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5.P: Problems for Chapter 5

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    1064
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    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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