. Changing Carbon Level*
In the last problem the carbon level changed from 2 to 1 upon treatment with an H–
equivalent followed by H+ . We could say that the carbon level was reduced by H– and H+ ,
which is electronically equivalent to H2 . What reagent lowers the carbon level? HINT:
There is a specific answer, rather obvious, and a generic one, involving oxidation states,
only slightly less obvious.
2.42. Changing Carbon Level
Write a balanced reaction for the lowering of the carbon level of CH2 O by one unit with
H2 .
2.43. Changing Carbon Level
Write a balanced reaction for the raising of the carbon level of CH3 OH by one unit with
O2 (half a mole).
2.44. Raising Carbon Level and Electron Acceptors
Oxygen molecules are good electron acceptors. Why?
2.45. Raising Carbon Level and Electron Acceptors
Generally speaking, species that want to gain electrons are likely to be able to raise the
carbon level of an organic molecule. Which of the following would you expect to be a good
electron acceptor (or speaking professionally, a good oxidant): F– , F2 , H2 O, O3 , Cr2+ ,
–
CrO2–
4 (a Cr(VI) compound), MnO4 (a Mn(VII) compound)?
2.46. Carbon Levels
What is the carbon level of the interesting carbon in 3-hexanol, C6 H14 O? of 3-hexanone,
C6 H12 O?
2.47. Reaction and IR
A student treats 3-hexanol with PCC (a Cr(VI) compound officially called pyridinium
chlorochromate, C5 H5 NH+ CrClO–3 , which we will use extensively later in the semester; it
is a good oxidizing agent) to try to form 3-hexanone. What should she look for in the IR
to verify that reaction occurred? HINT: Remember a good scientist looks for confirmation
of observations.
2.48. Reaction
What is happening in the following reaction? HINTS: (1) An answer in several different
manners would be nice: carbon level; oxidation/reduction; kinds of compounds destroyed,
formed. (2) Unless you are sure what you are seeing, write out the reaction in our normal
line (zig-zag) form.
CH3 CH(OH)CH2 CH2 CH3
Chm 222
P CC
−−−→
CH3 C(O)CH2 CH2 CH3
Exercise Set 2
2.57
7
2.49. Synthesis
How would you prepare propanone, CH3 C(O)CH3 , from 2-propanol, CH3 CH(OH)CH3 ?
HINTS: (1) The procedure is to ask 1. “What kind of compound is the one that I desire to
make?”, and then 2. “What ways do I know to make that kind of compound?” (2) Then, if
you haven’t figured out the answer, you might ask, “Is there any method that I just learned
that maybe this question is reviewing?”
2.50. Changing Carbon Level
What is happening in this reaction? HINTS: (1) An answer in several different manners
would be nice: carbon level; oxidation/reduction; kinds of compounds destroyed, formed.
(2) Unless you are sure what you are seeing, write out the reaction in our normal line
(zig-zag) form.
CH3 C(O)CH3
1.BH−
4
−−−−→
2.H+
CH3 CH(OH)CH3
HINT: The notation 1. blah blah, 2. yap yap means add the first reagent, wait for reaction,
then add the second.
2.51. Changing Carbon Level
What is happening in this reaction? HINTS: (1) An answer in several different manners
would be nice: carbon level; oxidation/reduction; kinds of compounds destroyed, formed.
(2) Unless you are sure what you are seeing, write out the reaction in our normal line
(zig-zag) form.
CH3 C(O)CH3
1.CH MgI
−−−−3−−→
2.H+
(CH3 )3 COH
2.52. Review of Synthetic Reactions
How do you oxidize a carbon level 1 compound to carbon level 2 compound? How do you
reduce a carbon level 2 compound to a carbon level 1 compound?
2.53. Review of Synthetic Reactions*
There are two kinds of answers to the second question in the last problem. How do they
differ?
2.54. Synthetic Reactions
Let’s go up a notch. At this point in the course, speaking in general terms, how would you
prepare a ketone (what carbon level?) from an alcohol (what carbon level?) with fewer
carbon atoms? HINTS: (1) Learn to think your way through problems of this sort if you
want to be successful in organic chemistry. The only way we know to make C-C bonds
(at the moment) is to react a ketone or aldehyde with a “C− ” reagent, so that must be
there somewhere. (2) Use problem 47 and, when you finish, congratulate yourself for this
synthesis containing multiple steps.
2.55. Synthetic Reactions
How would you prepare 2-butanol from ethanal and ethyl bromide? HINT: Go backwards
(officially called retrosynthetic analysis): “How do I make an alcohol?”
Chm 222
Exercise Set 2
2.64
8
2.56. Reactions
How would you prepare 2-butanone from ethanal and ethyl bromide? HINTS: (1) Go
backwards. (2) Think about the last problem and remember something from problem 47.
2.57. Reactivity and IR
A sample of propanone is treated with CH3 MgCl and then H+ in water. What would be
the product of the reaction? How would you detect that reaction occurred using IR?
2.58. Functional Groups from IR
What can you say about the compound whose IR is given in Figure 1?
2.59. An Oxidizing Agent
Ozone, O3 , is a powerful oxidizing agent. Draw a Lewis structure of ozone and determine
why it wants electrons so badly.
2.60. Oxidizing Agents and Carbon Level
Given that ozone, O3 , is a powerful oxidizing agent (see the last problem), should it be
capable of taking a carbon level 1 compound to carbon level 2?
2.61. Carbon Level
An alkene reacts with H2 to produce an alkane,
CH3 CHCH2
catalyst
+ H2 −−−−−→ CH3 CH2 CH3
Let’s apply some logic. (1) What is the carbon level of the carbon atoms in the product?
(2) Given that problem 41 shows that H2 is a reductant that lowers carbon levels by one
unit, what must be the carbon level of one of the carbons in the reactants? (3) The affected
carbons in CH3 CHCH2 must be the last two, as the first is certainly not attached to anything
funny. Conclusion: Could we say that an alkene is a delocalized carbon level 1 (or, if you
like, each carbon with a double bond to another carbon is carbon level 1/2)? What would
be the carbon levels in CH3 CH3 CHCHCH3 ? or you might just answer the question for the
interesting carbon atoms.
2.62. Oxidizing Agents and Carbon Level*
Continuing with the logic of the last problem: If an alkene is a delocalized carbon level
1 compound, and ozone is an oxidizing agent, what carbon level might the products of a
reaction between an alkene and ozone have? HINT: There are multiple answers to this
problem. Take the smallest change.
2.63. Ozonolysis of an Alkene**
A molecule of 2-pentene reacts with O3 followed by treatment with Zn to form a mole of
ethanal and a mole of propanal (as we will examine more carefully later). This may be the
only reaction we will learn this semester that cleaves a carbon-carbon bond, and a double
bond at that! Write out a summary of this reaction (from the point of view of the carbon
skeletons–the stoichiometry of the process is not simple) and see if you can figure out how
to predict what happens when ozone reacts with an alkene and the product is then treated
with Zn. HINT: Look hard at what you did to solve this problem. I am giving it here in
the hope that it will ease your life later on, but that hope depends on your diligence.
Chm 222
Exercise Set 2
2.64
9
Figure 1: IR for Problem 58
Chm 222
Exercise Set 2
2.76
10
2.64. Reactivity and IR***
What would you look for in the IR to determine if the reaction in the last problem occurred?
2.65. Ozonolysis and IR
Predict the product of the reaction of ozone, O3 , with 2-hexene followed by treatment with
Zn. What would you look for in the IR to identify the nature of the products?
2.66. Prediction of Ozonolysis Products
Extrapolate your knowledge by predicting the product of the reaction of ozone, O3 , with
2-methyl-2-butene, followed by Zn. HINT: An H and a CH3 group are isovalent.
2.67. Reactivity and Hydrogenation
As we saw above, H2 reduces carbon level. The compound 2-butene reacts with H2 in
the presence of Pd metal coated with charcoal (written Pd(C)) to yield butane (as we will
examine more carefully later). This is one of the few ways we will learn this semester that
removes a functional group from a molecule. Write out the stoichiometry of this process.
How would you classify the reaction, “addition, elimination, or substitution”? HINT: Here
again we have a future reaction that you might try to get used to using.
2.68. Reactivity and IR
For the reaction in the last problem, what would you look for in the IR to detect the
occurrence of the reaction?
2.69. Reactivity
What product would you predict if you reacted H2 and Pd(C) with 2-methyl-2-butene?
2.70. Reactivity and IR
What product would you predict if you reacted H2 and Pd(C) with 1,3-pentadiene? What
IR signal could you follow to determine the extent of this reaction?
2.71. Review of Three Reactions
In the past tens of problems we have looked at three reactions. What are they?
2.72. Review of Three Reactions
What reaction would you use to convert an alcohol into a ketone or aldehyde?
2.73. Review of Three Reactions
What reaction would you use to convert an alkene into an alkane?
2.74. Review of Three Reactions
What reaction would you use to convert an alkene into two carbonyl compounds?
2.75. IR Identification of Functional Groups
What can you say about the compound whose IR has, in addition to the normal peaks, a
broad peak at 3100 cm−1 and a intense, slightly broadened, peak near 1720 cm−1 .
Chm 222
Exercise Set 2
2.87
11
2.76. IR
What can you say about the following compounds given their IR spectra in the functional
group region (all reported in units of cm−1 ). A 3450-3600, broad with some sharp peaks on
top of it in the 2950-3000 region, 1723 intense; B 3450-3600, broad with some sharp peaks
on top of it in the 2950-3000 region, 1700 intense, 1650 sharp; C broad peak centered at
3350, 3080 sharp,1650, sharp.
2.77. IR Frequency
If I told you that a carbon-fluorine bond stretch occurred at about 1050 cm−1 , what would
you predict for the frequency of a carbon-chlorine bond stretch?
2.78. IR Frequency*
If I then told you (in addition to what I said in the last problem) that the bond strength
of the carbon-fluorine bond is about 25 kcal/mole stronger than the corresponding carbonchlorine bond, how would your answer to the last problem be changed?
2.79. IR
Figures 2 and 3 give two IR spectra, both of compounds of the formula C5 H10 O. Find a
structure that is consistent with each spectrum.
2.80. Review of Epwa and Reactivity
Use epwa to show what happens when BH–4 reacts with 2-pentanone.
2.81. Review of Epwa and Reactivity
Use epwa to show what happens when the product of the last problem reacts with dilute
H3 O+ , also called H+ .
2.82. Epwa and Reactivity
Use epwa to show what happens when OH– reacts with 2-propanone.
2.83. Classification of Reactions
How do you classify the net reaction in problems 80 followed by 81? How do you classify
the reaction in problem 82?
2.84. Stability of Negatively Charged Species
Consider H− and OH– . Which compound would you guess is more tolerant of the negative
charge? HINT: Periodicity.
2.85. Reversibility of Reactions
If I told you that the reaction in problem 80 was irreversible and that in reaction 82 was
reversible, how would you explain it? HINT: Note in both cases the carbon species is the
same; what differs is the “leaving group” in the second case. Getting this concept now will
make the rest of the course much easier.
2.86. IR and Reactivity
Propanal, whose IR spectrum has an interesting peak at 1740 cm−1 reacts with a reagent
to produce a compound whose spectrum no longer has the 1740 cm−1 peak, but now has an
interesting peak at 3350 cm−1 ; this peak is broad and strong. What can you say happened
in the reaction? HINT: By “interesting” I mean within the context of this problem.
Chm 222
Exercise Set 2
2.87
12
Figure 2: IR for Problem 79
Chm 222
Exercise Set 2
2.87
13
Figure 3: IR for Problem 79
Chm 222
Exercise Set 2
2.99
14
2.87. Another Summary of IR: X-H Stretches
Make a summary of the position, intensity, and broadness of peaks caused by various X-H
stretches in the region between 2700 and 3600 cm−1 .
2.88. Another Summary of IR: Double Bond Region
Make a summary of the position, intensity, and broadness of peaks caused by various
stretches in the region between 1500 and 1800 cm−1 . HINT: I am looking for only two
entries in your list.
2.89. IR and Frequency
The force constants for the C-H bond and the C-C bond are about the same. Yet the C-H
bond stretch occurs at a much higher wave number than does the C-C stretch, which is
buried in the “garbage” below 1500 cm−1 . Why?
2.90. ihd Review
What is ihd? What does it tell you?
2.91. IR Identification
Two isomers of C4 H6 O, A and B, are both symmetric. Isomer A has IR peaks at 3090
and 1620 cm−1 , whereas isomer B has peaks at <3000 and 1780 cm−1 . Neither material
absorbs in the 3300-3700 cm−1 region. Propose structures for the two isomers.
2.92. Use of IR
You would (if you are wise) never use IR to tell the difference between a compound containing a C-Cl bond and one containing a C-Br bond. Why not?
2.93. IR and Frequency
If you were pressed on the issue posed in the last problem, what would you say the difference
between the two would be?
2.94. IR of Carbonyls
Without looking at any tables or books, at roughly what energy (units of wave number) do
carbonyl compounds absorb in the IR?
2.95. IR of Alcohols
Without looking at any tables or books, at roughly what energy (units of wave number) do
alcohols compounds absorb in the IR?
2.96. IR of Alkenes and Learning Organic Chemistry
Without looking at any tables or books, at roughly what energy (units of wave number)
do alkene compounds absorb in the IR? HINT: If you can’t answer the last three questions
you are not studying correctly in this course.
2.97. Use of IR
Are 2-butanone and but-2-en-1-ol isomeric? Do they have the same ihd? How could you
use IR to distinguish between 2-butanone and but-2-en-1-ol?
2.98. IR Intensities
Why is the C triple bond C stretch absent in the IR of a symmetrical alkyne?
Chm 222
Exercise Set 2
2.108
15
2.99. IR Intensities
Why is the C triple bond C stretch weak in the IR of an asymmetrical alkyne?
2.100. IR Intensities
Why is the stretch of a double bonded C=O of high intensity whereas that of a normal
double bonded C=C considerably less intense?
2.101. IR
How would you distinguish between compounds 1 and 2 using IR?
2.102. IR of Unknowns
Here are three IR spectra, A, B, and C. Spectrum A: <3000 including 2700; 1722 cm−1 ;
Spectrum B: Broad peak with two maxima 3200-3400, <3000, broad peak 1620-1680 cm−1 ;
Spectrum C: 3110, <3000, 1645 cm−1 . Assign each spectrum to one of the compounds 3-7.
2.103. Review of Reactions
What would be the product of the reaction of 2-hexene with H2 over Pd(C)?
2.104. IR*
How could you use IR to tell when the reaction between 2-hexene and H2 /Pd(C) was
complete?
2.105. Review of Reactions
What would be the product of the reaction of 2-hexene with O3 , followed by Zn?
2.106. IR*
How could you use IR to tell when the reaction between 2-hexene and O3 , followed by Zn,
was complete?
2.107. Review of Reactions
What would be the product of the reaction of 2-hexanone with BH–4 , followed by H+ ?
Chm 222
Exercise Set 2
2.114
16
Table 1: Chemical Shifts of Methine, Methylene, and Methyl Groups, in δ.
XRCH2 FClClCH2 HORCCC6 H5 ORC(O)-
X-CH-R2
1.5
4.8
4.05
1.95
3.95
2.8
4.5
2.65
X-CH2 -R
1.2
4.45
3.45
1.80
3.55
2.2
4.05
2.3
X-CH3
0.9
4.25
3.05
1.50
3.2
1.7
3.85
2.1
2.108. IR*
How could you use IR to tell when the reaction between 2-hexanone and BH–4 , followed by
H+ , was complete?
2.109. Review of Reactions
What would be the product of the reaction of 2-hexanone with CH3 MgI, followed by H+ ?
2.110. IR*
How could you use IR to tell when the reaction between 2-hexanone and CH3 MgI, followed
by H+ , was complete?
2.111. IR and Mass Spectroscopy
A molecule is isolated from a biological sample. It has the following IR: a broad peak
between 3200 and 3600 cm−1 and two peaks in the region between 1600 and 1700 cm−1 .
What functional groups are in the molecule? The mass spectrum shows a M+1 peak with
relative intensity of 3.9 and a M peak of intensity 27.2. How many carbons are (likely) in
the molecule?
Here we begin our analysis of NMR structure determination.
2.112. The Basis of NMR Shift
All bare protons in a magnetic field of fixed strength have a transition between the two spin
states (up and down) at the same energy. Why do hydrogen atoms in different environments
in molecules have signals at different energies?
2.113. NMR-Chemical Shift
Table 1 gives the chemical shift (in units of δ) of compounds with methyl, methylene (-CCH2 ), and methine (C2 CH-) hydrogen atoms. For instance, the signal due to the methylene
protons in CH3 CH2 OH would occur at approximately 3.55 δ. What do you learn about the
relative chemical shift of methine versus methylene versus methyl hydrogen atoms when the
X group on the carbon is the same?
Chm 222
Exercise Set 2
2.122
17
Table 2: Chemical Shifts of Various Fragments
Fragment
alkene-CH3
alkene-H
alkynyl-H
R−NH2
RCH2 O−H
δ
1.7
4.5-6.0
2.5
1.5-4.0
2-5
Fragment
C6 H5 -H
C6 H5 −CH3
C(−O)−H
RC(O)O−H
C6 H5 O−H
δ
6.5-8.0
2.3
9.0-10.0
10-12
4-7
2.114. NMR-Chemical Shift
What do you learn about the position of a CH3 C(O)R signal? HINT: When I see a δ 2.1
signal I hear “ding, (pause), ding, (pause) ding” and I burst into song: “It’s three o’clock
in the morning, we’ve danced the whole night thru . . . ” written by Theodora Morse (as
Dorothy Terriss) and Julian Robledo in 1921.
2.115. NMR-Chemical Shift
From Table 1, what do you learn about a CH3 -C signal compared to a CH3 -O signal? HINT:
The professional would use words like “down field” or “up field.”
2.116. NMR-Chemical Shift
From Table 1, what do you learn about a -CH2 R signal compared to a -CH2 -Cl signal?
HINT: R is some unspecified collection of C and H atoms, which is “innocent.”
2.117. NMR-Chemical Shift
From Table 1, what do you learn about the methyl group signal in CH3 CH2 Cl compared to
the methyl group signal in CH3 Cl? What would you predict for the methyl group signal in
CH3 CH2 CH2 Cl?
2.118. Learning Organic Chemistry
Summarize in a concise manner what you learn from a careful study of Table 1.
2.119. NMR-Chemical Shift
Table 2 lists the chemical shift of some hydrogen atoms in compounds that you should
know. NOTE: All data are approximate and will vary from molecule to molecule. Similar
data is also available on the chemistry department web page under “Resources”. If you had
a compound with a signal near 5 δ, what structural feature would you suspect was in your
molecule?
2.120. Learning How to Verify*
Would there be any information that would aid you in your answer to the last question?
What would that information be?
2.121. NMR-Chemical Shift
True or false? If I told you that there is a signal in the 1 H nmr at 4.0 δ, you would be
justified in saying “This molecule contains an ROH group.” Give your reasoning.
Chm 222
Exercise Set 2
2.128
18
Table 3: Electronegativity and Chemical Shifts
E
F
Cl
Br
I
OH
NH2
SiH3
BeCH3
χ
4.0
3.2
3.0
2.7
3.4
3.0
1.9
1.6
δ
4.3
3.0
2.7
2.2
3.4
2.36
0.04
-1.0
2.122. NMR-Chemical Shift
Which of the following hydrogen nuclei would you expect to have a signal at higher field
(near TMS, that is, (CH3 )4 Si), lower δ, and which at lower field (near CHCl3 ), higher δ?
a. R2 BCH3 , b. CH2 F2 , c. CCl3 CHClCCl3 , d. N(CH3 )+
4 . HINTS: (1) “R” is just some
unspecified collection of carbon and hydrogen atoms. (2) Be careful with the last compound;
think about what causes chemical shifts.
2.123. The Fickle -OH and Learning Organic Chemistry
Boniface Beebe, the highly admired natural philosopher of Searcy, Arkansas, wrote: “I have
an proton with a signal at about δ 4.0. There must be an ‘H of an OH’ in my sample.”
What would you say to Bonnie?
2.124. NMR-Chemical Shift
Which member of each pair would you expect to have the most downfield signal? a. CH3 Cl
or C2 H6 ; b. CCl3 CH3 or CF3 CH3 ; c. CH3 R or CH2 ClR; d. RC(O)CH3 or RCH3 . HINT:
R is, as usual, a non-electronegative/non-electropositive group typically containing C and
H atoms.
2.125. NMR-Chemical Shift
What is the chemical shift of a -CH3 group next to a benzene ring? Given that, make a
rough prediction for the position of the signal from a -CH2 group attached to a benzene
ring. How about a -CH group? What method did you use to come to your conclusions?
HINT: This kind of reasoning is critical. Think about what you need to do to get yourself
to be able to produce it.
2.126. NMR-Chemical Shift
Might a -CH2 group between a benzene ring and a -CH2 Cl group appear deshielded? Why?
2.127. NMR-Chemical Shift
Table 3 contains some data on the chemical shift of the -CH3 group for compounds of the
type CH3 E where E is given in the table and χ is the electronegativity of the atom of E
attached to the carbon. Do you see any relationships? HINT: Whenever a scientist is asked
that kind of question, she makes a plot, even if it is only crude.
Chm 222
Exercise Set 2
2.135
19
2.128. NMR Environments
How many different environments do the hydrogen atoms have in each of the following?
a. 1-chloropropane; b. 2-chloropropane; c. 2,3-dimethylbutane; d. 2,2-dichloropropane.
HINT: Make sure that you consider free rotation.
2.129. NMR Environments
Are all the hydrogen atoms in the same environment in 10? in 11? in 12? in 13?
2.130. NMR Environments
How many different environments are there in the compounds of the last problem that don’t
have only one environment?
2.131. NMR Environments
How many 1 H nmr signals will we see for each of the compounds 14-17? HINT: If you have
heard of it, ignore spin-spin coupling.
2.132. NMR Environments
The 1 H nmr spectrum of toluene shows a sharp peak at 2.28 δ and a broader peak at 7.1 δ.
How many different peaks should be present in toluene (which is the trivial name for methylbenzene)? Account for the observed spectrum. HINT: You might use the words “accidentally equivalent” in your answer.
2.133. Learning Organic Chemistry
Actively review your notes from the last lecture; don’t just read them. Summarize the
points of discussion. Close your notes and repeat to yourself the summary. How are the
points of discussion interconnected? Would you have connected them in the same way?
2.134. NMR and Chemical Shift
Predict the approximate position of the signal(s) in the 1 H nmr spectrum for 2-butenal and
for methylbutyrate. HINT: Ignore spin-coupling.
Chm 222
Exercise Set 2
2.143
20
2.135. NMR, Chemical Shift, and Integration
Predict the approximate position of the signal(s) in the 1 H nmr spectrum for 2-methyl-2propanol, 1-chloro-2,2-dimethylpropane, propene, and ethylchloride. It isn’t necessary, but
if you want to be reasonably accurate use the nice tables at
http://www.chem.wisc.edu/areas/reich/handouts/nmr-h/hdata.htm
.
Give integrations. HINT: You should neglect spin-spin coupling in this problem.
2.136. NMR, Chemical Shift, and Integration
Predict the approximate position of the signal(s) in the 1 H nmr spectrum for compounds
18-20. Give integrations. HINTS: (1) You may treat all of the hydrogen atoms in a benzene
rings as equivalent for now. (2) You should neglect spin-spin coupling in this problem.
2.137. NMR, Chemical Shift, and Integration
How would you distinguish between 21 and 22 using 1 H nmr (ignoring spin-spin coupling)?
2.138. NMR, Chemical Shift, and Integration
How would you, in principle, distinguish between 23 and 24 using 1 H nmr (ignoring spinspin coupling)?
2.139. NMR, Chemical Shift, and Integration
How would you distinguish between 25 and 26 using 1 H nmr (ignoring spin-spin coupling)?
2.140. NMR, Chemical Shift, and Integration
Predict the approximate positions of the signals and their relative areas in the 1 H nmr
spectrum of CH3 C(O)OCH3 .
2.141. NMR, Chemical Shift, and Integration
Predict the approximate positions of the signals and their relative areas in the 1 H nmr
spectrum of 2-bromobutane.
2.142. NMR, Chemical Shift, and Integration
A compound of formula C2 H6 O has only one peak in the nmr spectrum. Give a structural
formula for this compound? HINT: Use ihd.
Chm 222
Exercise Set 2
2.154
21
2.143. NMR, Chemical Shift, and Integration
A compound of formula C3 H6 Cl2 has only one peak in the nmr spectrum. Give a structural
formula for this compound?
2.144. NMR, Chemical Shift, and Integration
Find the number of 1 H signals, predict their positions, and state their relative areas for
compounds 27-30. HINT: Treat all protons on the benzene ring as if they were “accidentally
degenerate.”
2.145. NMR, Chemical Shift, and Integration
How many different chemical shifts would you expect in 1-chloro-3-fluoro-propane? Which
signal is due to which hydrogen atoms? What are the relative areas? Ignore spin-coupling.
2.146. NMR, Chemical Shift, and Integration
A compound of formula C4 H9 Br has three 1 H nmr signals, one at about 1.0 δ (Area 3),
a second at 2.0 δ (0.5) and a third at 3.3 δ (1). What is the compound? HINTS: (1) If
you have heard of spin-spin splitting, ignore it for this problem. (2) As always, if given a
formula, use ihd.
2.147. NMR Areas*
In the last problem, articulate how you handled the relative areas given the total number
of hydrogen atoms in the molecule was 9.
2.148. NMR, Chemical Shift, and Integration
A compound with the formula C7 H14 O has two 1 H nmr signals. What is the compound?
HINT: If you have heard of spin-spin coupling, ignore it.
2.149. NMR Complexity*
In the last problem, articulate what you can conclude from the relative simplicity of the
nmr spectrum and the complicated formula–14 hydrogen atoms.
2.150. NMR, Chemical Shift, and Integration
A compound with the formula C5 H12 O has 1 H nmr signals at 3.2 δ (20) and 1.2 δ (59).
What is the compound?
2.151. NMR Areas*
In the last problem, articulate how you handled area ratios that looked to be 6 to 2 when
you had a total of not 8, but 12 protons.
2.152. NMR, Chemical Shift, and Integration
A compound with the formula C9 H10 O2 has 1 H nmr signals at 7.4 δ (108), 5.2 δ (45) and
2.2 δ (66). What is the compound? HINTS: (1) Last time: As always when given a formula,
use ihd. (2) Ignore spin-spin coupling and treat all protons on a benzene ring as if they are
in one environment.
2.153. NMR and Reactions
How many 1 H nmr signals will the product of the reaction of 3-pentanone with ethylmagnesium Grignard have (after acidification) in the 1 H nmr spectrum? HINT: Ignore spin-spin
coupling.
Chm 222
Exercise Set 2
2.161
22
2.154. NMR and Reactions
How many 1 H nmr signals will the product of the reaction of trans-2-butene with ozone,
O3 , followed by treatment with Zn, have in the 1 H nmr spectrum? What will be their
approximate positions? Ignore spin-spin coupling.
2.155. NMR and Reactions
How many 1 H nmr signals will the product of the reaction of trans-2-butene with H2 over
Pd(C) have in the 1 H nmr spectrum? What will be their approximate positions? Ignore
spin-spin coupliing.
2.156. NMR, Chemical Shift, and Integration
Bromomethyl-methyl ether has an 1 H nmr spectrum with signals at 5.7 δ (2) and 3.2 δ (3).
Assign the peaks to hydrogen atoms in the structure.
2.157. NMR Analysis*
Look at your assignment in the last problem and think about it. Do this regularly with all
nmr structures. It will serve you well in the future to have a good grasp on where signals
occur. Oops, forgot to ask a question; this must be important.
2.158. NMR, Chemical Shift, and Integration
1-Bromo-2-methylpropane has an 1 H nmr spectrum with signals (ignoring spin-spin coupling) at 1.05 δ (6), 1.98 δ (1) and 3.3 δ (2). Assign the peaks to hydrogen atoms in the
structure; then see the last problem.
2.159. NMR, Chemical Shift, and Integration
A compound of formula C7 H14 O has the following 1 H nmr spectrum (with integration): 1.0
δ (Area 18) 2.1 δ (6), and 2.3 δ (4). What is the compound?
2.160. NMR Analysis*
Look at your assignment in the last problem and look how beautifully the data in Table 1
allow you to easily solve it. Note that 0.2 δ difference (observed in the problem) between
the methylene group and the methyl group is exactly what it is in the table. Do you think
Table 1 is useful?
Chm 222
Exercise Set 2
2.172
23
2.161. NMR, Chemical Shift, and Integration
A compound of formula C9 H13 N has the following 1 H nmr spectrum (with integration): 2.25
δ (3) 3.4 δ (1), and 7.3 δ (2.5). What is the compound? Be sure that you can account for the
values of the various chemical shifts. HINT: You may need those “accidentally equivalent”
words again.
2.162. NMR Analysis*
Look at your assignment in the last problem. Why are the methylene protons deshielded?
2.163. NMR and Chemical Shift
Predict the approximate positions of the signals present in the 1 H nmr spectrum of CH3 C(O)CH3 .
HINT: Hear any bells?
2.164. NMR, Chemical Shift, and Integration
How would you use chemical shift and integration to distinguish between HCCCH2 OH and
H2 C−CHC(O)H? HINT: Make sure you have the Lewis structures before you answer.
2.165. NMR, Chemical Shift, and Integration
A compound with the formula C6 H3 Cl2 (NO2 ) has an 1 H nmr spectrum (with integration):
7.63 δ (1) 8.09 δ (1), and 8.36 δ (1). What structures are not possible? HINTS: This
compound has a benzene ring; and the signals in that ring are not accidentally degenerate.
(2) The problem ignores spin-spin coupling. (3) The formula implies that the compound
contains an -NO2 group (isovalent with H) and not some other combination of N and O.
2.166. NMR and Equivalent Protons
How many 1 H nmr signals in 31-33? HINTS: (1) If you think about the ring as being planar
(it isn’t, but that works, as we will see), and consider hybridization for four- coordinate
carbons, you will find the first two molecules have a top and a bottom side. (2) This makes
the first two problems somewhat challenging.
2.167. NMR, Chemical Shift, and Integration
Using chemical shift and integration data only, how would you distinguish between 34 and
35?
2.168. NMR and Chemical Shift
In 1 H nmr, where does the H atom in RC(O)OH absorb? HINT: “R” is some unspecified
C,H group. HINT: There are two odd ball chemical shifts in 1 H nmr; this is one of them.
2.169. NMR and Chemical Shift
In 1 H nmr, where does the H atom in CH3 C(O)R absorb?
2.170. NMR and Chemical Shift
In 1 H nmr, where does the H atom on an alkene absorb?
2.171. NMR and Chemical Shift
In 1 H nmr, where do the H atoms in benzene-R absorb?
Chm 222
Exercise Set 2
2.183
24
2.172. NMR and Chemical Shift*
In 1 H nmr, where does the H atom in CF3 C(O)H absorb? As they say in Beebe, Arkansas,
which is right down the road from Searcy, “There ain’t no more bells in 1 H spectroscopy,”
than those you have discussed in this and the previous four problems.
2.173. NMR and Spin-Spin Splitting
A -CH3 group has a neighboring C with one H atom. How many different spin orientations
can that single neighboring hydrogen atom take?
2.174. NMR and Spin-Spin Splitting*
Given your answer to the last problem, how many different magnetic fields can the -CH3
group that has one H atom on a neighboring carbon “see?” Into what kind of structure is
the signal of the -CH3 group split?
2.175. NMR and Spin-Spin Splitting
A -CH2 - group has one H atom on a neighboring carbon atom. How is the -CH2 - group
split?
2.176. NMR and Spin-Spin Splitting
Complete the following sentence: “To determine the splitting of the hydrogens on a given
carbon, you need to examine the . . . ”
2.177. NMR and Spin-Spin Splitting
A -CH3 group has two equivalent H atoms on a neighboring carbon atom. How many
different spin orientations can those two neighboring hydrogen have? List them pictorially.
What is the relative probability of each of the possible orientations? Do any of the possible
orientations produce equivalent fields? How many different fields are possible? What is the
probability of each?
2.178. NMR and Spin-Spin Splitting*
A -CH3 group has two equivalent H atoms on a neighboring carbon atom. How will the
signal of the -CH3 group be split? What will be the relative areas of the components of the
signal?
2.179. NMR and Spin-Spin Splitting
A -CH2 - group has three equivalent H atoms on a neighboring carbon atom. How is the
-CH2 - group split?
2.180. NMR and Spin-Spin Splitting
A -CH= group has two neighboring equivalent -CH3 groups. How is the CH group split?
2.181. NMR and a Spin-Spin Splitting Rule
From the last eight problems, show that the number of peaks into which a signal is split is
given by the expression (n+1), where n is the number of neighboring hydrogen atoms.
2.182. NMR and Splitting Pattern
Predict the spin splitting of the peak due to the hydrogen atom on the methyl group of
CH3 CH(Cl)2 .
Chm 222
Exercise Set 2
2.193
25
2.183. NMR and Splitting Pattern
Predict the spin splitting of the peak due to the hydrogen atom on the methine group of
CH3 CH(Cl)2 .
2.184. NMR and Splitting Pattern
Predict the spin splitting of the peak due to the hydrogen atom on the methyl group of
CH3 CH2 OH.
2.185. NMR and Splitting Pattern
Predict the spin splitting of the peak due to the hydrogen atom on the methylene group
of CH3 CH2 OH. HINT: Ignore the hydrogen atom on the oxygen atom: Under normal
circumstances, rapid exchange wipes out any spin-spin coupling of this hydrogen atom.
2.186. NMR and Splitting Pattern
Predict the spin splitting of the peak due to the hydrogen atom on C-2 of 34.
2.187. NMR and Splitting Pattern
Predict the spin splitting of the hydrogen atoms of 36.
2.188. NMR and Splitting Pattern
Predict the spin splitting of the peak due to the hydrogen atom on the methyl group of 35.
2.189. NMR and Splitting Pattern
Here is a slightly harder spin-spin coupling problem. Predict the spin splitting of the peak
due to the hydrogen atom on C-2 of 35. Be careful; the fluorine atom has a spin of 1/2 but
clearly is not equivalent to a hydrogen atom.
2.190. NMR Splitting Pattern
Predict the spin-spin splitting pattern (i.e., triplet at 1.5 δ, etc) for 1,1,2-tribromoethane.
2.191. Reciprocity of NMR Splitting Pattern
Imagine you have a -CH3 group next to a -CH2 - group. From the point of view of the
-CH3 group, how many neighbors does it have? What splitting will you see at the -CH3
group? From the point of view of the -CH2 - group, how many neighbors does it have? What
splitting will you see at the -CH2 - group? Since the two interactions are modulated by the
same electrons, they are completely reciprocal. If the -CH2 - group “splits” the -CH3 group,
the -CH3 group will “split” the -CH2 - group. How will each be split?
2.192. Reciprocity of NMR Splitting Pattern*
Continuing with the scenario from the last problem, the magnitude of the splitting, almost
always called J, is eactly the same at both signals. If the -CH3 group is split into a triplet
with a separation between the peaks of J = 8.0 cps, what will be the separation of the
various peaks in the -CH2 - group?
Chm 222
Exercise Set 2
2.199
26
2.193. NMR
A compound of formula C4 H8 O has three 1 H nmr signals: 1.06 δ (triplet J=7.6, 3), (ding)
2.14 δ (s, 3) (ding), and 2.45 δ (q, J=7.6, 2). What is the compound?
2.194. NMR and Learning Organic Chemistry
When you work on nmr problems, figure out something that you know and then pursue it.
For instance, in the problem, “A compound of formula C4 H8 Br2 has two 1 H nmr signals:
1.97 δ (s, 6) and 3.89 δ (s, 2). What is the compound?” I could start with the signal at 3.89
δ which is deshielded and hence must be next to one bromine atom and probably adjacent
to another. Now to pursue: That same signal is a singlet so there is no hydrogen close to
the hydrogen(s) in the signal. We have:
where the squiggly lines are NOT to hydrogens, and one of them is probably to a bromine.
I have taken advantage here that the integration of that signal is two, so it is a -CH2 group. You can pursue further to finish the problem.
2.195. Structure Assignment with NMR
A compound of formula C8 H9 Br has 1 H nmr signals: 2.01 δ (d, 3), 5.14 δ (q, 1) and 7.35
δ (broad s, maybe g, 5). What is the compound? HINTS: 1. Always use ihd and pursue.
2.“g” means a mess as we will see if we haven’t yet; treat it as “no knowledge” for now.
To start the pursuit (which could start in lots of different ways), I notice the ihd suggests
a benzene, and I find confirmation in the signal at 7.35 δ. Pursuing, I see the area is 5
and that the total area is 9, which is consistent with the total number of hydrogen atoms.
Therefore the benzene ring has only one substituent on it. You finish it.
2.196. Structure Assignment with NMR
A compound of the formula C5 H10 O2 has four 1 H nmr signals: 1.14 δ (t, J=7.7, 3), 1.26 δ
(t, J=7.2, 3), 2.32 δ (q, J=7.7, 2), and 4.13 δ (q, J=7.2, 2), What is the compound?
2.197. Structure Assignment with NMR
A compound of the formula C7 H14 O has 1 H nmr signals: 1.06 δ (s, 6), 2.15 δ (s, 2), and
2.33 δ (s, 1.4), What is the compound? HINT: Use the rule as modified in the last problem.
2.198. Structure Assignment with NMR
A compound of the formula C5 H10 O2 has two 1 H nmr signals: 1.14 δ (s, 9), 11.49 δ (broad
singlet, exchangeable, 1), What is the compound? HINT: “Exchangeable” means a hydrogen
atom that rapidly comes on and off the site of the organic molecule; it usually means a -OH
or a -NH2 .
Chm 222
Exercise Set 2
2.206
27
2.199. Splitting from Multiple Sources, Case 1
Imagine a situation where a -CH2 - has a methyl group on both sides. That can be (is or
must be,in this case) like having six hydrogen atoms on neighboring carbon atoms. Our
rule from problem 181 must be modified slightly in this case: it becomes (n+n’+1) where
n is the number of neighboring hydrogen atoms on one side and n’ is the number on the
other. In this case it would be (3+3+1), and we would see a septet splitting pattern. What
might be the splitting of a -CH2 - which had three hydrogen atom next to it on one side and
one on the other side? HINT: The conditional “might,” “can be,” are because of a problem
we will get to.
2.200. Structure Assignment with NMR
A compound of the formula C7 H14 O has 1 H nmr signals: 0.9 δ (t, 3), 1.1 δ (d, 6), 1.6 δ
(sextet, 2), 2.42 δ (t, 2), and 2.6 δ (heptet, 1), What is the compound? HINT: Apply the
rule from the last problem.
2.201. Splitting from Multiple Sources, Case 2
Our (n+n’+1) rule, see problem 199, breaks down when the size of the coupling of the n
hydrogen atoms is not the same as the splitting of the n’ hydrogen atoms and the chemical
shift difference is small. Under this circumstance, you get a multiplet (indicated by a “m”),
a mess (also a “m”), or, as called by those less proficient in the language, garbage (indicated
by a “g”). You can learn little from the spin-spin coupling of such a peak except that it
is coupled to two (or more) different hydrogen atoms. The following is an example: A
compound of the formula C5 H10 O2 has four 1 H nmr signals: 0.99 δ (d, 6), 2.12 δ (m, 1),
2.23 δ (d, 2), and 11.9 δ (broad singlet, exchangeable, 1), What is the compound? HINT:
This is a beauty for pursuit. The 0.99 δ peak is a doublet; hence coupled to one hydrogen
atom. Pursue! Where is that one hydrogen atom? It must be the 2.12 δ peak, as that is
the only one with an integration of 1. Pursue! The 2.12 δ peak is a multiplet, hence must
be coupled to some other set of hydrogen atoms. Those others must be the 2.23 δ peak, as
it is the only other peak that is split (and remember, if A splits B, B must split A). You
continue.
2.202. Structure Assignment with NMR
A compound of the formula C9 H11 Br has 1 H nmr signals: 2.2 δ (quintet, 2), 2.75 δ (t, 2),
3.35 δ (t, 2), and 7.2-7.5 δ (g, 5), What is the compound? HINT: Apply the rule from the
last problem.
2.203. Structure Assignment with NMR
A compound of the formula C9 H8 O2 has 1 H nmr signals: 5.4 δ (d, 1, J=15), 7.2-7.5 δ (g,
5), 7.8 δ (d, 1, J=15), and 12.4 δ (s, 1, exchanges with D2 O), What is the compound?
2.204. Structure Assignment with NMR
You have two compounds with the formula C10 H12 O. The first has 1 H nmr signals: 1.18 δ
(t, 1.5), 2.4 δ (s, 1.5), 2.95 δ (q, 1), 7.24 δ (d, 1), and 7.8 δ (d, 1). The second has 1 H nmr
signals: 1.31 δ (t, 3.1), 2.65 δ (s, 2.9), 2.75 δ (q, 2.0), 7.3 δ (d, 1.95), and 7.8 δ (d, 2.1).
HINT: You will need to use Table 1 carefully to be successful in obtaining an answer.
2.205. Using NMR to Distinguish Isomers
How would you use 1 H nmr to distinguish between 2,3-dimethylbutane and 2,2-dimethylbutane?
Remember that integration is relative only, so it cannot be used absolutely.
Chm 222
Exercise Set 2
2.216
28
2.206. Using NMR to Distinguish Molecules
How would you use 1 H nmr to distinguish between diethylether and ethyl-methyl ether?
Remember that integration is relative only, so it cannot be used absolutely.
2.207. Using NMR to Distinguish Isomers
How would you use 1 H nmr to distinguish between 3,6-dimethyl-1,4-cyclohexadiene and
1,3-dimethyl-1,4-cyclohexadiene? Remember that integration is relative only, so it cannot
be used absolutely.
2.208. Using NMR to Distinguish Isomers
How would you use 1 H nmr to distinguish between 1-methylethanol (isopropanol) and
propanol? Remember that integration is relative only, so it cannot be used absolutely.
2.209. Using NMR to Distinguish Isomers
How would you use 1 H nmr to distinguish between 1,2,3-trichloropropane and 1,1,1-trichloropropane?
Remember that integration is relative only, so it cannot be used absolutely.
2.210. Using NMR to Distinguish Molecules
How would you use 1 H nmr to distinguish between 2,2-dimethylbutane and 37? Remember
that integration is relative only, so it cannot be used absolutely.
2.211. Splitting from Multiple Sources, Case 3
Problems 199 and 201 outline two situations where spin-spin coupling occurs from more
than one source. There is a third case. If the n hydrogen atoms on one side of the site on
which we are focussed and the n’ hydrogen atoms on the other side have sufficiently different
J values and the chemical shift is large enough, we then see an (n+1)(n’+1) pattern. That
is, we see, for instance, a doublet of triplets. A (d of t) means you have three major peaks,
each of which is a doublet. The (n+1)(n’+1) pattern often occurs when one of the couplings
is long range (more than three bonds away), which is rare. An example: A compound of
formula C5 H8 has 1 H nmr signals: 1.00 δ (t, 3), 1.55 δ (sextet, 2), 1.94 δ (t, 1), and 2.15 δ
(t of d, 2). What is the compound?
2.212. Prediction of NMR Spectrum
Predict the 1 H nmr spectrum for 4,4’-dimethyl-1-pentyne. HINTS: (1) This compound
exhibits (n+1)(n’+1) peaks through the triple bond. (2) See problem 211.
2.213. Spectroscopic Identification
A compound of formula C4 H8 Br2 has IR, 2850-3000 cm−1 and a 1 H nmr of 1.87 δ (s, 9.1),
3.86 δ (s, 3.0). What is it?
2.214. Spectroscopy and Learning Organic Chemistry
A compound of formula C9 H18 O has IR, 1710 cm−1 and a 1 H nmr of 1.2 δ. What is it?
HINT: Here is my initial reaction for you to pursue. The IR suggests a carbonyl group and
the nmr suggests that the molecule is highly symmetrical–only one nmr signal. Take it from
there. Pursue!
2.215. Spectroscopic Identifcation
A compound of formula C2 H4 Cl2 has IR, 2850-3000 cm−1 and a 1 H nmr of 2.1 δ (d), 5.9 δ
(q). What is it? HINT: Use ihd and pursue.
Chm 222
Exercise Set 2
2.225
29
Table 4:
13 C
Chemical Shifts
Environment
Alkanes
Alkenes and Aromatics
Alkynes
Carbonyl
Not aldehydes or ketones
Aldehydes and ketones
Chemical Shift, δ
0 to 60
100 to 170
60 to 90
160-190
190-220
All downfield with Electronegative substituents
2.216. Spectroscopic Identification
A compound of formula C3 H6 Br2 has IR, 2850-3000 cm−1 and a 1 H nmr of 2.4 δ (quintet),
3.5 δ (t). What is it?
2.217. Spectroscopic Identificaton
A compound of formula C5 H10 O2 has IR, 1740 cm−1 and a 1 H nmr of 1.15 δ (t, 3), 1.25 δ
(t, 3), 2.3 δ (q, 2), and 4.32 δ (q, 2). What is it? HINT: The 1.15 δ (t, 3) signal must be
next to one of the two signals with integration of 2. Pursue!
2.218. Spectroscopic Identification
A compound of formula C6 H14 O has IR, 2850-3000 cm−1 and a broad band at 3200 cm−1 .
It has a 1 H nmr of 0.8 δ (t, 6), 1.0 δ (s, 3), 1.5 δ (q, 4), and 1.6 δ (s, 1). What is it? HINT:
The 0.8 δ signal must be next to the 1.5 δ signal, as they are the only things split. Pursue!
2.219. Spectroscopic Identification
A compound of formula C6 H14 O has nothing of interest in the IR. The 1 H nmr has peaks
at 1.1 δ (d, 30) and 3.6 δ (heptet, 5). What is it?
2.220. Spectroscopic Identification
A compound of formula C8 H12 O has a IR with prominent peaks at 1685 cm−1 (broad and
strong), 1625 cm−1 (sharp), 3105 cm−1 , and 2950-3000 cm−1 . The 1 H nmr has a doublets at
6.7 and 5.85 δ, both with integrations of 1, triplets at 1.87 and 2.47 δ, both with integrations
of 2, and a singlet at 1.16 δ with an integration of 6. Identify the compound.
2.221. 13 C NMR
Predict the decoupled
13 C
nmr of ethanal.
2.222. 13 C NMR
Predict the decoupled
13 C
nmr of 3-butene-2-one.
2.223. 13 C NMR
Predict the decoupled
13 C
nmr of 2-butanol.
2.224. 13 C NMR and Off Resonance Decoupling
Predict the position and splitting of the 13 C nmr peaks in 2-butanol with off resonance
decoupling.
Chm 222
Exercise Set 2
2.232
30
2.225. 13 C NMR Spectroscopic Identification
A compound of the formula C4 H8 O has four 13 C nmr signals: 7.87 δ (q), 29.43 δ (q),
36.87 δ (t), and 209.28 δ (s) where the values in parenthesis are the off-resonance decoupled
splittings. What is the compound?
2.226. 13 C NMR Spectroscopic Identification
A compound of the formula C6 H12 has 13 C nmr signals at 17 δ, 25 δ, and 138 δ. What is
the compound?
2.227. 13 C NMR Spectroscopic Identification
A compound of the formula C7 H7 Br has seven decoupled 13 C nmr signals: 21.05 δ, 122.31
δ 127.65 δ, 128.48 δ, 129.70 δ 132.06 δ, and 140.07 δ. What are possible identifications of
the compound?
2.228. Choice of Spectral Method
Which method(s), IR, mass spectroscopy, 1 H nmr, or 13 C nmr would you use to distinguish
between 61 and 62? Explain your answer.
2.229. Choice of Spectral Method
Which method(s), IR, mass spectroscopy, 1 H nmr, or 13 C nmr would you use to distinguish
between 63 and 64? Explain your answer.
2.230. Choice of Spectral Method
Which method(s), IR, mass spectroscopy, 1 H nmr, or 13 C nmr would you use to distinguish
between 65 and 66? Explain your answer.
2.231. Spectroscopic Identification
A compound has five 13 C nmr peaks: 11.97 δ, (q), 25.90 δ, (t), 132.10 δ (d), 160.24 δ, (d)
and 194.09 δ (d) [splitting patterns from off-resonance decoupling] and five 1 H nmr peaks:
1.13 δ (t, 3), 2.38 δ (quintet, 2), 6.12 δ (d of d, 1), 6.942 δ (d of t, 1), and 9.52 δ (d, 1).
What is the compound?
Chm 222
Exercise Set 2
2.239
31
2.232. Spectroscopic Identification and Learning Organic Chemistry
A compound has an IR with interesting peaks at 3082 and 3060 cm−1 as well as 1621 cm−1 .
The 1 H nmr has peaks at 5.225, 5.737, 6.692, and between 7.1 and 7.5 δ. The first two are
doublets with an integration of 1, the third is a doublet of doublets with an integration of
1, and the last is a mess (sometimes called garbage) with an integration of 5. The 13 C nmr
has 6 peaks at 113.7, 126.2, 127.8, 128.5, 137.0, and 137.6 δ. What is the compound? How
do we analyze this? The bunch of 1 H nmr peaks in the region of 7.1 to 7.5 δ catch my eye.
Likely a benzene ring. Pursue! Area is 5 which suggests a monosubstituted benzene ring.
Pursue! That would mean that there are four kinds of carbon in the ring, accounting for
four of the 13 C peaks. The two that are left (no matter which two you choose) are in the
region of sp2 hybrid carbon atoms, suggesting another double bond. Take it from there and
pursue!
2.233. Spectroscopic Identification
A compound with formula C4 H8 O2 has a 1 H nmr with a broad singlet at 12.2 δ, a heptet
at 2.6 δ, and a doublet at 1.21 δ. What is the compound?
2.234. Spectroscopic Identification
A compound of formula C3 H6 O has IR, 1730 cm−1 and a 1 H nmr of 1.11 δ (t), 2.46 δ (g)
and 9.79 δ (t). What is it?
2.235. Spectroscopic Identification
A compound of formula C5 H8 O2 has a 1 H nmr with a triplet at 1.1 δ, a singlet at 2.32 δ,
and a quartet at 2.78 δ. The relative integrations are 3, 3, and 2, respectively. What is the
compound?
2.236. Spectroscopic Identification and Learning Organic Chemistry
A compound with a formula C7 H12 O2 has an IR band at 1746 cm−1 and 1 H nmr peaks at
1.8 δ (m, 2), 2.12 δ (d of t, 2), 2.41 δ (t, 2), 3.76 δ (s, 3), 4.9 δ (m, 2) and 5.68 δ (m, 1).
The 13 C nmr has peaks at 23, 34, 35 δ, all decoupled triplets, 51 δ (q), 115.9 δ (t), 137 δ
(d), and 174.9 δ (s). What is the compound? The ihd is 2 and the 1746 cm−1 suggests
a carbonyl. Pursue. This is verified by the 174.9 peak, which further demands it has an
adjacent oxygen (it is too low in the 13 C spectrum for a ketone or aldehyde). Continuing
to pursue. The only peak in the hydrogen spectrum that could be attached to that -O- of
the -C(O)O- group is the 3.76 δ peak which is a methyl group. So we have a -C(O)COCH3 .
That ends that pursuit. On to another. The 137 and 115.9 δ peaks are an alkene, as are
those (I pursue) at 4.9 and 5.68 δ. The integration of the former indicates a terminal alkene.
You can finish it.
2.237. Spectroscopic Identification
A compound of the empirical formula C4 H8 O has three 1 H nmr signals: 1.06 δ (d, 6); 2.39
δ (garbage, 1), and 9.57 δ (d,1). What is the compound?
2.238. Spectroscopic Identification
A compound has the formula C4 H8 O2 ; IR 1730 cm−1 . The 1 H nmr has peaks at 2.1 δ (s,
31), 3.4 δ (s, 30), and 3.9 δ (s, 18.8). What is the compound?
Chm 222
Exercise Set 2
2.250
32
2.239. Spectroscopic Identification
A compound with the empirical formula C4 H8 O2 has an 1 H nmr spectrum: triplet at 1.27
δ (1.0), singlet at 2.03 δ (1.05), quartet at 4.11 δ (0.68). What is the compound?
2.240. Spectroscopic Identification
A compound of formula C9 H12 has IR, 2850-3150 cm−1 and a 1 H nmr of 1.25 δ (d, 6), 2.95
δ (heptet, 1) and 7.3 δ (g, 5). What is it?
2.241. Spectroscopic Identification
A compound with formula C4 H8 O has four 13 C nmr peaks: 37.11 δ, (t), 61.61 δ, (t), 117.21
δ (t), and 135.02 δ (d) [splitting patterns from off-resonance decoupling] and six 1 H nmr
peaks: 2.318 δ (g, 2), 2.76 δ (broad, exchanges, 1), 3.65 δ (t, 2), 5.10 δ (d of d, 1), 5.13 δ
(d of d, 1), and 5.82 δ (g, 1). What is the compound?
2.242. Spectroscopic Identification and Learning Organic Chemistry
A compound with the formula C9 H13 N has an 1 H nmr spectrum as follows: 2.25 δ (s, 6), 3.43
δ, (s, 2), 7.32 δ, (g, 5). What is the compound? The ihd is 4. I would first guess, therefore,
a benzene ring. Pursue. That is consistent with the signal at 7.32 δ, whose integration
(pursuing) suggests a monosubstituted benzene ring. End of that pursuit. The signal at
2.25 δ with integration of 6 suggests two methyl groups. Pursue. They are deshielded and
hence probably on the N. You can take it from there.
2.243. Spectroscopc Identification
A compound with formula C7 H14 O has six 13 C nmr peaks: 13.81 δ, 17.24 δ, 18.23 δ, 40.80
δ, 42.26 δ and 214.77 δ [decoupled] and five 1 H nmr peaks: 0.96 δ (t, 3), 1.09 δ (d, 6), 1.59
δ (sextet, 2), 2.42 δ (t, 2), and 2.61 δ (heptet, 1). What is the compound?
2.244. Spectroscopc Identification
A compound with formula C5 H9 N has four 13 C nmr peaks: 21.79 δ (q), 25.98 δ, (d), 26.13
δ (t), and 118.89 δ (s) [off-resonance decoupled] and three 1 H nmr peaks: 1.07 δ (d, 6), 2.02
δ (nonet, 1), and 2.23 δ (d, 2). What is the compound?
2.245. Spectroscopc Identification
A compound with formula C6 NO2 ClH4 has an 1 H nmr with two peaks, a doublet at 7.4 δ
and another doublet at 8.2 δ. What is the compound?
2.246. Learning Organic Chemistry
Make a list of the steps you would take to determine the identity of a compound given the
1 H nmr spectrum of the compound. Could you change the order of attack? How?
2.247. IR Review
How would you use IR to distinguish between cyclohexane and trans-2-hexene.
2.248. 1 H NMR Review
How would you use 1 H nmr to distinguish between cyclohexane and trans-2-hexene.
2.249. 13 C NMR Review
How would you use 13 C nmr to distinguish between cyclohexane and trans-2-hexene.
Chm 222
Exercise Set 2
2.258
33
2.250. Equivalent Hydrogen Atoms and 1 H NMR
Find a structure for a nine carbon compound (with only hydrogen atoms in addition) whose
1 H nmr has two singlets.
2.251. Using Your Knowledge to Predict NMR Signal Structure
The proton nmr of CHD2 I consists of a five line pattern with intensities 1:2:3:2:1. HINT:
D has a spin of 1, which means the spin projection could be 1, 0, or -1 for each of the two
D. Justify this splitting of the proton spectrum.
2.252. Using Your Knowledge to Understand NMR Spectra
The 1 H nmr of N,N-dimethylformamide has signals at 2.9 δ, 3.0 δ, and 8.0 δ. Explain.
2.253. Using Your Knowledge to Predict Chemical Shifts
The compound, 18-annulene, 39, has 1 H nmr signals at 8.9 δ (s, 12) and -1.8 δ (s, 6).
Explain. HINT: That really is a minus sign!
2.254. Spectroscopc Identification
A compound with formula C6 H14 O has four 13 C nmr peaks: 17.7 δ, 26.4 δ, 38.9 δ, and
73.0 δ and four 1 H nmr peaks: 0.90 δ (d, 6), 1.10 δ (s, 6), 1.25 δ (broad, disappears upon
treatment with D2 O), (s, 1), and 1.3 δ (heptet, 1). What is the compound?
2.255. Using Your Knowledge to Understand NMR Spectra
The proton nmr spectrum of 2,2,3,3-tetrachlorobutane is a function of temperature. At
room temperature, it exhibits a single peak. At low temperatures, a pair of peaks, rather
closely spaced, are found. Explain.
2.256. Review–Typical First Exam Questions
Give the zigzag line structure, and indicate the hybridization at each carbon atom, for
pent-3-ene-2-one.
2.257. Review–Typical First Exam Questions*
Sketch or describe the highest occupied molecular orbital (HOMO) on the molecule of the
previous question.
Chm 222
Exercise Set 2
2.270
34
2.258. Review–Typical First Exam Questions**
Are there any other electron pairs in pent-3-ene-2-one that are relatively loosely held? Is
so, how would you describe those electrons? HINT: For instance, σ electrons between C1
and C2 .
2.259. Review–Typical First Exam Questions***
At what site (or sites) might a nucleophile such as H− attack pent-3-ene-2-one?
2.260. Review–Typical First Exam Questions
If we look at a benzene ring which lies in the x,y plane, what hybridization is used by a
carbon atom in that molecule? Be specific in stating what orbitals are used in making those
hybrid orbitals? What orbital(s) is(are) not used for the hybrid orbitals?
2.261. Review–Typical First Exam Questions
Is a π bond stronger or weaker than a σ bond? Explain briefly. Draw something.
2.262. Review–Typical First Exam Questions
Make a drawing of the most stable conformer of 1-chloropropane?
2.263. Review–Typical First Exam Questions
Make a drawing of a less stable form of 1-chloropropane that could be isolated at low
temperatures. HINT: I do NOT want a diagram of a material on the “top of an energy
mountain.”
2.264. Review–Typical First Exam Questions
Use epwa to illustrate the following reaction: BH–4 reacts with pentanal, followed by treatment with H+ .
2.265. Review–Typical First Exam Questions
Use epwa to illustrate the following reaction: A mole of ethyl Grignard with a mole of 40.
2.266. Review–Typical First Exam Questions
Use epwa to illustrate the following reaction: A mixture of 40 with excess 41, followed by
H+ .
2.267. Review–Typical First Exam Questions
How would you make 2-methyl-3-pentanol from compounds containing 3 carbon atoms (or
fewer)? Use epwa to explain your reasoning.
2.268. Review–Typical First Exam Questions
A compound of formula C4 H10 O has an IR with peaks between 2800-3000 cm−1 and no
other interesting peaks above 1500 cm−1 . The 1 H nmr has four peaks: 3.34 δ (t, 2), 3.33
δ (s, 3), 1.59 δ (sextet, 2), and 0.93 δ (t, 3). What is the compound? HINT: For partial
credit you must given your reasoning.
2.269. Review–Typical First Exam Questions
A compound has a M+. of 121, an IR as given in Figure 4, a 13 C nmr with peaks at 151 δ,
129 δ, 117 δ, 113 δ, and 40.5 δ, and a 1 H nmr with peaks at 2.89 δ (s, 1.7) and 6.6 to 7.4 δ
(g, or m, 1.4). What is the compound? HINT: For partial credit you must given reasoning.
Chm 222
Exercise Set 2
2.270
35
Figure 4: IR for Problem 269
Chm 222
Exercise Set 2
2.276
36
2.270. Review–Typical First Exam Questions
A compound of formula C4 H7 ClO has an IR with peaks between 2800 and 3000 cm−1 and
at 1720 cm−1 . The 1 H nmr has three peaks: 3.45 δ (t, 2), 3.07 δ (t, 2), and 2.14 δ (s, 3).
What is the compound? HINT: For partial credit you must give your reasoning.
2.271. Review–Typical First Exam Questions
A compound has a mass spectrum with peaks at 120 and 122, intensities of 0.31 and 0.09,
respectively, and an IR with peaks between 3000 and 2800 cm−1 . The 13 C nmr has peaks
at 18 δ, 30 δ, 40 δ, and 75 δ, and the 1 H nmr has peaks at 1.02 δ (d, 18.3), 1.54 δ (s, 17.9),
and 1.89 δ (heptet (septet), 3.1). What is the compound? HINT: For partial credit you
must give reasoning.
2.272. Review–Typical First Exam Questions
What is the HOMO of C2 H2 ClBr3 ? HINT: I do NOT want you to do an m.o. diagram.
Figure it out logically. This is an easy problem.
2.273. Review–Typical First Exam Questions
Use epwa to show how the reaction of propyl Grignard, 4, with 5 occurs. NOTE: After
reaction, the solution is treated with acid solution.
2.274. Review–Typical First Exam Questions
Draw a line (or zig-zag) structure for a compound with an IR spectrum with a broad peak
at 3340 cm−1 and a peak at 1710 cm−1 . Then draw a line (or zig-zag) structure for a
compound with an IR spectrum with a peak at 3230 cm−1 , a weak peak at 2330 cm−1 . and
a peak at 1660 cm−1 .
2.275. Review–Typical First Exam Questioins
For each of the following reactions, check the side that dominates at equilibrium (the side
”to which the reaction occurs”).
CH–3
HCCH
=
CH4
HCC–
+
HF
+
OH–
=
F–
+
H2 O
HI
+
NH–2
=
I–
+
NH3
H2 S
+
NH–2
=
HS–
AsH–2
=
HSe–
H2 Se
Chm 222
+
+
+
+
NH3
AsH3
Exercise Set 2
2.279
37
Table 5: Data for problem 277
13 C
1H
δ
δ
1.2
1.6
2.2
2.7
3.8
3.95
15
20
30
31
58
204
Splitting
d
q
s
quintet
t
s (exchanges)
Integration
0.70
0.50
0.74
0.24
0.51
0.26
Table 6: Data for problem 278
13 C
δ
24
30
32
135
137
139
141
204
206
1H
δ
1.3
2.4
2.7
7.0
7.2
Splitting
t
s
q
d
d
Integration
6
6
4
4
4
2.276. Review–Typical First Exam Questions
Here is a sequential series of reactions. Give the structure of the overall product of the
reaction, that is, the compound at the end of step 5.
1. Bromobenzene, C6 H5 Br is treated with Mg metal in ether.
2. The product of step 1 is mixed with butanal.
3. The product of step 2 is treated with H+ and the neutral compound isolated.
4. The product of step 3 is reacted with PCC.
5. The product of step 4 is reacted with methyl Grignard and then treated with acid.
2.277. Review–Typical First Exam Questions
A compound of formula C6 H12 O2 has the 1 H and 13 C spectra shown in Table 5. What is
the compound? HINT: For partial credit you must give reasoning. That doesn’t mean you
have to write paragraphs: ”A triplet, so this hydrogen has 7 neighbors . . . ” would do if it
wasn’t nonsense.
2.278. Review–Typical First Exam Questions
A compound of has a mass spectrum with a molecular ion peak of 176. It has an IR peaks
at 3101 cm−1 , 1725 cm−1 , and 1640 cm−1 . The nmr data is given in the Table 6. What is
the compound? HINT: For partial credit you must give reasoning; and since you have lots
of data, there is a lot of reasoning to be given.
Chm 222
Exercise Set 2
2.280
38
2.279. Review–Typical First Exam Questions
Use epwa to show the reaction of ethyl Grignard, CH3 CH2 MgBr, with 6, followed by treatment with acid. HINT: We haven’t studied this reaction (yet), but you should be able to
figure out what happens from what you should know.
2.280. Spectral Identification
A compound has a M+. peak of 168. The IR has interesting peaks at 3050, 1700(strong),
and 1620 cm−1 . The 1 H has peaks at 0.9 (d, J=8, 11.7) δ, 1.1(s, 18.1) δ, 1.48(nonet, J=8,
1.95) δ, 2.3(d, J=8, 4.03) δ, 6.08 (d, J=18, 3.9) δ, and 6.9 (d, J=18, 4.01) δ. What is the
compound?
Chm 222
Exercise Set 2