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# 5.9: Problems for Chapter 5

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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.

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This page titled 5.9: Problems for Chapter 5 is shared under a not declared license and was authored, remixed, and/or curated by Tim Soderberg.