Organic Chemistry 8th Edition By L. G. Wade Test Bank

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Organic Chemistry 8th Edition By L. G. Wade Test Bank

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Organic Chemistry 8th Edition By L. G. Wade Test Bank

Organic Chemistry, 8e (Wade)

Chapter 5   Stereochemistry

 

1) ________ are isomers which have the same bonding sequence but differ in the orientation of their atoms in space.

Answer:  Stereoisomers

Diff: 1

Section:  5.1

 

2) What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,3-dimethylcyclopentane?

  1. A) not isomers
  2. B) constitutional isomers
  3. C) enantiomers
  4. D) diastereomers
  5. E) conformers

Answer:  B

Diff: 2

Section:  5.1

 

3) What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,5R)-2,3,5-trichloroheptane?

  1. A) not isomers
  2. B) constitutional isomers
  3. C) enantiomers
  4. D) diastereomers
  5. E) conformers

Answer:  B

Diff: 2

Section:  5.1

4) What is the structural relationship between the two molecule shown below?

 

  1. A) constitutional isomers
  2. B) enantiomers
  3. C) diastereomers
  4. D) conformational isomers
  5. E) not isomers

Answer:  A

Diff: 2

Section:  5.1

 

5) How many enantiomers are there of the molecule shown below?

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 6

Answer:  B

Diff: 1

Section:  5.2

6) Which of the following incorrectly describes cis-1,2-dimethylcyclopentane?

  1. A) It is a meso compound.
  2. B) It is achiral.
  3. C) It contains two asymmetric carbons.
  4. D) Its diastereomer is trans-1,2-dimethylcyclopentane.
  5. E) It has an enantiomer.

Answer:  E

Diff: 1

Section:  5.2

 

7) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  the same compound

Diff: 1

Section:  5.2

 

 

8) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  the same compound

Diff: 1

Section:  5.2

 

9) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  enantiomers

Diff: 1

Section:  5.2

10) Is the molecule shown below chiral or achiral?

 

(CH3)3CCH(CH3)2

Answer:  achiral

Diff: 1

Section:  5.2

 

11) How many asymmetric carbon atoms are present in the following compound?

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  B

Diff: 1

Section:  5.2

 

 

12) How many asymmetric carbon atoms are present in the following compound?

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  A

Diff: 1

Section:  5.2

13) How many asymmetric carbons are present in the compound below?

 

Answer:  1

Diff: 1

Section:  5.2

 

14) How many asymmetric carbons are present in the compound below?

 

Answer:  none

Diff: 1

Section:  5.2

 

15) How many asymmetric carbons are present in the compound below?

 

Answer:  5

Diff: 1

Section:  5.2

 

16) How many asymmetric carbon atoms are present in the molecule shown?

 

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  A

Diff: 1

Section:  5.2

17) How many asymmetric carbon atoms are present in the molecule shown?

 

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  A

Diff: 1

Section:  5.2

 

18) How many asymmetric carbon atoms are present in the molecule shown?

 

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  B

Diff: 1

Section:  5.2

 

 

19) How many asymmetric carbon atoms are present in the molecule shown?

 

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  C

Diff: 1

Section:  5.2

20) What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2S,3S,4R)-2,3,4-trichloroheptane?

  1. A) not isomers
  2. B) constitutional isomers
  3. C) enantiomers
  4. D) diastereomers
  5. E) conformers

Answer:  C

Diff: 2

Section:  5.2

 

21) If possible, draw the structure of the enantiomer of the molecule shown below.

 

Answer:

Diff: 2

Section:  5.2

 

 

22) Is the mirror image of the following molecule an enantiomer or is it superimposable with it?

 

Answer:  Superimposable.  The molecule is achiral.

Diff: 2

Section:  5.2

23) Draw the enantiomer of the molecule shown below.

 

Answer:

Diff: 2

Section:  5.2

 

24) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  enantiomers

Diff: 2

Section:  5.2

 

 

25) Which of the statements below correctly describes an achiral molecule?

  1. A) The molecule has a nonsuperimposable mirror image.
  2. B) The molecule exhibits optical activity when it interacts with plane-polarized light.
  3. C) The molecule has an enantiomer.
  4. D) The molecule might be a meso form.
  5. E) None of the above

Answer:  D

Diff: 2

Section:  5.2

26) Circle each chiral molecule among those shown below.

 

 

 

Answer:

Diff: 2

Section:  5.2

 

27) Circle each chiral molecule among those shown below.

 

 

 

Answer:

Diff: 2

Section:  5.2

 

 

28) Is the molecule shown below chiral or achiral?

 

CH3CH2CH(CH3)CH2CH3

Answer:  achiral

Diff: 2

Section:  5.2

29) Is the molecule shown below chiral or achiral?

 

Answer:  achiral

Diff: 2

Section:  5.2

 

30) Is the molecule shown below chiral or achiral?

 

Answer:  chiral

Diff: 2

Section:  5.2

 

31) Is the molecule shown below chiral or achiral?

 

Answer:  achiral

Diff: 2

Section:  5.2

 

32) Is the molecule shown below chiral or achiral?

 

Answer:  achiral

Diff: 2

Section:  5.2

 

33) Is the molecule shown below chiral or achiral?

 

Answer:  chiral

Diff: 2

Section:  5.2

 

34) How many asymmetric carbons are present in the compound below?

 

Answer:  2

Diff: 2

Section:  5.2

 

35) How many asymmetric carbons are present in the compound below?

 

3-ethyl-2,2,4-trimethylpentane

Answer:  1

Diff: 2

Section:  5.2

 

36) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  enantiomers

Diff: 3

Section:  5.2

 

37) Circle all structures shown below that are chiral.

 

 

 

Answer:

Diff: 3

Section:  5.2

 

38) Is the molecule shown below chiral or achiral?

 

Answer:  achiral

Diff: 3

Section:  5.2

 

39) Is the molecule shown below chiral or achiral?

 

Answer:  achiral

Diff: 3

Section:  5.2

 

40) Is the molecule shown below chiral or achiral?

 

Answer:  achiral

Diff: 3

Section:  5.2

 

41) Which of the following structures are achiral and meso?

 

 

  1. A) 1, 2, 3 & 4
  2. B) 1 &2
  3. C) 2 & 3
  4. D) 1 & 4

Answer:  D

Diff: 3

Section:  5.2

 

42) Does the molecule shown below contain asymmetric carbon atoms? Is this molecule chiral?

 

Answer:  Yes, the molecule contains 4 asymmetric carbon atoms. No, the molecule is not chiral since it is superimposable with its mirror image.

Diff: 3

Section:  5.2

 

43) How many asymmetric carbons are present in the compound below?

 

Answer:  5

Diff: 3

Section:  5.2

 

44) Label each asymmetric carbon in the compound below as R or S.

 

Answer:

Diff: 1

Section:  5.3

 

45) Draw the structure of (S)-1-bromo-1-chloropropane. Take particular care to indicate three-dimensional stereochemical detail properly.

Answer:

Diff: 1

Section:  5.3

 

46) Draw the Fischer projection of (S)-2-bromobutane.

Answer:

Diff: 1

Section:  5.3

 

47) Draw the structure of (2R,3R)-2,3-dibromo-3-chloropentane.

Answer:

Diff: 2

Section:  5.3

 

48) Label each asymmetric carbon in the molecule below as having the R or S configuration.

 

 

 

Answer:

Diff: 2

Section:  5.3

 

49) Assign the proper configurational label, R or S, to the chiral carbon in the molecule shown below.

 

Answer:  S

Diff: 2

Section:  5.3

 

50) Assign the proper configurational label, R or S, to each chiral carbon in the molecule below.

 

 

 

Answer:

Diff: 2

Section:  5.3

 

51) Label each asymmetric carbon in the compound below as R or S.

 

Answer:

Diff: 2

Section:  5.3

 

52) Label each asymmetric carbon in the compound below as R or S.

 

Answer:

Diff: 2

Section:  5.3

 

53) Draw the structure of (2R,3S)-2,3-dichloropentane. Take particular care to indicate three-dimensional stereochemical detail properly.

Answer:

Diff: 2

Section:  5.3

 

54) Draw the structure of the enantiomer of (2S, 3R)-2,3-dichloropentane. Take particular care to indicate three-dimensional stereochemical detail properly.

Answer:

Diff: 2

Section:  5.3

 

55) Draw the structure of any diastereomer of (2S, 3R)-2,3-dichloropentane. Take particular care to indicate three-dimensional stereochemical detail properly.

Answer:

Diff: 2

Section:  5.3

 

56) Draw the structure of (1R, 2R)-1-bromo-2-chlorocyclobutane. Take particular care to indicate stereochemistry properly.

Answer:

Diff: 2

Section:  5.3

 

57) Draw the structure of (S)-3-chloro-3-methylhexane. Take particular care to indicate stereochemistry properly.

Answer:

Diff: 2

Section:  5.3

 

58) Draw the structure of (1R, 2S, 3S)-1,2-dibromo-3-ethylcyclohexane. Take particular care to indicate stereochemistry properly.

Answer:

Diff: 2

Section:  5.3

 

59) Label each asymmetric carbon in the compound below as R or S.

 

 

 

 

Answer:

Diff: 2

Section:  5.3

 

60) Label each asymmetric carbon in the compound below as R or S.

 

 

 

Answer:

Diff: 2

Section:  5.3

 

61) Which of the following configurations corresponds to the structure below?

 

  1. A) (4R, 5R)
  2. B) (4R, 5S)
  3. C) (4S, 5R)
  4. D) (4S, 5S)

Answer:  A

Diff: 3

Section:  5.3

 

62) For the structure shown below, draw the stereoisomer having a configuration of (1R,3S,4S) in a perspective structure.

 

 

Answer:

 

Diff: 3

Section:  5.3

 

63) Captopril is used to treat high blood pressure and congestive heart failure.  Label the chiral centers as R or S.

 

Answer:

 

Diff: 3

Section:  5.3

 

64) Label each asymmetric carbon in the compound below as R or S.

 

Answer:

Diff: 3

Section:  5.3

 

65) Label each asymmetric carbon in the compound below as R or S.

 

Answer:

Diff: 3

Section:  5.3

 

66) Phantasmidine, shown below, is found in poisonous frog skin and has analgesic properties (J. Nat. Prod. 2010, 331).  Assign each chiral center as having either R or S configuration.

 

 

 

Answer:

Diff: 3

Section:  5.3

 

67) Compounds that rotate the plane of polarized light clockwise are called ________.

Answer:  dextrorotatory

Diff: 1

Section:  5.4

 

68) Which of the following statements is (are) true for the compound (R)-2-butanol?

  1. A) This compound is chiral.
  2. B) This compound is optically active.
  3. C) This compound has an enantiomer.
  4. D) all of the above
  5. E) none of the above

Answer:  D

Diff: 2

Section:  5.4

 

69) Which of the following statements correctly pertains to a pair of enantiomers?

  1. A) They rotate the plane of polarized light by exactly the same amount and in opposite directions.
  2. B) They rotate the plane of polarized light by differing amounts and in opposite directions.
  3. C) They rotate the plane of polarized light by differing amounts and in the same direction.
  4. D) The have different melting points.
  5. E) They have the same melting point, but they have different boiling points.

Answer:  A

Diff: 2

Section:  5.4

70) If (S)-glyceraldehyde has a specific rotation of -8.7, what is the specific rotation of (R)-glyceraldehyde?

  1. A) 0.0
  2. B) -8.7
  3. C) +8.7
  4. D) cannot be determined from the information given

Answer:  C

Diff: 2

Section:  5.4

 

71) Predict the specific rotation of the compound shown.

 

  1. A) It is impossible to predict; it must be determined experimentally.
  2. B) Because both asymmetric centers are R, the compound is dextrorotatory.
  3. C) Because both asymmetric centers are S, the compound is levorotatory.
  4. D) Zero; the compound is achiral.
  5. E) Because this compound represents a racemic mixture, the compound is dextrorotatory.

Answer:  D

Diff: 2

Section:  5.4

 

72) Would a 50:50 mixture of (2R,3R)-2,3-dibromobutane and (2R,3S)-2,3-dibromobutane be optically active?  Explain.

Answer:  Yes, the mixture would be optically active.  This is not a racemic mixture but a mixture of diastereomers.  The specific rotations of diastereomers are not the same in magnitude nor necessarily opposite in sign.

Diff: 2

Section:  5.4

 

73) Can one predict whether a compound with a single asymmetric carbon is dextro- or levorotatory based on the R/S assignment at this asymmetric carbon? Explain briefly.

Answer:  No. R/S assignment is purely a convention of nomenclature and is completely independent of the direction in which plane-polarized light is rotated by the compound.

Diff: 2

Section:  5.4

74) Given that glucose has a specific rotation of +52.8.  Predict the concentration of a glucose aqueous solution contained in a 10 cm long polarimetry tube if a rotation of +15.8 was observed.

  1. A) 0.299 g/mL
  2. B) .0299 g/mL
  3. C) 3.34 g/mL
  4. D) .334 g/mL

Answer:  A

Diff: 2

Section:  5.4

 

 

75) A student measured the optical activity of an unknown sugar at two different concentrations.  The results of his measurements are shown below.  Given that the sample cell had a path length of 10.0 cm, calculate the specific rotation for the unknown sugar. (Hint: Consider each measurement of plane polarized light has a true reading and a ghost reading 180 from the true reading).

 

concentration    observed rotation

2.00 g sugar in 10.0 mL water      +159.1

5.00 g sugar in 10.0 mL water      +127.8

 

  1. A) -10.5
  2. B) +25.6
  3. C) +79.5
  4. D) -105
  5. E) +256

Answer:  D

Diff: 3

Section:  5.4

 

76) A newly isolated natural product was shown to be optically active. If a solution of 2.0 g in 10 mL of ethanol in a 50 cm tube gives a rotation of +2.57, what is the specific rotation of this natural product?

Answer:  +2.57

Diff: 3

Section:  5.4

77) A mixture of equal amounts of two enantiomers ________.

  1. A) is called a racemic mixture
  2. B) is optically inactive
  3. C) implies that the enantiomers are meso forms
  4. D) both A and B
  5. E) none of the above

Answer:  D

Diff: 2

Section:  5.6

 

78) If a mixture contains 75% of one compound and 25% of its enantiomer, what is the e.e. of the mixture?

  1. A) 100
  2. B) 75
  3. C) 50
  4. D) 25
  5. E) 3

Answer:  C

Diff: 2

Section:  5.7

 

 

79) Calculate the e.e. of a mixture containing 8.0 g of (-)-glyceraldehyde and 2.0 g of (+)-glyceraldehyde.

Answer:  60%

Diff: 2

Section:  5.7

 

80) A mixture of two enantiomers with a composition of 65.0% R has an observed rotation of -25.3 in a  polarimeter tube.  If the mixture has a concentration of 2.038 g/mL at 25C, what is the predicted []25D of an optically pure sample of the S enantiomer?

  1. A) -25.3
  2. B) -53.5
  3. C) +12.4
  4. D) +41.3
  5. E) +53.5

Answer:  D

Diff: 3

Section:  5.7

 

81) The specific rotation of pure (-)-2-butanol is -13.5. What % of a mixture of the two enantiomeric forms is the (+)-form if the specific rotation of this mixture is +7.0?

Answer:  76%

Diff: 3

Section:  5.7

82) (-)-Lactic acid has a specific rotation of -3.8. What is the specific rotation of a solution containing 7.5 g of (-)-lactic acid and 2.5 g of (+)-lactic acid?

Answer:  -1.9

Diff: 3

Section:  5.7

 

83) Explain the stereochemical relationship, if any, among the following two structures and describe whether or not they could be theoretically isolated from each other. (Note: Some H atoms are omitted for clarity.)

 

 

Answer:  These structures are conformationally dependent diastereomers.  They could not be isolated because they are actually the same molecule.

Diff: 3

Section:  5.8

 

 

84) Can a molecule be chiral if it contains no asymmetric carbons? Explain briefly.

Answer:  Yes. The presence of asymmetric carbons is not required for a molecule to be chiral. The only requirement is that the molecule be nonsuperimposable with its mirror image. Structural features other than asymmetric carbons can lead to chirality.

Diff: 2

Section:  5.9

 

85) Is the molecule shown below chiral or achiral?  Explain what this means.

 

 

Answer:  The molecule is chiral because its mirror image is nonsuperimposable.

Diff: 2

Section:  5.9

86) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  enantiomers

Diff: 3

Section:  5.9

 

87) Why is the following structure not a meso compound?

 

 

Answer:  The functional group at the top (aldehyde) is different from the bottom (alcohol) and thus there is no internal reflective plane in the molecule

Diff: 1

Section:  5.10

 

 

88) Draw the Fischer projection of (S)-2-hydroxybutanoic acid, CH3CH2CH(OH)COOH.

Answer:

Diff: 1

Section:  5.10

89) Draw the Fischer projection of (2R,4R)-2,4-dibromopentane.

Answer:

Diff: 2

Section:  5.10

 

90) Translate the structure below to a Fischer projection.

 

 

Answer:

 

Diff: 3

Section:  5.10

 

 

91) Provide a Fischer projection of (2R,3R,4S)-2,3,4-trichloroheptane.

Answer:

Diff: 3

Section:  5.10

92) Provide a Fischer projection of (2S,3S,4S)-2,3,4-trichloroheptane.

Answer:

Diff: 3

Section:  5.10

 

93) How many diastereomers are there of the molecule shown below?

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 6

Answer:  C

Diff: 1

Section:  5.11

 

94) Stereoisomers which are not mirror image isomers are ________.

Answer:  diastereomers

Diff: 1

Section:  5.11

95) Which of the following terms best describes the stereochemical relationship of the two compounds shown below in Fischer notation?

 

  1. A) enantiomers
  2. B) diastereomers
  3. C) constitutional isomers
  4. D) cis/trans isomers
  5. E) meso same structure

Answer:  B

Diff: 2

Section:  5.11

 

96) Which of the following terms correctly describe(s) the structural relationship between cis-1,3-dimethylcyclopentane and trans-1,3-dimethylcyclopentane?

  1. A) enantiomers
  2. B) diastereomers
  3. C) geometric isomers
  4. D) both A and C
  5. E) both B and C

Answer:  E

Diff: 2

Section:  5.11

 

97) What term describes the structural relationship between (E)- and (Z)-2-pentene?

  1. A) not isomers
  2. B) constitutional isomers
  3. C) enantiomers
  4. D) diastereomers
  5. E) conformers

Answer:  D

Diff: 2

Section:  5.11

 

98) What term describes the structural relationship between cis-1,2-dimethylcyclopentane and trans-1,2-dimethylcyclopentane?

  1. A) not isomers
  2. B) constitutional isomers
  3. C) enantiomers
  4. D) diastereomers
  5. E) conformers

Answer:  D

Diff: 2

Section:  5.11

 

99) If possible, draw the structure of any diastereomer of the molecule shown below.

 

Answer:

Diff: 2

Section:  5.11

 

100) If possible, draw the structure of any diastereomer of the molecule shown below.

 

Answer:

Diff: 2

Section:  5.11

 

101) Draw any diastereomer of the molecule shown below.

 

Answer:

Diff: 2

Section:  5.11

 

102) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  diastereomers

Diff: 2

Section:  5.11

 

103) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  the same compound

Diff: 2

Section:  5.11

 

104) One of the stereoisomers of the following oblongolide structure is a natural product isolated from a fungus and has been found to contain antiviral and cytotoxic activities (J. Nat. Prod. 2010, 55). How many stereoisomers exist for this structure?

 

 

  1. A) 6
  2. B) 12
  3. C) 32
  4. D) 64

Answer:  D

Diff: 2

Section:  5.11

 

105) Which of the following statements is (are) true for the compound (3R, 4R)-3,4-dimethylhexane?

  1. A) This compound is chiral.
  2. B) The enantiomer of this compound is (3S, 4S)-3,4-dimethylhexane.
  3. C) This compound is a diastereomer of (3R, 4S)-3,4-dimethylhexane.
  4. D) all of the above
  5. E) none of the above

Answer:  D

Diff: 2

Section:  5.11

 

106) What term describes the structural relationship between (2R,3R,4S)-2,3,4-trichloroheptane and (2R,3R,4R)-2,3,4-trichloroheptane?

  1. A) not isomers
  2. B) constitutional isomers
  3. C) enantiomers
  4. D) diastereomers
  5. E) conformers

Answer:  D

Diff: 2

Section:  5.11

 

107) How many diastereomers are there of the molecule shown below?

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 6

Answer:  E

Diff: 3

Section:  5.11

 

Use the following three structures to answer the questions below.

 

 

 

108) The relationship between I and III is: ________.

  1. A) same compound
  2. B) enantiomers
  3. C) diastereomers
  4. D) constitutional isomers

Answer:  C

Diff: 3

Section:  5.11

 

109) The relationship between I and II is: ________.

  1. A) same compound
  2. B) enantiomers
  3. C) diastereomers
  4. D) constitutional isomers

Answer:  C

Diff: 3

Section:  5.11

 

110) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  diastereomers

Diff: 3

Section:  5.11

 

111) Which of the following terms best describes the pair of compounds shown: enantiomers, diastereomers, or the same compound?

 

Answer:  the same compound

Diff: 3

Section:  5.11

 

112) Which of the following molecules, if isolated in its pure form, would demonstrate optical activity ?

 

 

  1. A) both IV and V
  2. B) both I and III
  3. C) only II
  4. D) both III and IV
  5. E) both I and V

Answer:  A

Diff: 3

Section:  5.12

 

113) Can the molecule shown below be properly described as a meso compound?

 

Answer:  Yes

Diff: 1

Section:  5.13

 

114) Can the molecule shown below be properly described as a meso compound?

 

Answer:  Yes

Diff: 1

Section:  5.13

 

115) How many enantiomers are there of the molecule shown below?

 

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 6

Answer:  A

Diff: 2

Section:  5.13

 

116) If possible, draw the structure of the enantiomer of the molecule shown below.

 

Answer:  The compound is an achiral, meso compound; it has no enantiomer.

Diff: 2

Section:  5.13

 

117) If possible, draw the enantiomer of the molecule shown below.

 

 

Answer:  This molecule is achiral.  It does not have an enantiomer.

Diff: 2

Section:  5.13

 

118) Which of the following statements is (are) true for the compound cis-1,2-dichlorocyclopropane?

  1. A) This compound is chiral.
  2. B) The enantiomer of this compound is trans-1,2-dichlorocyclopropane.
  3. C) This compound contains no asymmetric carbons.
  4. D) all of the above
  5. E) none of the above

Answer:  E

Diff: 2

Section:  5.13

 

119) Draw the structure of the meso form of 1,3-dichlorocyclopentane. Take particular care to indicate three-dimensional stereochemical detail properly.

Answer:

Diff: 2

Section:  5.13

 

120) Can the molecule shown below be properly described as a meso compound?

 

(CH3)2CHCH2CH3

Answer:  No

Diff: 2

Section:  5.13

 

121) Can the molecule shown below be properly described as a meso compound?

 

Answer:  No

Diff: 2

Section:  5.13

 

122) Can the molecule shown below be properly described as a meso compound?

 

Answer:  No

Diff: 2

Section:  5.13

 

123) Which of the structures above are meso structures?

  1. A) I
  2. B) II
  3. C) III
  4. D) II & III
  5. E) None of the previous

Answer:  A

Diff: 3

Section:  5.13

 

124) If possible, draw the enantiomer of the molecule shown below.

 

Answer:  This molecule is achiral.  It does not have an enantiomer.

Diff: 3

Section:  5.13

 

125) Is it theoretically possible to separate the pair of compounds below by distillation? Explain briefly.

 

Answer:  Yes. The molecules are related as diastereomers and hence have different boiling points.

Diff: 2

Section:  5.15

 

126) The process by which enantiomers are separated is called ________.

Answer:  resolution

Diff: 1

Section:  5.16

 

127) Briefly describe how two enantiomers might be separated.

Answer:  The two compounds can be converted to diastereomers, separated based on different physical properties of these diastereomers, and subsequently returned to their original forms after separation. Another method involves the chromatographic separation using a chiral stationary phase.

Diff: 2

Section:  5.16

 

128) Can one separate a mixture of enantiomers by gas chromatography?  Explain.

Answer:  Provided the compounds can be volatilized, a mixture of enantiomers can be separated by GC if an appropriate chiral column can be found.  Enantiomers will be retained differently by the chiral stationary phase of the column.

Diff: 3

Section:  5.16

 

 

Organic Chemistry, 8e (Wade)

Chapter 15   Conjugated Systems, Orbital Symmetry, and Ultraviolet Spectroscopy

 

1) What is the hybridization of the central carbon of allene (1,2-propadiene)?

  1. A) sp
  2. B) sp2
  3. C) sp3
  4. D) p
  5. E) none of the above

Answer:  A

Diff: 1

Section:  15.2

 

2) What descriptive term is applied to the type of diene represented by 2,4-hexadiene?

  1. A) conjugated diene
  2. B) cumulated diene
  3. C) isolated diene
  4. D) alkynyl diene
  5. E) none of the above

Answer:  A

Diff: 1

Section:  15.2

 

3) What descriptive term is applied to the type of diene represented by 1,5-octadiene?

  1. A) conjugated diene
  2. B) cumulated diene
  3. C) isolated diene
  4. D) alkynyl diene
  5. E) none of the above

Answer:  C

Diff: 1

Section:  15.2

 

4) What descriptive term is applied to the type of diene shown?

 

 

  1. A) conjugated diene
  2. B) cumulated diene
  3. C) isolated diene
  4. D) alkynyl diene
  5. E) none of the above

Answer:  C

Diff: 1

Section:  15.2

 

5) Which of the following molecules is chiral?

  1. A) 1,2-pentadiene
  2. B) 2,3-pentadiene
  3. C) 2-methyl-2,3-pentadiene
  4. D) 2-chloro-4-methyl-2,3-pentadiene
  5. E) None of the above molecules is chiral.

Answer:  B

Diff: 2

Section:  15.2

 

6) Which of the following compounds has the most negative heat of hydrogenation?

  1. A) 1,4-hexadiene
  2. B) 1,5-hexadiene
  3. C) 1,2-hexadiene
  4. D) 1,3-hexadiene
  5. E) hex-1-ene

Answer:  C

Diff: 2

Section:  15.2

 

7) Which compound has the smallest heat of hydrogenation?

  1. A) 5-methyl-1,2-hexadiene
  2. B) (E)-5-methyl-1,3-hexadiene
  3. C) 5-methyl-1,4-hexadiene
  4. D) 2-methyl-1,5-hexadiene
  5. E) (E)-2-methyl-2,4-hexadiene

Answer:  E

Diff: 2

Section:  15.2

 

8) Rank the following dienes in order of increasing stability: trans-1,3-pentadiene, cis-1,3-pentadiene, 1,4-pentadiene, and 1,2-pentadiene.

Answer:  1,2-pentadiene < 1,4-pentadiene < cis-1,3-pentadiene < trans-1,3-pentadiene

Diff: 2

Section:  15.2

 

9) Among a series of isomeric trienes, the more negative the H of the hydrogenation reaction of a given triene, the ________ stable it is relative to the others in the isomeric series.

Answer:  less

Diff: 2

Section:  15.2

 

10) Which of the following compounds is the most stable?

  1. A) (E)-2-methyl-1,3-pentadiene
  2. B) 2-methyl-1,2-pentadiene
  3. C) (Z)-2-methyl-1,3-pentadiene
  4. D) 2-methyl-2,3-pentadiene
  5. E) 2-methyl-1,4-pentadiene

Answer:  A

Diff: 2

Section:  15.2

 

11) Consider the hydrogenation of each compound listed and rank the compounds in order of increasing H. The most negative H should be listed first.

 

cis-pent-2-ene, 2,3-pentadiene, and trans-1,3-pentadiene

Answer:  2,3-pentadiene < trans-1,3-pentadiene < cis-pent-2-ene

Diff: 3

Section:  15.2

 

12) Consider the hydrogenation reaction of each compound listed and rank the compounds in order of increasing H of this reaction. The most negative H should be listed first.

 

2,5-dimethyl-1,3-cycloheptadiene,

1,4-dimethyl-1,3-cycloheptadiene, and

3,6-dimethyl-1,4-cycloheptadiene

 

Answer:  3,6-dimethyl-1,4-cycloheptadiene

< 2,5-dimethyl-1,3-cycloheptadiene

< 1,4-dimethyl-1,3-cycloheptadiene

Diff: 3

Section:  15.2

 

13) When the relative energies of the s-cis and s-trans conformers of 1,3-butadiene are compared, one finds that:

  1. A) the s-cis conformer is lower in energy than the s-trans.
  2. B) the s-trans conformer is lower in energy than the s-cis.
  3. C) the two conformers are of equal energy.

Answer:  B

Diff: 1

Section:  15.3

 

14) In the planar conformation of 1,3-butadiene, the electron density in the -system is ________ over the entire molecule.

Answer:  delocalized

Diff: 1

Section:  15.3

 

15) Show how the carbon p orbitals overlap to form the lowest energy molecular orbital of 1,3-butadiene.

Answer:

Diff: 1

Section:  15.3

 

16) Draw (E)-1,3-hexadiene in its s-cis conformation.

Answer:

Diff: 2

Section:  15.3

 

17) Draw the most stable conformation of (2Z,4E)-2,4-hexadiene.

Answer:

Diff: 2

Section:  15.3

 

18) Draw (Z)-1,3-hexadiene in its s-trans conformation.

Answer:

Diff: 2

Section:  15.3

 

19) How many nodes, other than the node coincident with the molecular plane, are found in the highest energy MO of 1,3-butadiene?

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) none of the above

Answer:  D

Diff: 2

Section:  15.3

 

20) What is the resonance energy of a system?

Answer:  The extra stability which arises when conjugation is present in a molecule.

Diff: 2

Section:  15.3

 

21) Give a representation of the highest occupied MO of 1,3-butadiene in its ground state.

Answer:

Diff: 2

Section:  15.3

 

22) Give a representation of the lowest occupied MO of 1,3-butadiene in its ground state.

Answer:

Diff: 2

Section:  15.3

 

23) Draw the LUMO of 1,3-butadiene.

Answer:

 

Diff: 2

Section:  15.3

 

24) Draw the HOMO of 1,3-butadiene.

Answer:

 

Diff: 2

Section:  15.3

 

25) How many molecular orbitals are needed to represent the conjugated pi system of -carotene?

 

  1. A) 1
  2. B) 10
  3. C) 11
  4. D) 20
  5. E) 22

Answer:  E

Diff: 3

Section:  15.3

 

26) Which of the following represents the highest occupied molecular orbital for the conjugated pi system in Vitamin D3?

 

 

  1. A)
  2. B)
  3. C)
  4. D)

Answer:  A

Diff: 3

Section:  15.3

 

27) When (S)-3-bromopent-1-ene is heated in water, which of the following compounds is not produced?

  1. A) (S)-pent-1-en-3-ol
  2. B) (R)-pent-1-en-3-ol
  3. C) pent-4-en-1-ol
  4. D) (E)-pent-2-en-1-ol
  5. E) (Z)-pent-2-en-1-ol

Answer:  C

Diff: 2

Section:  15.4

 

28) Which of the following alkyl halides yields the most stable carbocation intermediate during solvolysis in hot ethanol?

  1. A) methyl iodide
  2. B) (S)-2-bromopentane
  3. C) (R)-2-bromopentane
  4. D) (S)-3-bromopent-1-ene
  5. E) 1-chlorobutane

Answer:  D

Diff: 2

Section:  15.4

29) When 3-bromobut-1-ene is heated in a good ionizing solvent, reactions occur through a carbocation intermediate. Draw all reasonable resonance contributors of this cation and indicate which is the major contributor.

Answer:

Diff: 2

Section:  15.4

 

30) Provide a detailed, stepwise mechanism for the reaction shown below.

 

Answer:

Diff: 2

Section:  15.4

 

31) When 3-bromo-1-methylcyclohexene is heated in a good ionizing solvent, reactions occur through a carbocation intermediate. Draw all reasonable resonance contributors of this cation and indicate which is the major contributor.

Answer:

Diff: 3

Section:  15.4

 

32) When 1-methylcyclohex-2-en-1-ol is treated with HBr, two constitutionally isomeric bromides are produced. Provide a detailed, stepwise mechanism which explains this observation.

Answer:

Diff: 3

Section:  15.4

 

33) Name the two major products which are formed when 3-bromo-1-methylcyclohexene undergoes solvolysis in hot methanol.

Answer:  3-methoxy-1-methylcyclohexene and 3-methoxy-3-methylcyclohexene

Diff: 3

Section:  15.4

 

34) Provide the structure of the major product which results from 1,4-addition of Br2 to the diene shown below.

 

Answer:

Diff: 1

Section:  15.5

 

35) Provide the two major organic products of the following reaction.

 

Answer:

Diff: 2

Section:  15.5

 

36) Provide the two major organic products of the following reaction.

 

Answer:

Diff: 2

Section:  15.5

 

37) Provide the structure of the major product which results from 1,2-addition of HBr to the diene shown below.

 

Answer:

Diff: 2

Section:  15.5

 

38) When 1 mole of anhydrous HCl is reacted with excess 1,3-pentadiene, both the 1,2 and the 1,4-addition products are formed.  Which of the following structures shown below is the least likely to be one of these products? (Note: When a chiral carbon is formed in this reaction a racemic mixture results, only one of the two possible enantiomers is shown.)

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

Answer:  D

Diff: 3

Section:  15.5

 

39) Draw structures for the two major products of the following reaction.

 

 

Answer:

 

 

Diff: 3

Section:  15.5

 

40) In the addition of HBr to conjugated dienes, is the product which results from 1,2-addition or that which results from 1,4-addition typically the product of kinetic control?

Answer:  The product of kinetic control typically results from 1,2-addition.

Diff: 1

Section:  15.6

 

41) What name is given to the type of control which arises in a reaction which does not achieve equilibrium and in which the product distribution is determined by the relative activation energies of the pathways which produced them?

Answer:  kinetic control

Diff: 1

Section:  15.6

 

42) Draw the structure of the major product which results when the diene shown is treated with HBr at 40C.

 

Answer:

Diff: 2

Section:  15.6

 

43) Draw the structure of the major product which results when the diene shown is treated with HBr at -80C.

 

Answer:

Diff: 2

Section:  15.6

 

44) Draw the resonance structures of the intermediate and then predict the two major products in the following reaction and label them as a kinetic or thermodynamic product.

 

 

 

 

Answer:  Resonance Structures of Carbocation intermediate

 

Predicted Products

Diff: 3

Section:  15.6

 

45) What is the major organic product which results when cycloheptene is irradiated in the presence of N-bromosuccinimide?

  1. A) 1-bromocycloheptene
  2. B) 2-bromocycloheptene
  3. C) 1,2-dibromocycloheptane
  4. D) 3-bromocycloheptene
  5. E) 4-bromocycloheptene

Answer:  D

Diff: 1

Section:  15.7

 

46) Into what is NBS converted as it reacts in allylic bromination reactions?

Answer:  succinimide

Diff: 2

Section:  15.7

 

47) Including all possible stereoisomeric forms, how many distinct allylic bromides could be produced when 2-methylpent-1-ene is treated with NBS under irradiation by a sunlamp?

  1. A) 2
  2. B) 3
  3. C) 4
  4. D) 5
  5. E) 6

Answer:  D

Diff: 3

Section:  15.7

 

48) Three halogenated organic products result from the reaction below.  Draw the structure of each product and then circle the most stable product.

 

Answer:

Diff: 3

Section:  15.7

 

49) Draw the resonance structures of the intermediate and then predict the two major products in the following reaction.

 

 

 

Answer:  Resonance structures of Intermediate

 

Predicted Products

Diff: 3

Section:  15.7

 

50) Provide the necessary synthetic sequence for preparing 1,3-cyclopentadiene from cyclopentane.

Answer:

  1. Br2, h
  2. KOH
  3. NBS, h
  4. KOH

Diff: 3

Section:  15.7

 

51) Give a representation of the bonding molecular orbital of the allyl anion.

Answer:

Diff: 2

Section:  15.8

52) Show how the carbon p orbitals overlap to form the 2 molecular orbital of the allyl cation.

Answer:

Diff: 2

Section:  15.8

 

53) Show how the carbon p orbitals overlap to form the LUMO of the allyl anion.

Answer:

Diff: 2

Section:  15.8

 

54) Draw the HOMO of allyl anion.

Answer:

Diff: 2

Section:  15.8

 

55) Draw the HOMO of pentadienyl cation.

Answer:

Diff: 2

Section:  15.8

 

56) Draw the HOMO of pentadienyl anion.

Answer:

Diff: 2

Section:  15.8

57) Give a representation of the antibonding molecular orbital of the allyl cation.

Answer:

Diff: 2

Section:  15.8

 

 

58) Draw the LUMO of pentadienyl cation.

Answer:

Diff: 3

Section:  15.8

 

59) Draw the LUMO of pentadienyl anion.

Answer:

 

Diff: 3

Section:  15.8

 

60) In the allyl radical, which molecular orbital is singly occupied?

  1. A) The bonding molecular orbital.
  2. B) The nonbonding molecular orbital.
  3. C) The antibonding molecular orbital.
  4. D) None of the above.

Answer:  B

Diff: 2

Section:  15.9

 

61) How many electrons are present in the nonbonding molecular orbital of the allyl cation?

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  A

Diff: 2

Section:  15.9

62) How many electrons are present in the nonbonding molecular orbital of the allyl cation?

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  A

Diff: 2

Section:  15.9

 

 

63) How many electrons populate the molecular orbitals of the allyl radical?

  1. A) 0
  2. B) 1
  3. C) 2
  4. D) 3
  5. E) 4

Answer:  D

Diff: 2

Section:  15.9

 

64) Which substrate would react most rapidly in an SN2 reaction?

  1. A) CH3CH2CH=CHCH2Br
  2. B) BrCH2CH2CH=CHCH3
  3. C) CH3CHBrCH=CH2CH3
  4. D) CH3CH2CH2CH=CHBr

Answer:  A

Diff: 2

Section:  15.10

 

65) What reagent could be used to convert allyl tosylate directly into oct-1-ene?

Answer:  n-pentyllithium  or  n-pentylmagnesium bromide

Diff: 2

Section:  15.10

 

66) Explain why SN2 reactions on allyl bromide proceed faster than corresponding reactions on ethyl bromide.

Answer:  When the substrate is allylic, resonance stabilization through conjugation with the adjacent bond occurs in the transition state. This delocalization lowers the energy of the transition state and results in an enhanced rate.

Diff: 3

Section:  15.10

67) For what does the acronym HOMO stand?

Answer:  highest occupied molecular orbital

Diff: 1

Section:  15.11

 

68) Which of the following terms best describes a Diels-Alder reaction?

  1. A) a [4+2] cycloaddition
  2. B) a [2+2] cycloaddition
  3. C) a sigmatropic rearrangement
  4. D) a 1,3-dipolar cycloaddition
  5. E) a substitution reaction

Answer:  A

Diff: 1

Section:  15.11

 

69) When 1,3-butadiene reacts with CH2CHCN, which of the terms below best describes the product mixture?

  1. A) a mixture of two diastereomers
  2. B) a single compound
  3. C) a racemic mixture
  4. D) optically active
  5. E) a mixture of bicyclic compounds

Answer:  C

Diff: 1

Section:  15.11

 

70) Provide the structure of the major organic product in the following reaction.

 

Answer:

Diff: 1

Section:  15.11

71) What diene and dienophile would react to give the product below?

 

Answer:

Diff: 1

Section:  15.11

 

 

72) What diene and dienophile would react to give the product below?

 

Answer:

Diff: 1

Section:  15.11

 

73) Draw the s-cis conformation of (E)-1,3-hexadiene.

Answer:

Diff: 2

Section:  15.11

 

74) Draw the s-trans conformation of (Z)-1,3-hexadiene.

Answer:

Diff: 2

Section:  15.11

75) The Diels-Alder reaction is a concerted reaction; this means:

  1. A) a mixture of endo and exo products are formed.
  2. B) all bond making and bond breaking occurs simultaneously.
  3. C) the products contain rings.
  4. D) the reaction follows Markovnikovs rule.
  5. E) the reaction is highly endothermic.

Answer:  B

Diff: 2

Section:  15.11

 

 

76) Which of the following compounds is the most reactive dienophile in a Diels-Alder reaction with 1,3-butadiene?

  1. A) CH2CHOCH3
  2. B) CH2CHCHO
  3. C) CH3CHCHCH3
  4. D) (CH3)2CCH2
  5. E) CH2CH2

Answer:  B

Diff: 2

Section:  15.11

 

77) Provide the structure of the major organic product in the following reaction.

 

Answer:

Diff: 2

Section:  15.11

78) Provide the major organic product of the following reaction.

 

Answer:

Diff: 2

Section:  15.11

 

 

79) Provide the major organic product of the following reaction.

 

Answer:

Diff: 2

Section:  15.11

80) Provide the major organic product of the following reaction.

 

Answer:

Diff: 2

Section:  15.11

 

81) What diene and dienophile are used in the Diels-Alder route to the compound shown?

 

Answer:

Diff: 2

Section:  15.11

 

82) What diene and dienophile are used in the Diels-Alder route to the compound shown?

 

Answer:

Diff: 2

Section:  15.11

83) Provide the structure of the major organic product in the following reaction.

 

Answer:

Diff: 2

Section:  15.11

 

84) Provide the structure of the major organic product in the following reaction.

 

Answer:

Diff: 2

Section:  15.11

 

 

85) What diene and dienophile would react to give the product below?

 

Answer:

Diff: 2

Section:  15.11

86) What diene and dienophile would react to give the product below?

 

Answer:

Diff: 2

Section:  15.11

 

87) What diene and dienophile would react to give the product below?

 

Answer:

Diff: 2

Section:  15.11

 

 

88) Which diene reacts more rapidly in Diels-Alder reactions, cyclopentadiene or 1,3-butadiene? Briefly explain your choice.

Answer:  Cyclopentadiene reacts more rapidly since its -system is fixed in the s-cis conformation.

Diff: 2

Section:  15.11

89) Which sequence correctly ranks the following dienes in order of increasing reactivity

in the Diels-Alder reaction?

 

 

  1. A) 1 < 2 < 3
  2. B) 2 < 3 < 1
  3. C) 3 < 1 < 2
  4. D) 3 < 2 < 1

Answer:  D

Diff: 2

Section:  15.11

 

90) Provide the structure of the major organic product in the following reaction.

 

 

Answer:

Diff: 2

Section:  15.11

 

91) Provide the structure of the major organic product in the following reaction.

 

 

Answer:

Diff: 2

Section:  15.11

 

92) Provide the structure of the major organic product in the following reaction.

 

 

Answer:

Diff: 2

Section:  15.11

 

93) Provide the structure of the major organic product in the following reaction.

 

 

Answer:

Diff: 2

Section:  15.11

 

94) According to the 1,3-butadiene structure below, which positions would be best to place methoxy groups to yield the most reactive dimethoxy-1,3-butadiene isomer in the Diels-Alder reaction?

 

  1. A) c and d
  2. B) a and c
  3. C) b and c
  4. D) a and d
  5. E) a and f

Answer:  D

Diff: 3

Section:  15.11

 

95) Provide the structure of the major organic product in the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

96) Provide the major organic product of the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

97) Provide the major organic product of the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

98) Provide the major organic product of the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

99) Provide the major organic product of the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

100) Provide the major organic product of the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

101) Provide the major organic product of the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

102) Provide the major organic product of the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

103) Assuming kinetic conditions, provide the correct stereochemistry and regiochemistry of the major product of the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

104) Provide the structure of the major organic product in the following reaction.

 

Answer:

Diff: 3

Section:  15.11

 

105) Provide the structure of the major organic product in the following reaction.

 

Answer:

Diff: 3

Section:  15.11

106) What are the structures of A, B, and C?

 

Answer:

Diff: 3

Section:  15.11

 

107) Why does the (E,E)-isomer of 2,4-hexadiene react much more rapidly with dienophiles than does the (Z,Z)-isomer?

Answer:  The s-cis conformation, which is required for participation in a Diels-Alder reaction, is hindered by a severe CH3/CH3 steric interaction in the (Z,Z)-isomer.

Diff: 3

Section:  15.11

 

108) Why does the diene shown below fail to undergo a Diels-Alder reaction with even the most reactive dienophiles?

 

Answer:  The diene cannot achieve the necessary s-cis conformation.

Diff: 3

Section:  15.11

109) Dicylopentadiene results when cyclopentadiene reacts with itself in a Diels-Alder reaction. Provide the structure of dicyclopentadiene. Pay particular attention to stereochemical detail.

Answer:

Diff: 3

Section:  15.11

 

110) The following Diels-Alder reaction was featured in Tet. Lett. 2011, 960.  Predict the structure of the starting materials.

 

 

 

Answer:

 

 

Diff: 3

Section:  15.11

 

 

111) Assuming kinetic conditions, draw the major product of the reaction below.  Include

correct stereochemistry.

 

 

 

Answer:

 

Diff: 3

Section:  15.11

112) Predict the major product of the following reaction:

 

 

Answer:

Diff: 3

Section:  15.11

 

113) What characterizes a pericyclic reaction?

Answer:  Pericyclic reactions involve concerted breaking and formation of bonds within a closed ring of interacting orbitals.

Diff: 2

Section:  15.12

 

 

114) Provide a picture of the HOMO of 1,3,5-hexatriene.

Answer:

Diff: 3

Section:  15.12

 

115) Provide a picture of the LUMO of 1,3,5-hexatriene.

Answer:

Diff: 3

Section:  15.12

116) Predict the outcome of the reaction shown below.

 

Answer:

Diff: 3

Section:  15.12

 

117) Consider the possible thermal [4+4] cycloaddition of two molecules of 1,3-butadiene to generate cycloocta-1,5-diene. Show the HOMO/LUMO interaction which would result, and use this interaction to predict whether the proposed cycloaddition could occur.

Answer:

 

The cycloaddition is thermally forbidden.

Diff: 3

Section:  15.12

 

 

118) Is the thermal [4+2] cycloaddition between allyl anion and ethylene an allowed one? To answer, draw the HOMO of allyl anion and the LUMO of ethylene, and comment on the symmetry match of the two.

Answer:

 

The cycloaddition is thermally allowed.

Diff: 3

Section:  15.12

119) Indicate whether the following cyclization, conducted under thermal conditions, is symmetry allowed. Justify your answer by showing whether the overlapping orbitals in the transition state generate a symmetry-allowed or symmetry-forbidden scenario.  Treat ethylene as the nucleophile.

 

Answer:

Diff: 3

Section:  15.12

 

 

120) The following [3+2] cycloaddition was reported in Organic Letters, 2011, 402.  Predict whether the reaction would be thermally or photochemically promoted.  Justify your answer by showing overlap of the correct molecular orbitals.  Assume the alkene is the electrophile.

 

 

Answer:

 

Diff: 3

Section:  15.12

121) Absorption of UV-visible energy by a molecule results in:

  1. A) vibrational transitions
  2. B) electronic transitions
  3. C) rotational transitions
  4. D) nuclear transitions
  5. E) none of the above

Answer:  B

Diff: 1

Section:  15.13

 

122) Which of the following compounds absorbs the longest wavelength of UV-visible light?

  1. A) (E)-but-2-ene
  2. B) (Z)-but-2-ene
  3. C) hex-1-ene
  4. D) (Z)-1,3-hexadiene
  5. E) (E)-1,3,5-hexatriene

Answer:  E

Diff: 1

Section:  15.13

 

 

123) UV spectroscopy measures the energy required to promote an electron from the ________ molecular orbital to the ________ molecular orbital.

  1. A) highest occupied, lowest unoccupied
  2. B) lowest occupied, lowest unoccupied
  3. C) lowest occupied, highest unoccupied
  4. D) highest occupied, highest unoccupied
  5. E) None of the above

Answer:  A

Diff: 1

Section:  15.13

 

124) Which compound requires a higher energy photon to cause a p to p* (HOMO/LUMO) transition, 1,3-butadiene or 1,3,5-hexatriene?

Answer:  1,3-butadiene

Diff: 1

Section:  15.13

125) How many nodes, other than the node coincident with the molecular plane, are present in the HOMO of 1,3,5-hexatriene?

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

Answer:  B

Diff: 2

Section:  15.13

 

126) How many nodes, other than the node coincident with the molecular plane, are present in the LUMO of 1,3,5-hexatriene?

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

Answer:  C

Diff: 2

Section:  15.13

 

127) In the UV-visible spectrum of (E)-1,3,5-hexatriene, the lowest energy absorption corresponds to a:

  1. A) to transition.
  2. B) to *
  3. C) to *
  4. D) to *
  5. E) to *

Answer:  E

Diff: 2

Section:  15.13

128) Which sequence correctly ranks the following conjugated systems in order of increasing UV 8max absorption values?

 

 

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

Answer:  C

Diff: 2

Section:  15.13

 

129) Which has a lmax in its UV spectrum at a longer wavelength, 2,4-hexadiene, 1,4-he

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