5.9: Problems for Chapter 5
- Page ID
- 2350
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P5.1: For each molecule, predict the number of signals in the 1H-NMR and the 13C-NMR spectra (do not count split peaks - eg. a quartet counts as only one signal). Assume that diastereotopic groups are non-equivalent.
P5.2: For each of the 20 common amino acids, predict the number of signals in the proton-decoupled 13C-NMR spectrum.
P5.3: Calculate the chemical shift value (expressed in Hz, to one decimal place) of each sub-peak on the 1H-NMR doublet signal below. Do this for:
a) a spectrum obtained on a 300 MHz instrument
b) a spectrum obtained on a 100 MHz instrument
P5.4: Consider a quartet signal in an 1H-NMR spectrum obtained on a 300 MHz instrument. The chemical shift is recorded as 1.7562 ppm, and the coupling constant is J = 7.6 Hz. What is the chemical shift, expressed to the nearest 0.1 Hz, of the furthest downfield sub-peak in the quartet? What is the resonance frequency (again expressed in Hz) of this sub-peak?)
P5.5: One easily recognizable splitting pattern for the aromatic proton signals from disubstituted benzene structures is a pair of doublets. Does this pattern indicate ortho, meta, or para substitution?
P5.6 :Match spectra below to their corresponding structures A-F.
Structures:
Spectrum 1
δ | splitting | integration |
4.13 | q | 2 |
2.45 | t | 2 |
1.94 | quintet | 1 |
1.27 | t | 3 |
Spectrum 2
δ | splitting | integration |
3.68 | s | 3 |
2.99 | t | 2 |
1.95 | quintet | 1 |
Spectrum 3
δ | splitting | integration |
4.14 | q | 1 |
2.62 | s | 1 |
1.26 | t | 1.5 |
Spectrum 4
δ | splitting | integration |
4.14 | q | 4 |
3.22 | s | 1 |
1.27 | t | 6 |
1.13 | s | 9 |
Spectrum 5
δ | splitting | integration |
4.18 | q | 1 |
1.92 | q | 1 |
1.23 | t | 1.5 |
0.81 | t | 1.5 |
Spectrum 6
δ | splitting | integration |
3.69 | s | 1.5 |
2.63 | s | 1 |
P5.7: Match spectra 7-12 below to their corresponding structures G-L .
Structures:
Spectrum 7:
δ | splitting | integration |
9.96 | d | 1 |
5.88 | d | 1 |
2.17 | s | 3 |
1.98 | s | 3 |
Spectrum 8:
δ | splitting | integration |
9.36 | s | 1 |
6.55 | q | 1 |
2.26 | q | 2 |
1.99 | d | 3 |
0.96 | t | 3 |
Spectrum 9:
δ | splitting | integration |
9.57 | s | 1 |
6.30 | s | 1 |
6.00 | s | 1 |
1.84 | s | 3 |
Spectrum 10:
δ | splitting | integration |
9.83 | t | 1 |
2.27 | d | 2 |
1.07 | s | 9 |
Spectrum 11:
δ | splitting | integration |
9.75 | t | 1 |
2.30 | dd | 2 |
2.21 | m | 1 |
0.98 | d | 6 |
Spectrum 12:
δ | splitting | integration |
8.08 | s | 1 |
4.13 | t | 2 |
1.70 | m | 2 |
0.96 | t | 3 |
P5.8: Match the 1H-NMR spectra 13-18 below to their corresponding structures M-R .
Structures:
Spectrum 13:
δ | splitting | integration |
8.15 | d | 1 |
6.33 | d | 1 |
Spectrum 14: 1-723C (structure O)
δ | splitting | integration |
6.05 | s | 1 |
2.24 | s | 3 |
Spectrum 15:
δ | splitting | integration |
8.57 | s (b) | 1 |
7.89 | d | 1 |
6.30 | d | 1 |
2.28 | s | 3 |
Spectrum 16:
δ | splitting | integration |
9.05 | s (b) | 1 |
8.03 | s | 1 |
6.34 | s | 1 |
5.68 | s (b) | 1 |
4.31 | s | 2 |
Spectrum 17:
δ | splitting | integration |
7.76 | d | 1 |
7.57 | s (b) | 1 |
6.44 | d | 1 |
2.78 | q | 2 |
1.25 | t | 3 |
Spectrum 18:
δ | splitting | integration |
4.03 | s | 1 |
2.51 | t | 1 |
2.02 | t | 1 |
P5.9: Match the 1H-NMR spectra 19-24 below to their corresponding structures S-X.
Structures:
Spectrum 19:
δ | splitting | integration |
9.94 | s | 1 |
7.77 | d | 2 |
7.31 | d | 2 |
2.43 | s | 3 |
Spectrum 20:
δ | splitting | integration |
10.14 | s | 2 |
8.38 | s | 1 |
8.17 | d | 2 |
7.75 | t | 1 |
Spectrum 21:
δ | splitting | integration |
9.98 | s | 1 |
7.81 | d | 2 |
7.50 | d | 2 |
Spectrum 22:
δ | splitting | integration |
7.15-7.29 | m | 2.5 |
2.86 | t | 1 |
2.73 | t | 1 |
2.12 | s | 1.5 |
Spectrum 23:
δ | splitting | integration |
7.10 | d | 1 |
6.86 | d | 1 |
3.78 | s | 1.5 |
3.61 | s | 1 |
2.12 | s | 1.5 |
Spectrum 24:
δ | splitting | integration |
7.23-7.30 | m | 1 |
3.53 | s | 1 |
P5.10: Match the 1H-NMR spectra 25-30 below to their corresponding structures AA-FF.
Structures:
Spectrum 25:
δ | splitting | integration |
9.96 | s | 1 |
7.79 | d | 2 |
7.33 | d | 2 |
2.72 | q | 2 |
1.24 | t | 3 |
Spectrum 26:
δ | splitting | integration |
9.73 | s | 1 |
7.71 | d | 2 |
6.68 | d | 2 |
3.06 | s | 6 |
Spectrum 27:
δ | splitting | integration |
7.20-7.35 | m | 10 |
5.12 | s | 1 |
2.22 | s | 3 |
Spectrum 28:
δ | splitting | integration |
8.08 | s | 1 |
7.29 | d | 2 |
6.87 | d | 2 |
5.11 | s | 2 |
3.78 | s | 3 |
Spectrum 29:
δ | splitting | integration |
7.18 | d | 1 |
6.65 | m | 1.5 |
3.2 | q | 2 |
1.13 | t | 3 |
Spectrum 30:
δ | splitting | integration |
8.32 | s | 1 |
4.19 | t | 2 |
2.83 | t | 2 |
2.40 | s | 3 |
P5.11: Match the 1H-NMR spectra 31-36 below to their corresponding structures GG-LL
Structures:
Spectrum 31:
δ | splitting | integration |
6.98 | d | 1 |
6.64 | d | 1 |
6.54 | s | 1 |
4.95 | s | 1 |
2.23 | s | 3 |
2.17 | s | 3 |
Spectrum 32:
δ | splitting | integration |
7.08 | d | 1 |
6.72 | d | 1 |
6.53 | s | 1 |
4.81 | s | 1 |
3.15 | 7-tet | 1 |
2.24 | s | 3 |
1.22 | d | 6 |
Spectrum 33:
δ | splitting | integration |
7.08 | d | 2 |
6.71 | d | 2 |
6.54 | s | 1 |
3.69 | s | 3 |
3.54 | s | 2 |
Spectrum 34:
δ | splitting | integration |
9.63 | s | 1 |
7.45 | d | 2 |
6.77 | d | 2 |
3.95 | q | 2 |
2.05 | s | 3 |
1.33 | t | 3 |
Spectrum 35:
δ | splitting | integration |
9.49 | s | 1 |
7.20 | d | 2 |
6.49 | d | 2 |
4.82 | s | 2 |
1.963 | s | 3 |
Spectrum 36:
δ | splitting | integration |
9.58 | s(b) | 1 |
9.31 | s | 1 |
7.36 | d | 1 |
6.67 | s | 1 |
6.55 | d | 1 |
2.21 | s | 3 |
2.11 | s | 3 |
P5.12: Use the NMR data given to deduce structures.
a ) Molecular formula: C5H8O
1H-NMR:
δ | splitting | integration |
9.56 | s | 1 |
6.25 | d (J~1 Hz) | 1 |
5.99 | d (J~1 Hz) | 1 |
2.27 | q | 2 |
1.18 | t | 3 |
13C-NMR
δ | DEPT |
194.60 | CH |
151.77 | C |
132.99 | CH2 |
20.91 | CH2 |
11.92 | CH3 |
b) Molecular formula: C7H14O2
1H-NMR:
δ | splitting | integration |
3.85 | d | 2 |
2.32 | q | 2 |
1.93 | m | 1 |
1.14 | t | 3 |
0.94 | d | 6 |
13C-NMR
δ | DEPT |
174.47 | C |
70.41 | CH2 |
27.77 | CH |
27.64 | CH2 |
19.09 | CH3 |
9.21 | CH3 |
c) Molecular formula: C5H12O
1H-NMR:
δ | splitting | integration |
3.38 | s | 2H |
2.17 | s | 1H |
0.91 | s | 9H |
13C-NMR
δ | DEPT |
73.35 | CH2 |
32.61 | C |
26.04 | CH3 |
d) Molecular formula: C10H12O
1H-NMR:
δ | splitting | integration |
7.18-7.35 | m | 2.5 |
3.66 | s | 1 |
2.44 | q | 1 |
1.01 | t | 1.5 |
13C-NMR
δ | DEPT |
208.79 | C |
134.43 | C |
129.31 | CH |
128.61 | CH |
126.86 | CH |
49.77 | CH2 |
35.16 | CH2 |
7.75 | CH3 |
P5.13:
13C-NMR data is given for the molecules shown below. Complete the peak assignment column of each NMR data table.
a)
δ | DEPT | carbon # |
161.12 | CH |
|
65.54 | CH2 |
|
21.98 | CH2 |
|
10.31 | CH3 |
|
b)
δ | DEPT | carbon # |
194.72 | C |
|
149.10 | C |
|
146.33 | CH |
|
16.93 | CH2 |
|
14.47 | CH3 |
|
12.93 | CH3 |
|
c)
δ | DEPT | carbon # |
171.76 | C |
|
60.87 | CH2 |
|
58.36 | C |
|
24.66 | CH2 |
|
14.14 | CH3 |
|
8.35 | CH3 |
|
d)
δ | DEPT | carbon # |
173.45 | C |
|
155.01 | C |
|
130.34 | CH |
|
125.34 | C |
|
115.56 | CH |
|
52.27 | CH3 |
|
40.27 | CH2 |
|
e)
δ | DEPT | carbon # |
147.79 | C |
|
129.18 | CH |
|
115.36 | CH |
|
111.89 | CH |
|
44.29 | CH2 |
|
12.57 | CH3 |
|
P5.14: You obtain the following data for an unknown sample. Deduce its structure.
1H-NMR:
13C-NMR:
Mass Spectrometry:
P5.15:You take a 1H-NMR spectrum of a sample that comes from a bottle of 1-bromopropane. However, you suspect that the bottle might be contaminated with 2-bromopropane. The NMR spectrum shows the following peaks:
δ | splitting | integration |
4.3 | septet | 0.0735 |
3.4 | triplet | 0.661 |
1.9 | sextet | 0.665 |
1.7 | doublet | 0.441 |
1.0 | triplet | 1.00 |
How badly is the bottle contaminated? Specifically, what percent of the molecules in the bottle are 2-bromopropane?
Challenge problems
C5.1: All of the 13C-NMR spectra shown in this chapter include a signal due to CDCl3, the solvent used in each case. Explain the splitting pattern for this signal.
C5.2: Researchers wanted to investigate a reaction which can be catalyzed by the enzyme alcohol dehydrogenase in yeast. They treated 4'-acylpyridine (1) with living yeast, and isolated the alcohol product(s) (some combination of 2A and 2B).
a) Will the products 2A and 2B have identical or different 1H-NMR spectra? Explain.
b) Suggest a 1H-NMR experiment that could be used to determine what percent of starting material (1) got turned into product (2A and 2B).
c) With purified 2A/2B, the researchers carried out the subsequent reaction shown below to make 3A and 3B, known as 'Mosher's esters'. Do 3A and 3B have identical or different 1H-NMR spectra? Explain.
d) Explain, very specifically, how the researchers could use 1H-NMR to determine the relative amounts of 2A and 2B formed in the reaction catalyzed by yeast enzyme.