LSW F02
Organic Chemistry Exam II notes
Spectroscopy
Empirical Formula:
Chemical Formula:
Index of Hydrogen Deficiency (IHD)
A)From a structure:
B)From a molecular formula, CcHhNnOoXx,
Formula for saturated hydrocarbons:
Subtract the number of hydrogens the compound has:
Subtract the number of halogens the compound has:
The Oxygen is ignored:
For Nitrogen add one H:
Multiply by 0.5:
What is the IHD of the following molecular formulas?
C6H6
C4H8O
C4H9N
C6H10
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C2Cl2
LSW F02
Organic Chemistry Exam II notes
Electromagnetic Radiation (EMR):
Wave-like properties:
Particle-like properties:
Energy States:
Quantization of Energy:
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LSW F02
Organic Chemistry Exam II notes
Infra red (IR) spectroscopy
Vibrations of covalent bonds within a molecule
Vibrations:
IR region spectrum
Two regions:
•
4000-1000 cm-1 known as the functional group region, and
•
< 1000 cm-1 known as the fingerprint region
•
functional group region:
•
fingerprint region:
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LSW F02
Organic Chemistry Exam II notes
Hookes' Law
1. stronger bond (larger k value), υ increases.
increasing bond strength compare:
C-C
C=C
C≡C
C-C-H
C=C-H
C≡C-H
2. heavier atoms attached (larger m value), υ decreases.
increasing reduced mass:
C-H
C-C
C-Cl
C-Br
C-I
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LSW F02
Organic Chemistry Exam II notes
Bond
Base Strength /
Comments
Value Shape
1
C=O
1715
s, "finger"
2
O-H
3600
s, brd
3
N-H
3500
m
4
C-O
1100
s
5
C=C
1650
w alkene
aroma
tic
m-s
6
C≡C
2150
w, sharp
7
C-H
3000
s
8
C≡N
2250
m, sharp
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LSW F02
Organic Chemistry Exam II notes
Sample IR Spectra:
toluene
Acetone (2-propanone)
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LSW F02
Organic Chemistry Exam II notes
2-propanol:
Butanoic acid
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LSW F02
Organic Chemistry Exam II notes
Methyl acetate or methyl ethanoate:
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LSW F02
Organic Chemistry Exam II notes
Nuclear Magnetic Resonance (NMR):
1
H NMR or proton NMR or PMR or just NMR
13
C NMR or CMR
Only certain molecules can show absorbance in NMR
What is happening:
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LSW F02
Organic Chemistry Exam II notes
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LSW F02
Organic Chemistry Exam II notes
Chemical Shift
• NMR spectrum:
•
Resonance:
•
Chemical shift:
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LSW F02
Organic Chemistry Exam II notes
Calculate the chemical shift of a peak that occurs 655.2 Hz
downfield of TMS on a spectrum recorded using a 90 MHz
spectrometer ?
Calculate the frequency of the chemical shift of
chloroform (CHCl3, δ=7.28 ppm) relative to TMS on a
spectrum recorded on a 300 MHz spectrometer?
Shielding in 1H-NMR
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LSW F02
Organic Chemistry Exam II notes
Factors which affect chemical shift:
Electronegativity:
Compound, X
CH3X
CH3F
CH3OH
CH3Cl
CH3Br
CH3I
CH4
(CH3)4Si
F
O
Cl
Br
I
H
Si
Electronegativity
of X
4.0
3.5
3.1
2.8
2.5
2.1
1.8
Cumulative
effect
CH2Cl2
CHCl3
Chemical
shift
δ / ppm
4.26
3.4
3.05
2.68
2.16
0.23
0
5.30
7.27
Distance
effect
CH2CH2CH2Br
67
1.25
1.69
3.30
LSW F02
Organic Chemistry Exam II notes
Magnetic Anisotropy
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LSW F02
Organic Chemistry Exam II notes
Hydrogen Bonding
D2O (deuterium oxide) exchange experiment.
1
H-NMR Chemical shifts
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LSW F02
Organic Chemistry Exam II notes
I
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LSW F02
Organic Chemistry Exam II notes
1
Coupling in H-NMR
CH3 with CH next door
Cl
Cl
H
Cl
H
H
H
H
Cl
H
H
H
Ho
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LSW F02
Organic Chemistry Exam II notes
CH with CH3 next door
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LSW F02
Organic Chemistry Exam II notes
1,1-dichloroethane:
•
δ = 5.9 ppm
•
δ = 2.1 ppm
Coupling Constant, J
Pascal's Triangle
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LSW F02
Organic Chemistry Exam II notes
Predicting Spectra
Predict the spectrum for propane including multiplicity
and the relative intensities in propane (CH3CH2CH3).
How many
different types
of hydrogen?
What is the
chemical
shift?
What is the
integration?
What is the
multiplicity?
What are the
intensities?
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LSW F02
Organic Chemistry Exam II notes
Complex Coupling Patterns
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Organic Chemistry Exam II notes
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1
Organic Chemistry Exam II notes
Interpreting H-NMR Spectra
How many types of H?
What types of H?
How many H of each type are there?
What is the connectivity?
Integration
Coupling
77
how many groups of signals in the spectra
chemical shift of each group
integration (relative area) for each group.
coupling patterns.
LSW F02
Organic Chemistry Exam II notes
Peak Chemical Integration Equivalent Multiplicity Neighboring
Hydrogens
Hydrogens
Shift (δ)
ppm
A
B
C
D
E
78
Possible
Group
circle the H