1121792871 organic chemistry 1

Chapter Nine

MULTIPLE CHOICE QUESTIONS

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2Difficulty Level: Easy

1. How many signals would you expect to find in the 1H NMR spectrum of CH3OCH2CH2OCH3?

A) 1B) 2C) 3D) 4E) 5

Ans: B

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2Difficulty Level: Easy

2. Predict the splitting pattern you would observe for the proton at C1 of 2,3-dimethyl-2-phenylbutane.

A) DoubletB) SingletC) QuartetD) SeptetE) Octet

Ans: B

545

Topic: Proton NMR- Symmetry, Splitting, Chemical ShiftSection: 9.2Difficulty Level: Easy

3. Which one of the following best represents the predicted approximate chemical shift and coupling for the hydrogen(s) indicated with the arrow?

OCH3

A) 1.10 ppm, singletB) 2.10 ppm, doubletC) 3.40 ppm, singletD) 4.5 ppm, singletE) 3.5 ppm, quartet

Ans: C



O

A) 1.00 ppm, singletB) 2.10 ppm, singletC) 2.10 ppm, quartetD) 3.00 ppm, singletE) 2.10 ppm, triplet

Ans: B

546


5. Which one of the following best represents the predicted approximate chemical shift and coupling for the hydrogen(s) indicated with the arrow?O

A) 1.00 ppm, quartetB) 2.40 ppm, singletC) 2.40 ppm, quartetD) 3.00 ppm, quartetE) 2.40 ppm, triplet

Ans: C


6. Which one of the following best represents the predicted approximate chemical shift and coupling for the hydrogen(s) indicated with the arrow?O

A) 1.00 ppm, quartetB) 2.40 ppm, singletC) 2.40 ppm, quartetD) 3.00 ppm, quartetE) 1.00 ppm, triplet

Ans: E

547



H

H

A) 5.40 ppm, multipletB) 2.00 ppm, multipletC) 2.00 ppm, doubletD) 2.00 ppm, quartetE) 5.40 ppm, doublet

Ans: A



H

H

A) 5.40 ppm, doubletB) 1.00 ppm, multipletC) 2.00 ppm, doubletD) 1.00 ppm, doubletE) 5.40 ppm, multiplet

Ans: D

548



N

A) 3.00 ppm, doubletB) 3.00 ppm, tripletC) 5.00 ppm, tripletD) 1.00 ppm, doubletE) 5.40 ppm, multiplet

Ans: B



N

A) 3.00 ppm, doubletB) 3.00 ppm, tripletC) 5.00 ppm, tripletD) 1.00 ppm, doubletE) 3.00 ppm, singlet

Ans: E

549


11. For the following compound how many different signals would you see in the proton NMR? (Assume that you can see them all.)

A) 4B) 5C) 6D) 7E) 8

Ans: A



H3CO

A) 4B) 5C) 6D) 7E) 8

Ans: C

550



A) 1B) 2C) 3D) 4E) 5

Ans: C


14. A downfield ( 9-10) singlet is observed in the 1H NMR spectrum of:A)

CH3CCH2CH3

O

B)

C6H5CH2C O

H

C)

(CH3)2CHC O

H

D)

(CH3)3CC O

H

E)

C6H5CH2CCH3

O

Ans: D

551

Topic: Proton NMR- Symmetry, Splitting, Chemical ShiftSection: 9.2Difficulty Level: Medium


A) 1B) 2C) 3D) 4E) 5

Ans: D



O

A) 4B) 5C) 6D) 7E) 8

Ans: B

552



OCH3

A) 1.10 ppm, singletB) 2.10 ppm, tripletC) 3.40 ppm, tripletD) 4.5 ppm, singletE) 5.3 ppm, doublet

Ans: D

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2Difficulty Level: Medium



Ans: A

553


19. How many 1H NMR signals would trans-1,2-dichlorocyclopropane give?A) 1B) 2C) 3D) 4E) 5

Ans: B


20. How many chemically distinct 1H NMR signals are there in the following compound?

A) 1B) 2C) 3D) 4E) 5

Ans: D


21. How many 1H NMR signals would cis-1,2-dichlorocyclopropane give?A) 1B) 2C) 3D) 4E) 5

Ans: C

554


22. How many 1H NMR signals would you expect from this compound?

A) 1B) 2C) 3D) 4E) 5

Ans: B


23. The 1H NMR spectrum of which of these compounds would consist of a triplet, singlet and quartet only?

A) 2-chloro-4-methylpentaneB) 3-chloro-2-methylpentaneC) 3-chloropentaneD) 1-chloro-2,2-dimethylbutaneE) 3-chloro-3-methylpentane

Ans: E


555


H

H

A) 1.00 ppm, doubletB) 2.00 ppm, singletC) 2.00 ppm, tripletD) 2.00 ppm, doubletE) 1.00 ppm, triplet

Ans: D


25. A compound C5H11Cl which exhibits only two singlets in the 1H NMR spectrum must be:

A) 1-ChloropentaneB) 1-Chloro-2,2-dimethylpropaneC) 1-Chloro-2-methylbutaneD) 3-ChloropentaneE) 1-Chloro-3-methylbutane

Ans: B


26. Consider the expected 1H NMR spectrum of 1,1,3,3-tetramethylcyclopentane. Which of the following is likely to be observed?

A) 7 signals: all singletsB) 7 signals: 4 singlets, 3 doubletsC) 3 signals: all singletsD) 3 signals: one singlet, 2 doubletsE) 3 signals: two singlets, one doublet

Ans: C


556

27. Consider the expected 1H NMR spectrum of 2,4-dimethyl-1,4-pentadiene. Which of the following is likely to be observed?

A) 7 signals: all singletsB) 4 signals: all singletsC) 3 signals: all singletsD) 3 signals: one singlet, 2 doubletsE) 4 signals: two singlets, two doublets

Ans: E

Topic: Proton NMR- Symmetry, Splitting, Chemical ShiftSection: 9.2Difficulty Level: Hard

28. For the C2 methylene group in 1-bromopropane, the theoretical multiplicity in the 1H NMR spectrum, presuming that Jab is sufficiently different from Jbc and that the instrument has sufficient resolving power, is which of these?

CH3 CH2 CH2 Br

c b a

A) 2B) 5C) 6D) 8E) 12

Ans: E

Topic: Structure Elucidation Section: 2.16, 9.2Difficulty Level: Medium

557

29. An organic compound absorbs strongly in the IR at 1687 cm-1. Its 1H NMR spectrum consists of two signals, a singlet at 2.1 ppm and a multiplet centered at 7.1 ppm. Its mass spectrum shows significant peaks at m/z 120, m/z 105 and m/z 77. This information is consistent with which of the following structures?

A) IB) IIC) IIID) IVE) V

Ans: A

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2ADifficulty Level: Easy

30. If all the protons of 1-fluoropentane could be discerned, which would you expect to be at the lowest field in the 1H NMR spectrum of this compound?

A) Protons on carbon IB) Protons on carbon IIC) Protons on carbon IIID) Protons on carbon IVE) Protons on carbon V

Ans: A

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2ADifficulty Level: Hard

558

31. The 1H NMR signal for which of the indicated protons occurs farthest downfield?


Ans: E

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2CDifficulty Level: Easy

32. Which proton(s) of the compound below would appear as a septet in the 1H NMR spectrum?

A) The protons on carbon IB) The protons on carbon IIC) The protons on carbon IIID) The protons on carbon IVE) The protons on carbon V

Ans: B

559


33. Which proton(s) of the compound below would appear as a doublet in the 1H NMR spectrum?

A) The protons on carbon IB) The protons on carbon IIC) The protons on carbon IIID) The protons on carbon IVE) The protons on carbon V

Ans: A


34. Which proton(s) of the compound below would appear as a triplet in the 1H NMR spectrum?

A) The protons on carbon IIB) The protons on carbon I and VC) The protons on carbon III and VD) The protons on carbon III and IVE) The protons on carbon V

Ans: C

560

Topic: Proton NMR- Symmetry, Splitting, Chemical shiftSection: 9.2CDifficulty Level: Easy

35. Consider the expected splitting of signal “b” in the 1H NMR spectrum of 1-methoxy-2-methylpropane, shown below. Presuming that Jab is sufficiently different from Jbc and that the instrument has sufficient resolving power, what is the theoretical multiplicity of signal “b”?

A) 8B) 9C) 12D) 21E) 24

Ans: D

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2CDifficulty Level: Medium



Ans: D

Topic: Proton NMR- Symmetry, Splitting, Chemical Shift

561

Section: 9.2CDifficulty Level: Medium

37. Which of these compounds will not be represented by a singlet only in the 1H NMR spectrum?

A) NeopentaneB) HexamethylbenzeneC) IsobutaneD) (Z)-1,2-DichloroetheneE) (E)-1,2-Dichloroethene

Ans: C

Topic: Proton NMR- Symmetry, Splitting, Chemical ShiftSection: 9.2CDifficulty Level: Hard

38. Consider the expected splitting of the C2 proton signal in the 1H NMR spectrum of 1,1-dibromopentane. Presuming that the coupling constants for neighboring protons are sufficiently different, and that the instrument has sufficient resolving power, what is the theoretical multiplicity of the C2 proton signal?

A) 3B) 4C) 5D) 6E) 8

Ans: D


562

39. Consider the expected splitting of signal “b” in the 1H NMR spectrum of N-methyl-1-propanamine, shown below. Presuming that Jab is sufficiently different from Jbc and that the instrument has sufficient resolving power, what is the theoretical multiplicity of signal “b”?

A) 2B) 5C) 6D) 8E) 12

Ans: E


40. Consider the expected splitting of signal “b” in the 1H NMR spectrum of 1,1-dichloro-3-methylbutane, shown below. Presuming that Jab is sufficiently different from Jbc and that the instrument has sufficient resolving power, what is the theoretical multiplicity of signal “b”?

A) 8B) 9C) 12D) 18E) 21

Ans: E

Topic: Proton NMR- Symmetry, Splitting, Chemical shiftSection: 9.2CDifficulty Level: Hard

563

41. Consider the expected splitting of signal “b” in the 1H NMR spectrum of 1,2-dimethoxypropane, shown below. Presuming that Jbc is sufficiently different from Jbd and that the instrument has sufficient resolving power, what is the theoretical multiplicity of signal “b”?

A) 2B) 5C) 6D) 8E) 12

Ans: E


42. Consider the expected splitting of signal “c” in the 1H NMR spectrum of 2-ethyl-1-butanol, shown below. Presuming that Jbc is sufficiently different from Jcd and that the instrument has sufficient resolving power, what is the theoretical multiplicity of signal “c”?

A) 6B) 7C) 8D) 12E) 15

Ans: E


564

43. Consider the expected splitting of the C2 proton signal in the 1H NMR spectrum of 2-ethyl-1,3-propanediol. Presuming that the coupling constants for neighboring protons are sufficiently different, and that the instrument has sufficient resolving power, what is the theoretical multiplicity of the C2 proton signal?

A) 6B) 7C) 8D) 12E) 15

Ans: E


44. What is the theoretical multiplicity of the C-2 proton signal in the 1H NMR spectrum of 2-hydroxymethyl-1,3-propanediol, shown below?

A) 1B) 6C) 7D) 8E) 9

Ans: C

565

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2CDifficulty Level: Hard

45. Consider the 1H NMR spectrum of very pure 1-propanol. Assuming the maximum multiplicity of signals and non-superposition of peaks, what is the expected signal splitting pattern for each signal, in the order (a, b, c, d) ?

A) 3, 6, 4, 1B) 3, 6, 4, 3C) 3, 12, 3, 1D) 3, 12, 3, 3E) 3, 12, 6, 3

Ans: E

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2, 9.2CDifficulty Level: Medium

46. The 1H NMR spectrum of which of the compounds below, all of formula C7H12O2, would consist of two singlets only?

A) I

B) IIC) IIID) IVE) V

Ans: E

566

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2, 9.2CDifficulty Level: Hard

47. The 1H NMR spectrum of which of the compounds below, all of formula C7H12O2, would consist of three singlets only?

A) I


Ans: B

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.2, 9.2CDifficulty Level: Hard

48. The 1H NMR spectrum of which of the compounds below, all of formula C7H12O2, would consist of a singlet, a doublet and a triplet only?

A) I


Ans: D

567

Topic: Proton NMR- Unknown IdentificationSection: 9.2, 9.2A, 9.2CDifficulty Level: Medium

49. A compound with the molecular formula C4H10O gives a 1H NMR spectrum consisting only of a quartet centered at 3.5 and a triplet at 1.1. The most likely structure for the compound is:

A)

CH3COH

CH3

CH3B)

CH3OCHOH

CH3

C) CH3CH2CH2CH2OHD) CH3CH2OCH2CH3E) CH3CHCH2OH

CH3Ans: D

568

Topic: Proton NMR- Unknown IdentificationSection: 9.2, 9.3Difficulty Level: Easy

50. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C9H14O? IR data shows no characteristic peak around 1700 cm-1. The 13C-NMR chemical shifts (ppm): 108.4, 50.9, 31.6, 23.5, 2.0. Relative integration is known.

0123PPM

6

2

3 3

A) OO

B) O

OC)

O

O

D)

O

O

E)

O OAns: C

569


51. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C9H10O2? Relative integration is shown.

024681012PPM

1

5

2

2

A) CHO

B) CO2H

C) CO2H

D)

HO2C

E) CO2H

Ans: C

570


52. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C8H14? Relative integration is shown.

012345678PPM

2

9

3

A)

B)

C) C

D)

E)

Ans: D

571


53. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C6H11N? In the IR spectrum you notice a stretch at about 2250 cm-1. Relative integration is shown.

012345678PPM

1

4

6

A) CNB)

C) CN

D) CN

E)

NH

Ans: D

572

Topic: Proton NMR- Unknown IdentificationSection: 9.2, 9.3Difficulty Level: Medium

54. Determine the most likely structure of a compound, with the molecular formula C9H12, which gave a 1H NMR spectrum consisting of: a doublet at 1.25 a septet at 2.90 and a multiplet at 7.25

I II III IV V]


Ans: D


55. A compound with the molecular formula C10H13Cl gave the following 1H NMR spectrum: singlet, 1.6 singlet, 3.1 multiplet, 7.2 (5H)The most likely structure for the compound is:


Ans: B

573


56. A compound with the molecular formula C8H9BrO gave the following 1H NMR spectrum: triplet, 1.4 quartet, 3.9 multiplet, 7.0 (4H)There was no evidence of an -OH band in the IR spectrum. A possible structure for the compound is:


Ans: C


574

57. A compound with the molecular formula C6H15N gave the following 1H NMR spectrum: triplet, 0.90 quartet, 2.4There were no other signals. The most likely structure for the compound is:

A) CH3NCH2CH3

CH2CH2CH3B) CH3NCH2CH2CH2CH3

CH3C) CH3CH2CH2CH2CH2CH2NH2D) CH3CH2NCH2CH3

CH2CH3E) CH3CH2CH2NCH2CH2CH3

HAns: D


58. A compound with the molecular formula C8H9ClO gave the following 1H NMR spectrum: triplet, 3.7 triplet, 4.2 multiplet, 7.1There was no evidence of an -OH band in the IR spectrum. The most likely structure for the compound is:


Ans: A

Topic: Proton NMR- Unknown IdentificationSection: 9.2, 9.3

575

Difficulty Level: Medium

59. A compound with the molecular formula C3H6Cl2 gave a 1H NMR spectrum consisting only of a triplet centered at 3.7 and a quintet centered at 2.2. The most likely structure for the compound is:

A) CH3CH2CHCl2

B) CH3CHClCH2ClC) ClCH2CHClCH3

D) ClCH2CH2CH2ClE) CH3CCl2CH3

Ans: D


576


012345678PPM

23

A)

B)

C)

D)

E)

Ans: C

577


61. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C4H8O? Relative integration is shown.

012345678PPM

1 1

A)

OB)

OHC) OH

D) O

E) O

Ans: D

578


62. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C7H12O4? The 13C-NMR spectrum shows peaks at 14.1, 40.8, 61.0 and 166.8 ppm. Relative integration is shown.

012345PPM

2

1

3

A) O O

O OB)

OO

H H

C)OO

O OD) O

O

O

O

E)

O

O

O

OAns: A

579


63. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C10H11N? Looking at the 13C-NMR you notice 10 distinct peaks, and the IR has a characteristic peak around 2250 cm-1. Relative integration is shown.

012345678PPM

4

2 23

A)

B)

NCC)

CN

D)

CNE) H

N

Ans: D

580


64. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C6H10O2? The 13C-NMR shows characteristic chemical shifts at 22.3, 31.1, 117.3, 157.7, and 171.6 ppm. Relative integration is shown.

012345678910111213PPM

exchanges w/ D2O

1

1 1 1

6

A)HO

O

B) CO2H

C) O

OD) CO2H

E) CO2H

Ans: E

581


65. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C11H14O2? Looking at the 13C-NMR you notice a peak at 174 ppm. Relative integration is shown.

012345678PPM

2 2 2

3

23

A)

O

O

B) OO

C) O

OD)

O

OE)

O

OAns: A

582

Topic: Proton NMR- Unknown Identification.Section: 9.2, 9.3Difficulty Level: Medium

583

66. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C12H17NO and a characteristic IR stretch near 1700 cm-1 and a characteristic peak in the 13C-NMR at 170 ppm? Relative integration is shown.

012345678PPM

22

3

2

3

2

3

A) O

N

B)N

OC)

HO

N

D) O

N

E) O

N

Ans: A

584


67. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C9H18O2 and characteristic 13C-NMR peaks at 11.3, 21.6, 25.3, 49.4, 67.1, and 175.5 ppm? Relative integration is shown.

0123456PPM

1 1

2

3 3

A)O

O

B)

O

O

C)

O

D)

O

O

E)

OO

Ans: B

585



01234567891011PPM

1

2 2 2 23

A) CHO

O

B) O

O

C) CO2H

D) CO2H

E) CO2H

Ans: C

586



012PPM

1

2 2 2

6

3

A) O

B)

H

O

C) OH

D)

OE) O

Ans: E

587



0123456PPM

1

2 2 2

3

A)

O

O

B)O

H

O

C)

O

O

D)

O

O

E) O

OHAns: D

588



01234567PPM

exchanges with D2O

2 2

1

2 2

3

A) O

B) HO

C)

HO

D) OH

E)

HOAns: E

589


72. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C5H8O? The IR spectrum does show a characteristic stretch around 1700 cm-1. Relative integration is shown.

012345678PPM

1 1

33

A)O

B) O

C)O

D) O

E) O

Ans: E

590


73. A compound C5H10O gave the following spectral data:1 H NMR spectrum IR spectrumdoublet, 1.10 strong peaksinglet, 2.10 near 1720 cm-1

septet, 2.50Which is a reasonable structure for the compound?


Ans: E


74. A compound C4H9Br gave the following 1H NMR spectrum:triplet, 1.0 (3H); doublet, 1.7; multiplet, 1.8; multiplet, 4.1 (1H)Which is a reasonable structure for the compound?

A) CH3CH2CHBrCH3

B) CH3CH2CH2CH2BrC) (CH3)2CHCH2BrD) (CH3)3CBr

Ans: A

591

Topic: Proton NMR- Unknown IdentificationSection: 9.2, 9.3Difficulty Level: Hard

75. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C6H12O which shows no characteristic stretches in the IR between 3600-3300 cm-1, but does around 1600 cm-1? Relative integration is shown.

0123456PPM

1 1 1

3

6

A) O

B) O

C)

OD) O

E) O

Ans: A

592


76. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C5H11NO, which shows a characteristic stretch in the IR around 1700 cm-1, and a characteristic peak at 202 ppm in the 13C-NMR? Relative integration is shown.

012345678910PPM

1

2

6

2

A)H2N

CHO

B)N

CHOC)

N

OD)

NH

CHO

E)

N CHO

Ans: B

593


594

77. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C8H15ClO3, which shows a characteristic stretch in the IR around 1750 cm-1 but not around 3500 cm-1, and a characteristic peak at 173 ppm in the 13C-NMR? Relative integration is shown.

01234PPM

1

4

2 2

6

A)

Cl

O

O

O

B)

O

O

Cl

O

C)

Cl

O

O

O

D) O

OCl

O

E)

O

O

O

ClAns: C

595



0246810PPM

2 2 2

3 3

A) O

OB)

HO

O

C) O

D) O

OE)

O

O

Ans: D

Topic: Proton NMR- Unknown Identification

596

Section: 9.2, 9.3Difficulty Level: Hard


012345678PPM

21

3

6

A)

B)

C)

D)

E)Ans: B

597


80. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C4H7Br? Relative integration is shown.

0123456PPM

1 12

3

A) BrB) Br

C)

BrD) Br

E) Br

Ans: C

598


81. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C5H10O? The IR spectrum does not show any characteristic stretches around 1700 cm-1. Relative integration is shown.

01234567PPM

1 12

3 3

A) O

B) O

C)

O

D) O

E) OAns: A

599


82. What is the structure of the compound in the following 1H-NMR spectrum with the molecular formula C5H11NO? In the 13C-NMR spectrum you notice that the farthest peak downfield has a chemical shift of 173 ppm. Relative integration is shown.

0123456789PPM

exchanges with D2O

1

3 32 2

A)

NH

O

B)

NH

O

C)

NH

O

D)

O

HN

E)

H N

O

Ans: A

600


83. A compound with the molecular formula C10H14 gave the following 1H NMR spectrum: doublet, 1.2 singlet, 2.3 septet, 2.8 multiplet, 7.1A possible structure for the compound is:


Ans: B

601


84. Determine the likely structure for a compound A (C6H10O), which is found to decolorize bromine in carbon tetrachloride. Its spectral data is as follows: 1 H NMR IR triplet, 1.0 singlet, 2.4 2200 cm-1 (sharp) singlet, 1.4 singlet, 3.4 3300 cm-1 (sharp) quartet, 1.6 3500 cm-1 (broad)


Ans: C

602

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.8BDifficulty Level: Easy

85. In NMR terminology, protons Ha and Hb are said to be:

A) IdenticalB) EnantiotopicC) DiastereotopicD) HomotopicE) Mesotopic

Ans: C

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.8BDifficulty Level: Easy

86. In the structure shown, Ha and Hb are classified as:

A) homotopic protons.B) vicinal protons.C) enantiotopic protons.D) diastereotopic protons.E) isomeric protons.

Ans: C

Topic: Proton NMR- Chemical Shift, Splitting, Etc.Section: 9.8BDifficulty Level: Medium



Ans: D

603




Ans: D


89. In the structure shown, Hb and Hc are classified as:

A) homotopic protons.B) geminal protons.C) enantiotopic protons.D) diastereotopic protons.E) isomeric protons.

Ans: D

604

Topic: C-13 NMR- Symmetry, Chemical ShiftSection: 9.11Difficulty Level: Easy

90. The broadband proton-decoupled 13C NMR spectrum of a hexyl chloride exhibits five signals. Which of these structures could be the correct one for the compound?

A)

CH3CCH2CH2Cl

CH3

CH3B)

CH3CH2CCH2CH3

Cl

CH3C)

CH3C CHCH3

CH3

Cl

CH3

D)

CH3CHCHCH2CH3

CH3

ClE)

CH3C CHCH3

CH3

CH3 Cl

Ans: D


91. How many signals will be recorded in the broadband proton-decoupled 13C spectrum of 4-chloro-1-ethylbenzene?

A) 2B) 3C) 4D) 6E) 7

Ans: D

605


92. How many 13C signals would 1,4-dimethylbenzene give?

A) 1B) 2C) 3D) 4E) 5

Ans: C


93. How many 13C signals would 1,3-dichlorobenzene give?

A) 1B) 2C) 3D) 4E) 5

Ans: D


94. How many 13C signals would 1,2-dimethylbenzene give?

A) 1B) 2C) 3D) 4E) 5

Ans: D

606


95. How many 13C signals would you expect from anisole?

A) 1B) 2C) 3D) 4E) 5

Ans: E

Topic: Carbon NMR- Symmetry, Chemical ShiftSection: 9.11Difficulty Level: Easy

96. For the following compound how many different signals would you see in the carbon NMR? (Assume that you can see them all.)

A) 3B) 4C) 5D) 6E) 7

Ans: C

607

Topic: Carbon NMR- Symmetry, Chemical ShiftSection: 9.11Difficulty Level: Easy

97. In 13C NMR spectroscopy, the signal due to this type of carbon occurs furthest downfield.

A) –CNB)

C O

C)C O

D)C X

E) –CC–Ans: B

Topic: C-13 NMR- Symmetry, Chemical ShiftSection: 9.11Difficulty Level: Medium

98. The C7 compound which gives 3 signals in the broadband proton-decoupled 13C spectrum could be:

A) HeptaneB) 2-MethylhexaneC) 3,3-DimethylpentaneD) 2,4-DimethylpentaneE) 2,2,3-Trimethylbutane

Ans: D

608

Topic: Carbon NMR- Symmetry, Chemical ShiftSection: 9.11Difficulty Level: Medium


A) 1B) 2C) 3D) 4E) 5

Ans: E



A) 4B) 5C) 6D) 7E) 8

Ans: D

609



N

A) 3B) 4C) 5D) 8E) 9

Ans: A


102. A bromodichlorobenzene which gives four signals in the broadband proton-decoupled 13C spectrum could be:


Ans: A

610

Topic: Carbon NMR- Symmetry, Chemical ShiftSection: 9.11Difficulty Level: Hard


S S

A) 4B) 5C) 6D) 7E) 8

Ans: C

Topic: Carbon NMR and Proton NMR- Symmetry, Chemical ShiftSection: 9.2, 9.11Difficulty Level: Medium

104. Which compound below would give rise to 3 signals in the proton NMR spectrum and 4 signals in the carbon NMR spectrum? (Assume you can separate and see all peaks.)

I II III IV

Br

A) IB) IIC) IIID) IVE) None of the above.

Ans: E

611

Topic: Carbon NMR and Proton NMR- Symmetry, Chemical ShiftSection: 9.2, 9.11Difficulty Level: Hard


I II III IV

Br

A) IB) IIC) IIID) IVE) More than one of the above.

Ans: C



I II III IV

Br

A) IB) IIC) IIID) IVE) More than one of the above.

Ans: A

612


107. Which compound below would NOT give rise to 4 signals in the proton NMR spectrum and 3 signals in the carbon NMR spectrum? (Assume you can separate and see all peaks.)

OH OH

OH

OH

I II III IV

A) IB) IIC) IIID) IVE) All of the above fit the criteria.

Ans: C



I II III IV

Br

A) IB) IIC) IIID) IVE) None of the above.

Ans: D

613

Topic: C-13 NMR- Symmetry, Chemical ShiftSection: 9.11DDifficulty Level: Easy

109. How will the methyl carbon appear in the proton off-resonance decoupled 13C spectrum of toluene?

A) SingletB) DoubletC) TripletD) QuartetE) Quintet

Ans: D

Topic: Mass SpectrometrySection: 9.13Difficulty Level: Easy

110. Which is the base peak?A) 15B) 29C) 44D) 45E) 100

Ans: B

614


111. Which is the likely molecular ion (M)?

A) 15B) 29C) 44D) 45E) 100

Ans: C


112. A prominent (M-18) peak suggests that the compound might be a(n):

A) AlkaneB) AlcoholC) EtherD) KetoneE) Primary amine

Ans: B

Topic: Mass SpectrometrySection: 9.16Difficulty Level: Medium

113. Predict the base peak for 2-chloro-2-methylpropaneA) m/z 15B) m/z 92C) m/z 43D) m/z 57E) m/z 77

Ans: D

615


114. Select the structure of a compound C6H14 with a base peak at m/z 43.A) CH3CH2CH2CH2CH2CH3

B) (CH3CH2)2CHCH3

C) (CH3)3CCH2CH3

D) (CH3)2CHCH(CH3)2

E) None of theseAns: D


115. What is the molecular formula of this compound?

m/z intensity 84 M

10.00 85 0.56 86 0.04

A) C5H10OB) C5H8OC) C5H24

D) C6H12

E) C4H6O2

Ans: B


116. What is the molecular formula of this compound?

m/z intensity 78 M

10.00 79 1 80 3.3 81 0.3

A) C6H6

B) C3H5ClC) C6H8

D) C6H9

E) C3H7ClAns: E

616

Topic: Mass SpectrometrySection: 9.17ADifficulty Level: Easy

117. The mass spectra of alkyl bromides and chlorides are characterized by an unusually intense __________.

A) base peakB) parent peakC) M

peakD) M

+2 peakE) None of these

Ans: D

Topic: Mass SpectrometrySection: 9.17ADifficulty Level: Hard

118. The data below from the molecular ion region of the mass spectrum of a halogen-containing compound are consistent with the presence of what halogen(s) in the original compound?

intensity

M 51.0

M+2 100.0

M+4 49.0

A) One BrB) One ClC) One Br and one ClD) Two BrE) Two Cl

Ans: D

SHORT ANSWER QUESTIONS

Topic: GeneralSection: 9.1Difficulty Level: Easy

119. “NMR” stands for _______________________.Ans: nuclear magnetic resonance

617

Topic: Structure Elucidation Section: 9.2Difficulty Level: Medium

120. Briefly explain how you might distinguish between the following substances by comparing their 1H-NMR spectra:

Ans: The main difference would likely be in the chemical shift of the methine proton of the isopropyl group. The methine proton in I is likely to be more deshielded, and produce a signal (septet) at about 3.5 ppm, while the analogous proton in II is likely to be found, also as a septet, at about 2.3 ppm.

618



Ans: The main difference would likely be in the chemical shifts of the methine proton of the isopropyl group and the methylene proton closest to the ester function. The methine proton in I is likely to be more deshielded, and produce a signal (septet) at about 3.5 ppm, while the analogous proton in II is likely to be found, also as a septet, at about 2.3 ppm. By contrast, the methylene proton in II is likely to be more deshielded, and produce a signal (triplet) at about 3.4 ppm, while the analogous proton in II is likely to be found, also as a triplet, at about 2.2 ppm.

619



Ans: The main difference would likely be in the chemical shifts of the methine proton of the isopropyl group and the methylene proton closest to the amide function. The methine proton in I is likely to be more deshielded, and produce a signal (septet) at about 3.5 ppm, while the analogous proton in II is likely to be found, also as a septet, at about 2.3 ppm. By contrast, the methylene proton in II is likely to be more deshielded, and produce a signal (triplet) at about 3.4 ppm, while the analogous proton in II is likely to be found, also as a triplet, at about 2.2 ppm.

Topic: 1H NMRSection: 9.2Difficulty Level: Medium

123. Predict the 1H NMR spectrum of diethoxymethane, CH3CH2OCH2OCH2CH3.

Ans:

O O

>

~4.9 ppmsinglet

>

~3.4 ppmquartet

>

~3.4 ppmquartet

>

~1.2 ppmtriplet

>

~1.2 ppmtriplet

620

Topic: 1H NMRSection 9.2Difficulty Level: Medium

124. Predict the 1H NMR spectrum of 2-chloroethanal, CH2ClCHO.

Ans:

ClO>

4-5 ppmdoublet

>

9-10 ppmtriplet

Topic: 1H NMRSection: 9.2ADifficulty Level: Easy

125. Predict the number of signals in the 1H NMR spectrum of 2-methyl-2-pentanol.

Ans: Five

Topic: General, Chemical ShiftSection: 9.2ADifficulty Level: Medium

126. A shielded proton will absorb at a higher frequency (this is the ________ end of the spectrum); and a deshielded proton will absorb at a lower frequency (the _____________ end of the spectrum).Ans: upfield; downfield

621

Topic: General, Signal IntegrationSection: 9.2BDifficulty Level: Easy

127. When measuring the integral for a particular peak in the NMR spectrum, we are not interested in the peak height as much as in the ____________________.Ans: area under the peak

Topic: Structure Elucidation Section: 9.2, 9.3Difficulty Level: Easy

128. Examine the 1H NMR spectrum of 1-nitropropane, shown below. Assign the signals to the respective hydrogen atoms in the molecule.

Ans:

>

>

>

NO21.0 ppmtriplet

2.0 ppmsextet

4.3 ppmtriplet

622

Topic: Structure Elucidation Section: 2.16, 9.2, 9.3Difficulty Level: Medium

129. An unknown compound, A, has the formula C7H14O. Elucidate the structure of A by scrutinizing its IR, 1H NMR and 13C NMR spectra, shown below.

Ans:

4-Heptanone

623

Topic: GeneralSection: 9.4Difficulty Level: Easy

130. Which form of electromagnetic radiation possesses the least energy?Ans: radiofrequency radiation

Topic: Reference CompoundSection: 9.7Difficulty Level: Easy

131. What compound is used as the standard “zero” reference in both carbon and proton NMR?Ans: TMS or tetramethylsilane or (CH3)4 Si

Topic: General, Bond Rotation, Proton ExchangeSection: 9.10Difficulty Level: Medium

132. Name two rapid processes that occur in organic molecules.Ans: Rotation about C-C single bonds; chemical exchange of protons attached to

electronegative atoms

624

Topic: 13C NMR, Structure Elucidation Section: 9.11Difficulty Level: Medium

133. Interpret the following 13C/DEPT spectrum of a compound C5H10Br2: elucidate the structure and assign all the 13C resonances.

Ans:

Br Br

>

32 ppm

>

>

27 ppm

>

33 ppm

>

33 ppm

625

Topic: Structure ElucidationSection: 2.16, 9.2, 9.3, 9.11Difficulty Level: Medium

134. An unknown compound, C, has the formula C7H7Br. Elucidate the structure of C by scrutinizing its IR, 1H NMR and 13C NMR spectra, shown below.

626

Ans:

4-Bromotoluene

627

Topic: Structure Elucidation Section: 2.16, 9.2, 9.3. 9.11Difficulty Level: Medium

135. An unknown compound, F, has the formula C3H6O2. Elucidate the structure of F by scrutinizing its IR, 1H NMR and 13C NMR spectra, shown below.

628

Ans:

Propanoic acid

629

Topic: Structure Elucidation Section: 2.16, 9.2, 9.3, 9.11Difficulty Level: Medium

136. An unknown compound, L, has the formula C5H10O2. Elucidate the structure of L by scrutinizing its IR, 1H NMR and 13C NMR spectra, shown below.

Ans:

Methyl butyrate

630

Topic: Structure Elucidation Section: 2.16, 9.2, 9.3, 9.11Difficulty Level: Hard

137. An unknown compound, I, has the formula C3H7NO2. Elucidate the structure of I by scrutinizing its IR, 1H NMR and 13C NMR spectra, shown below.

Ans:

1-Nitropropane

631


138. An unknown compound, E, has the formula C6H12O. Elucidate the structure of E by scrutinizing its IR, 1H NMR and 13C NMR spectra, shown below.

Ans:

2-Hexanone

632


633

139. An unknown compound, U, has the formula C6H4Cl2O. Elucidate the structure of U by scrutinizing its IR, 1H NMR and 13C NMR spectra, shown below.

634

Ans:

2,6-dichlorophenol

635


140. An unknown compound, V, has the formula C8H10O. Elucidate the structure of V by scrutinizing its IR, 1H NMR and 13C NMR spectra, shown below.

636

Ans:

2,6-dimethylphenol

637

Topic: Base Peak Section: 9.13Difficulty Level: Easy

141. In mass spectrometry, the most intense peak is assigned an intensity of 100%, and is referred to as the ______________.Ans: base peak

Topic: m/z Ratio Section: 9.13Difficulty Level: Easy

142. A mass spectrometer sorts ions on the basis of their _______________.Ans: mass to charge ratio

Topic: Molecular IonSection: 9.14Difficulty Level: Easy

143. In electron impact mass spectrometry, a beam of high-energy electrons initially dislodges one electron from the compound being studied. This produces a positively charged ion called the ____________________.Ans: molecular ion

Topic: Relative Abundance Section: 9.17Difficulty Level: Easy

144. What can be determined from the relative abundance of the M +1 peak?

Ans: An approximation for the number of carbon atoms in the molecule.

Topic: Relative Abundance Section: 9.17Difficulty Level: Easy

145. What can be determined from the relative abundance of the M +2 peak?

Ans: The presence of a number of different elements, including S, Br, and Cl.

Topic: Nitrogen Rule Section: 9.17BDifficulty Level: Medium

146. What is the nitrogen rule?Ans: If the molecular ion peak is even, the molecule must contain an even number of

nitrogen atoms (zero is an even number). If the molecular ion peak is odd, the molecule must contain an odd number of nitrogen atoms.)

638

1121792871 organic chemistry 1

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