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ChemWiki: The Dynamic Chemistry E-textbook > Organic Chemistry > Organic Chemistry With a Biological Emphasis > Chapter 5: Structure Determination II: Nuclear Magnetic Resonance Spectroscopy > Section 5.P: Problems for Chapter 5

Section 5.P: Problems for Chapter 5

Table of Contents

Link to Solution Manual

 

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.

image142.png

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

 

image144.png

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:

image145.png

 

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:

image148.png

 

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:

image150.png

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:

image152.png

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:

 

image154.png

 

 

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:

 

image155a.png

 

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)

image158.png

 

δ

DEPT

carbon #

161.12

CH

 

65.54

CH2

 

21.98

CH2

 

10.31

CH3

 

 

b)

image160.png

 

δ

DEPT

carbon #

194.72

C

 

149.10

C

 

146.33

CH

 

16.93

CH2

 

14.47

CH3

 

12.93

CH3

 

 

 

c)

image162.png

 

δ

DEPT

carbon #

171.76

C

 

60.87

CH2

 

58.36

C

 

24.66

CH2

 

14.14

CH3

 

8.35

CH3

 

 

d)

image164.png

 

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)

image166.png

 

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:

image168.png

13C-NMR:

 

 image169.jpg

Mass Spectrometry:

image171.png

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).

image174.png

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.

image176.png

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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Last Modified
08:40, 2 Oct 2013

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