Ch9-ques-2013

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Chapter 9

Multiple Choice Questions:

Topic: Addition Reaction Mechanisms Section: 9.1

Difficulty Level: Easy

1. In an addition reaction to an alkene, the π bond plays the role of: A) nucleophile B) electrophile C) leaving group D) A and B E) B and C Ans: A

Topic: Addition Reaction Mechanisms Section: 9.1

Difficulty Level: Moderate

2. Addition reactions of alkenes are characterized by: A) formation of a π bond

B) addition of two groups across a double bond C) breaking of a π bond

D) A and B E) B and C Ans: E

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Topic: Addition vs. Elimination Thermodynamic Perspective Section: 9.2

3. The decrease in entropy (the ΔS value is negative) observed for alkene addition reactions results from:

A) the breaking of a π and σ bond. B) the formation of two σ bonds. C) the reaction being exothermic.

D) two molecules reacting to form a single molecule. E) the temperature dependence of the ΔS term. Ans: D

4. In a reaction where addition and elimination reactions are in competition, which of the following statements is most correct?

A) Addition and elimination reactions are favored at low temperatures. B) Addition and elimination reactions are favored at high temperatures. C) Only addition reactions are favored at low temperatures.

D) Only elimination reactions are favored at low temperatures.

E) Addition and elimination reactions are disfavored at low temperatures. Ans: C

5. Which statement is true about the temperature dependence of an addition reaction? A) Addition reactions are thermodynamically favorable at all temperatures. B) Addition reactions are thermodynamically disfavored at all temperatures. C) Addition reactions are thermodynamically favorable at low temperatures. D) Addition reactions are thermodynamically favorable at high temperatures. E) Addition reactions are thermodynamically impossible.

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6. For an addition reaction, why does the free energy term, ΔG, become more positive with increasing temperature?

A) The positive entropy term dominates at high temperature. B) The negative entropy term dominates at high temperature. C) The positive enthalpy term dominates at high temperature. D) The negative enthalpy term dominates at high temperature. E) The enthalpy and entropy terms cancel at high temperature. Ans: A

Difficulty Level: Hard

7. Addition reactions are favorable at low temperatures because:

A) the positive enthalpy term is larger than the negative entropy term. B) the negative enthalpy term is larger than the positive entropy term. C) the positive enthalpy term is smaller than the negative entropy term. D) the negative enthalpy term is smaller than the positive entropy term. E) the enthalpy and entropy terms are equal.

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Topic: Hydrohalogenation Section: 9.3

8. Which of the molecules below would be the expected product for hydrohalogenation of the following alkene:

A) B) C) D) Br Br E) Br Ans: E Topic: Hydrohalogenation Section: 9.3

9. In the addition reaction of HI to 2-methyl-2-butene, the Markovnikov addition mechanism involves:

A) attack of 2-methyl-2-butene initiated by an iodide ion. B) attack of 2-methyl-2-butene initiated by an iodine atom. C) isomerization of 2-iodo-2-methylbutene.

D) formation of a carbocation at carbon two (C-2). E) formation of carbocation at carbon three (C-3). Ans: D

10. The expected Markovnikov addition product of HI to 2-methyl-2-butene is: A) 2-iodopentane

B) 2-iodo-2-methylbutane C) 1-iodo-2-methylbutane D) 2-iodo-1-methylbutane E) 3-iodo-2-methylbutane

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Ans: B

11. The regioselectivity and stereospecificity in hydrohalogenation of an alkene is best described as:

A) Markovnikov orientation with syn-addition B) Markovnikov orientation with anti-addition C) anti-Markovnikov orientation with syn-addition D) anti-Markovnikov orientation with anti-addition

E) Markonikov orientation with both syn- and anti-addition Ans: E

12. Which of the structures shown depicts the most stable carbocation intermediate formed in a hydrohalogenation reaction?

CH₂ CH₃ CH₃ CH₃ CH₃ I II III IV V A) I B) II C) III D) IV E) V Ans: B

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13. What compound is the expected product upon Markovnikov hydrohalogenation with HBr of the alkene shown below?

A) Br B) Br C) Br D) Br E) Br Ans: B Topic: Hydrohalogenation Section: 9.3

14. The expected major product of the following reaction is:

HBr ? A) Br B) Br C) Br D) Br E) Br Br Ans: C

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HBr ? ROOR A) Br B) C) Br D) Br E) Br _Br Ans: A Topic: Hydrohalogenation Section: 9.3

16. What is the expected major product for the following reaction?

Br Br Br Br II III IV V I HBr ? ROOR A) I B) II C) III D) IV E) V Ans: D

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Topic: Anti-Markovnikov Hydrohalogenation Section: 9.3

17. Which of the molecules below arises from anti-Markovnikov hydrohalogenation with HBr of the alkene shown?

A) Br B) Br C) Br D) Br E) Br Ans: C

Topic: Stereochemistry of Hydrohalogenation Section: 9.3

18. Which of the alkenes shown below would produce a chirality center upon hydrohalogenation? A) B) C) CH3 D)

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E) Ans: B

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19. What is the major product for the following reaction?

HI A) I B) I C) I D) I I E) I Ans: A

20. Which of the alkenes below would be expected to produce a chirality center upon hydrohalogenation in the presence of peroxide?

A) B) C) D) E) Ans: B

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21. Which of the given reaction schemes would produce the molecule shown below?

Br A) HBr ROOR B) HBr C) HBr ROOR D) Both A and B E) Both B and C Ans: E

22. Which of the molecules below are enantiomers, formed as products upon reaction of HBr with 4-methylpent-1-ene? H Br H Br Br H H Br I II III IV A) I and II B) II and III C) III and IV D) I and III E) II and IV Ans: E

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Topic: Hydrohalogenation and Carbocation Rearrangements Section: 9.3

23. Which of the following carbocations is likely to undergo rearrangement through a methyl shift? H3C H3C I II III H2C CH3 CH3 CH3 A) I B) II C) III D) I and II E) II and III Ans: D

24. Which of the following carbocations is likely to undergo rearrangement through a hydride shift? CH3 I II III CH2 CH2 A) I B) II C) III D) I and II E) II and III Ans: D

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25. The expected major product(s) of HCl addition to the alkene shown would be:

Br I II III Br Cl Br Cl Br Cl Br Cl IV V Br Cl ? HCl A) I and II B) II and III C) I and IV D) V

E) All of the above are equally likely to form Ans: A

26. The expected major product(s) of HBr addition to the alkene shown would be: HBr A) Br B) Br + enantiomer C) Br + enantiomer Br D) Br E) Br Ans: A

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Topic: Stereochemistry of Hydrohalogenation and Carbocation Rearrangements Section: 9.3

27. The reaction shown below would be expected to produce as major products which of the following compounds?

HCl A) Cl + enantiomer B) Cl + enantiomer C) Cl + enantiomer D) Cl + enantiomer E) Cl + enantiomer Ans: D

28. What is the IUPAC name of the expected major product formed upon reaction of HCl with 3-methyl-1-butene? A) 1-Chloro-2-methylbutane B) 1-Chloro-3-methylbutane C) 2-Chloro-2-methylbutane D) 2-Chloro-3-methylbutane E) 1-Chloropentane Ans: C

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29. Select the expected major product(s) of the following reaction:

HBr ? A) Br B) Br C) Br D) A and B E) A and C Ans: C

30. Identify the expected product(s) for the reaction shown below?

HBr A) Br + enantiomer B) Br C) Br + enantiomer D) Br + enantiomer E) Br + enantiomer Ans: C

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Topic: Acid Catalyzed Hydration Section: 9.4

31. The regioselectivity and stereospecificity in the acid-catalyzed hydration of an alkene is best described as:

E) Markonikov orientation with both syn- and anti-addition Ans: E

H+ ? H2O OH OH OH OHOH II III IV V I OH A) I B) II C) III D) IV E) V Ans: D

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OH OH OH OH II III IV V I H3O+ H2O A) I B) II C) III D) IV E) V Ans: C

H3O+ ? A) OH OH B) OH OH C) OH D) OH E) OH

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Ans: D

35. Treatment of 1-methylcyclohexene with H3O+ would be expected to yield as the major product which of the molecules below?

II III IV V I HO HO HO HO _OH A) I and III B) II C) III and V D) IV E) I, III and V Ans: D

36. Treatment of (S)-6-chloro-1-methyl-1-cyclohexene with H3O+ is expected to

produce which of the following?

II III IV V I Cl OH Cl Cl Cl Cl OH OH OH OH A) I and III B) II C) III and V D) IV E) I, III and V Ans: B

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[H2SO4] MeOH A) OMe B) + enantiomer OMe C) + enantiomer OMe D) + enantiomer OMe E) + enantiomer OMe Ans: A

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Topic: Oxymercuration-Demercuration Section: 9.5

38. The regioselectivity and stereospecificity in the oxymercuration-demercuration of an alkene is best described as:

E) Markonikov orientation with both syn- and anti-addition Ans: B

1. Hg(OAc)2, H2O 2. NaBH4, NaOH A) B) + enantiomer OH C) + enantiomer OH HO D) HO E) HO Ans: B

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40. What synthetic goal is achieved by subjecting an alkene to an oxymercuration-demercuration reaction sequence?

A) Markovnikov addition of H2O, promoting skeletal rearrangement

B) Markovnikov addition of H2O, preventing skeletal rearrangement

C) anti-Markovnikov addition of H2O, promoting skeletal rearrangement

D) anti-Markovnikov addition of H2O, preventing skeletal rearrangement

E) anti-Markovnikov addition of H2O, syn-hydroxylation

Ans: B

1. Hg(OAc)2, H2O 2. NaBH4, NaOH A) O H O B) + enantiomer OH C) OH D) + enantiomer OH E) + enantiomer OH OH Ans: C

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1. Hg(OAc)2, H2O 2. NaBH₄, NaOH A) + enantiomer OH B) + enantiomer OH OH C) + enantiomer OH D) + enantiomer HO E) + enantiomer OH Ans: D

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1. Hg(OAc)2, EtOH 2. NaBH4, NaOH A) O B) O C) O D) O HO + CO2 E) OH Ans: B Topic: Oxymercuration-Demercuration Section: 9.5

44. When an alkene is subjected to treatment with Hg(OAc)2 in alcohol, followed by

reaction with NaBH₄, what functional group is formed? A) ether B) epoxide C) alkane D) syn diol E) alkyne Ans: A

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Topic: Hydroboration-Oxidation Section: 9.6

45. The regioselectivity and stereospecificity in the hydroboration-oxidation of an alkene is best described as:

A) Markovnikov orientation with syn-addition B) Markovnikov orientation with anti-addition C) Anti-Markovnikov orientation with syn-addition D) Anti-Markovnikov orientation with anti-addition

E) Markovnikov orientation with both syn- and anti-addition Ans: C

46. What reagents are needed to accomplish the following transformation?

CH3 _? CH3 OH _! A) H2O/H+ B) H2O/Peroxide C) OH– D) BH3 E) 1. BH3, 2. HO–, H2O2, H2O Ans: E

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47. What is the expected major product for the following reaction sequence?

1. BH3•THF 2. H2O2, NaOH A) + enantiomer OH B) C) OH D) + O H O H H E) OH Ans: E Topic: Hydroboration-Oxidation Section: 9.6

+ enantiomer OH OH OH + enantiomer enantiomer+ 1. BH3•THF 2. H2O2, NaOH II III I A) I B) II C) III D) I and II E) I and III Ans: E

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1. BH₃•THF 2. H2O2, NaOH A) + enantiomer OH OH B) H O O C) + enantiomer OH D) OH E) + enantiomer OH Ans: E

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1. BD3•THF 2. H2O2, NaOH OH D _HO D _D OH _D + enantiomer enantiomer+ + enantiomer enantiomer+ + enantiomer I II III IV V A) I B) II C) III D) IV E) V Ans: D Topic: Hydroboration-Oxidation Section: 9.6

1. BH3•THF 2. H2O2, NaOH A) HO B) + enantiomer HO C) + enantiomer HO D) + enantiomer OH E) HO HO

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Topic: Catalytic Hydrogenation Section: 9.7

52. What is the expected major product for the hydrogenation of an alkene? A) dihaloalkane B) alkane C) haloalkane D) alcohol E) ether Ans: B

53. Provide the major organic product(s) for the reaction shown below.

? H2, Pd/C ! A) Pd B) C) OH OH D) E) Ans: B

54. What product is formed when 5-chloro-1-methylcyclohexene is reduced with a Pt catalyst and H2?

A) 1-chloro-5-methylcyclohexane B) 1-chloro-3-methylcyclohexane C) 5-chloro-1-methylcyclohexane D) 3-chloro-1-methylcyclohexane E) None of the above

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Ans: B

55. What product is formed when trans-1,2-dimethylcyclohexane is reacted with Pd/C and H2?

A) No reaction

B) cis-1,2-dimethylcyclohexane

C) trans-3,4-dimethylhexane

D) trans-1,2-dimethylhexane

E) None of the above Ans: A

56. Which of the following reagents accomplishes the transformation shown below?

? A) H2/HCl B) H2/H2SO4 C) H2/Ni D) H2O/Ni E) H2O/H2SO4 Ans: C

57. Which of the reagents below are expected to convert cyclopentene into cyclopentane? A) H2 and Ni B) H2O C) Heat D) Zn, H3O+ E) Light Ans: A

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58. Which alkene would yield 3-methylpentane upon subjection to catalytic hydrogenation? I II III IV V A) I B) II C) III D) IV E) V Ans: B

59. How many moles of hydrogen (H2) are consumed in the catalytic reduction of 1

mole of 1,3-dibromocyclohexa-1,4-diene? A) 12

B) 2 C) 3 D) 4

E) None of the above Ans: B

60. How many moles of hydrogen (H2) are required to completely reduce 1 mole of cis-2,3,3-trimethylhepta-1,5-diene? A) 02 B) 1 C) 2 D) 3 E) 4 Ans: C

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61. Which of the catalysts listed are used in the homogenous catalytic hydrogenation of alkenes?

I) Ni II) Pt III) Wilkinson A) I B) II C) III D) I and II E) II and III Ans: C

62. In conducting a catalytic hydrogenation of an alkene, which catalyst listed is most likely soluble in the reaction medium?

A) Ni B) Pt C) Pd

D) Wilkinson

E) All of the above are soluble Ans: D

63. Wilkinson’s catalyst accomplishes which of the listed molecular transformations? A) syn addition of H2 to an alkene

B) anti addition of H2 to an alkene

C) syn dihydroxylation of an alkene

D) anti dihydroxylation of an alkene

E) oxidative cleavage of an alkene Ans: A

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64. For the catalytic hydrogenation of alkenes, select from below those most likely to function as a homogenous catalyst?

A) Wilkinson B) Ni C) Pd D) Pt E) Au Ans: A

65. Which of the following will yield 2-methylpentane upon catalytic hydrogenation? A) 2-methyl-1-pentene2

B) 2-methyl-2-pentene C) 4-methyl-2-pentene D) 4-methyl-1-pentene E) All of the above Ans: E

66. For the complete reduction of 1 mole of (3E,5E)-hepta-1,3,5-triene with H2 using a

Pd catalyst, how many moles of H2 are consumed?

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

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Topic: Catalytic Hydrogenation and Stereospecificity Section: 9.7

67. What products are produced from the reaction below?

II III IV I ? H2 Pt A) I, II, III B) II, III, IV C) I and IV D) II and III E) I, II, III, and IV Ans: A

Topic: Catalytic Hydrogenation and Stereospecificity Section: 9.7

68. Identify the major organic product generated from the reaction shown.!

I II III D D CH₃ D D CH3 D D CH3 IV CH3 D H V CH3 D + enantiomer + enantiomer +enantiomer + enantiomer + enantiomer ? D₂ Pd A) I B) II C) III D) IV E) V Ans: B

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Topic: Halogenation Section: 9.8

69. Which reaction intermediate is formed when 4-methylcyclohexene reacts with Br2

dissolved in CCl4? II III IV I V Br H3C H3C Br H3C Br Br Br Br A) I B) II C) III D) IV E) V Ans: B Topic: Halogenation Section: 9.8

70. What is the expected major product upon reaction of 1-pentene with Cl2?

A) 1-chloropentane B) 2-chloropentane C) 1,1-dichloropentane D) 2,2-dichloropentane E) 1,2-dichloropentane Ans: E

Topic: Halogenation and Stereospecificity Section: 9.8

71. Treating 2-methyl-2-pentene with Br2 is expected to produce which of the

following as the major product?

A) 2,3-dibromo-2-methylpentane B) 2,2-dibromo-2-methylpentane C) 3,3-dibromo-2-methylpentane D) 2-bromo-2-methylpentane E) 3-dibromo-2-methylpentane Ans: A

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Topic: Halohydrin Formation Section: 9.8

72. The expected intermediate formed during a halohydrin reaction is: A) a halonium ion.

B) the most stable carbocation with OH on the adjacent carbon. C) the most stable carbocation with X on the adjacent carbon. D) a cyclic oxonium ion.

E) the most stable carbanion. Ans: A

73. What major product is expected from the following reaction?

Br₂ ? H2O II III IV V I Br OH Br OH Br _OH _Br OH _Br _Br A) I B) II C) III D) IV E) V Ans: D

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Br₂, CH₃OH OH Br H₃CO Br Br OCH3 OCH3 Br I II III IV V +

enantiomer +enantiomer +enantiomer

+ enantiomer Br H3CO ? A) I B) II C) III D) IV E) V Ans: D

75. Which of the statements is most correct regarding the products expected from the halogenation reaction shown below?

Br2, CCl4 I CH3 Br Br C2H5 H H CH3 Br Br C2H5 H H II CH3 Br H C2H5 H Br III C2H5 Br H CH3 H Br IV ?

A) Equal amounts of I and II are produced. B) Equal amounts of III and IV are produced. C) Equal amounts of I and IV are produced. D) Equal amounts of II and III are produced. E) Equal amounts of I and III are produced. Ans: B

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76. For the halogenation reaction shown below, which of the following statements is correct regarding the expected products?

I2, CCl4 I II III C2H5 I I C2H5 H₃C H C2H5 I H C2H5 H3C I C2H5 I I C2H5 CH3 H IV C2H5 I CH₃ C2H5 H I ?

A) Equal amounts of I and II produced B) Equal amounts of III and IV produced C) Equal amounts of I and IV produced D) Equal amounts of II and III produced E) Equal amounts of I and III produced Ans: A

Topic: Halogenation, Regioselectivity, and Stereospecificity Section: 9.8

77. The reaction of Br2 with 1-methylcyclohexene, in the presence of ethylamine

(EtNH2), is expected to produce which of the following as the major product?

I II III IV V

+

+ enantiomer CH3 NHEt Br CH3 Br NHEt CH₃ NHEt Br CH₃ Br NHEt NHEt Br A) I B) II C) III D) IV E) V Ans: D

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Topic: anti dihydroxylation Section: 9.9

78. For the reaction sequence below, identify the expected major products.

1. MCPBA 2. H₃O+ ? A) + enantiomer O B) + enantiomer OH OH C) + enantiomer HO OH D) + enantiomer OH OH E) + enantiomer OH OH Ans: B

79. For the reaction sequence below, identify the expected major product(s).

1. MCPBA 2. H+_{, H} 2O ? HO OH H H H3CH2C CH2CH3 HO OH H H H3CH2C CH2CH3 HO OH H H H3CH2C CH₂CH₃ II III I A) I B) II C) III D) I and III E) II and III

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Ans: D

80. What are the major products for the following reaction sequence?

CH3 I II III IV 1. MCPBA 2. H3O+ ? OH CH3 OH CH3 OH OH CH3 OH OH OH CH3 OH A) I and II B) II and III C) III and IV D) I and III E) II and IV Ans: E

81. What is the major product for the following reaction sequence?

1. MCPBA OH OCH3 H3CO OH OH OCH3 OCH3 OH I II III IV V +

+ enantiomer +enantiomer OCH3 OCH3 2. [H₂SO₄], CH₃OH ? A) I B) II C) III D) IV E) V

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Ans: D

82. For the following dihydroxylation reaction which of the following statements is correct regarding the expected products?

I II III CH(CH3)2 OH OH CH2CH3 H₃CH₂C H CH(CH₃)₂ CH2CH3 H CH2CH3 HO HO CH(CH₃)₂ H3CH2C HO CH2CH3 OH H IV CH₂CH₃ OH CH₂CH₃ CH(CH₃)₂ H HO 1. MCPBA 2. H3O+ ?

A) Equal amounts of I and II produced B) Equal amounts of III and IV produced C) Equal amounts of I and IV produced D) Equal amounts of II and III produced E) Equal amounts of I and III produced Ans: E

83. An unknown alkene was reacted with MCPBA in dichloromethane, followed by work-up with H2O/H+. A racemic mixture of the compound shown below was

obtained. What is correct name of the starting alkene?

+ enantiomer OH OH A) (Z)-3-methylpent-2-ene B) (E)-3-methylpent-2-ene C) 2-methylpent-2-ene D) 2,3-dimethylbut-2-ene E) none of the above Ans: A

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Topic: syn Dihydroxylation Section: 9.10

84. Identify the expected major organic product resulting from the following reaction sequence. ? 1. KMnO4, NaOH Cold OH OH OH OH O O OH OH O O O H H I II III IV V A) I B) II C) III D) IV E) V Ans: A

85. Treatment of 1,2-dimethylcyclopentene with OsO4, followed by aqueous NaHSO3,

produces which of the following:

CH3 II III IV V I OH OH CH3 CH3 CH3 OH OH CH3 CH3 OH H H CH3 CH3 OH H CH3 CH₃ H A) I B) II C) III D) IV E) V Ans: A

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86. Identify the expected major organic product generated from the reaction sequence shown.! I II III OH OH CH3 OH OH CH3 OH OH CH₃ IV CH₃ OH H V CH₂OH OH +

+ enantiomer +enantiomer ? 1) OsO4 2) NaHSO3/H2O A) I B) II C) III D) IV E) V Ans: B

87. Which of the following alkene addition reactions occur(s) specifically in syn fashion?

A) dihydroxylation using OsO4, H2O2

B) addition of H2

C) hydroboration D) addition of HCl E) A, B, and C Ans: E

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1. OsO4, pyridine 2. H2O, NaHSO3 A) + enantiomer OH OH B) + enantiomer OH OH C) H O H O + D) OH O HO O +

E) None of the above Ans: A

Topic: Oxidative Cleavage Section: 9.11

89. Provide the expected major organic product of the reaction sequence shown.

1. O3 2. (CH3)2S, (DMS) ? I II III IV V O O O O O A) I and II B) IV and V C) I only D) II only E) III only

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Ans: E

90. Which of the following reagents effectively cleaves a carbon-carbon double bond? A) Cl2/hυ B) O O O H R C) H2SO4 D) cold KMnO4 E) O3/DMS Ans: E

91. How many carbonyls are generated upon treatment of the molecule below with ozone, followed by zinc metal and water?

A) 1 B) 2 C) 3 D) 4 E) 8 Ans: E

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92. Of the alkenes shown, which would produce the product shown below, upon treatment with ozone, followed by zinc metal and water?

C C C O C C C C O H H H H H H H H H H H H I II III IV V CH3 CH3 CH3 ? A) I B) II C) III D) IV E) V Ans: B

93. What is the expected major product of the reaction sequence shown below?

CH3 1. O3 2. Zn/H2O ? H3C O H3C O H O H O CH3 H O H O H O OH O CH3 O O I II III IV V A) I B) II C) III D) IV E) V Ans: A

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94. What are the expected major products from the reaction sequence shown below?

1. O3 2. Zn/H2O I II III IV V O O CO2H O O + + + + + O C H H C O O H O H H O OH HO O OH ? A) I B) II C) III D) IV E) V Ans: A

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Topic: Predicting Addition Products Section: 9.12

95. Which of the following alkene addition reactions occur(s) specifically in an anti fashion?

A) hydroboration-oxidation B) addition of Br2

C) addition of H2

D) addition of H2O in dilute acid

E) both A and B Ans: B

96. The Markovnikov product, resulting from an addition reaction to an unsymmetrical alkene, is formed because:

A) the product is statistically favored. B) steric hindrance favors its formation.

C) the reaction proceeds via the more/most stable carbocation. D) the reaction forms the more/most stable product.

E) All of the above are valid reasons Ans: C

1. BH3•THF 2. H2O2, NaOH A) OH B) + CO2 O OH C) D) OH + enantiomer E) + enantiomer OH OH

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Ans: A

98. What reagents are most likely to accomplish the transformation shown below?

? _OH A) 1. BH3 / 2. HO–, H2O2, H2O B) H+, H2O C) 1. Hg(OAc)2, H2O, THF / 2. NaBH4 D) 1. Hg(OAc)2, CH3OH / 2. NaBH4 E) NaOH, H2O Ans: A

99. Which reaction is not stereospecific?

I II III IV V Br₂/CCl₄ trans-2-Butene cis-2-Pentene trans-2-Hexene KMnO4, NaOH 2-Methyl-2-heptene 1-Methylcyclohexene D2/Pd Br2/H2O HBr Cold A) I B) II C) III D) IV E) V Ans: C

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100. The expected product(s) resulting from addition of Br2 to (E)-3-hexene would be:

A) a meso dibromide.

B) a mixture of optically active enantiomeric dibromides. C) a mixture of optically inactive enantiomeric dibromides. D) (Z)-3,4-dibromo-3-hexene.

E) (E)-3,4-dibromo-3-hexene. Ans: A

101. Which of the following alkenes will yield a meso dihalide when reacted with Br2/CCl4 at room temperature? A) B) C) D) E) Both B and D Ans: B

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102. What is the expected major product resulting from the acid-catalyzed hydration of 2,5-dimethyl-2-hexene? A) HO B) HO C) OH D) OH E) HO OH Ans: B

103. What is the expected major product resulting from treatment of (E)-3-methyl-3-hexene with Br2 in the presence of methanol, CH3OH?

A) Br OMe B) Br MeO C) OMe Br D) OMe Br

E) All of the above are produced in equal amounts Ans: A

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Topic: Synthetic Strategies Section: 9.13

104. To accomplish a Markovnikov addition of water to an unsymmetrical alkene, with minimal skeletal rearrangement, the best reagents would be:

A) water and dilute acid

B) water and concentrated acid

C) 1. Hg(OAc)2, H2O 2. NaBH4, NaOH

D) 1. BH3•THF 2. H2O2, NaOH

E) 1. OsO4, pyridine 2. NaHSO3, H2O

Ans: C

105. For the reaction sequence shown, what is the expected major elimination product?

1. HI 2. NaOMe, MeOH O I II III IV V I O A) I B) II C) III D) IV E) V Ans: B

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106. For the reaction sequence shown, what is the expected major elimination product?

1. HBr 2. NaOMe, MeOH I II III IV V A) I B) II C) III D) IV E) V Ans: D

107. What is the expected major product of the following reaction sequence?

1. HCl 2. t-BuOK, t-BuOH O I II III IV V A) I B) II C) III D) IV E) V Ans: C

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1. NaOEt, HOEt, heat 2a. Hg(OAc)₂, CH₃OH 2b. NaBH4, NaOH Br OCH3 OH OCH₃ OH O H3C I II III IV V A) I B) II C) III D) IV E) V Ans: A

Topic: Synthetic Strategies, anti Dihydroxylation Section: 9.13, 9.9

109. Which is the correct sequence of reaction steps necessary to complete the following transformation?

Br OH

OH

+ enantiomer ?

I. MCPBA II. NaOCH2CH3, CH3CH2OH III. H3O+ or -OH IV. 1) OsO4 then 2) NaHSO3/H2O

A) I then II then III B) II then I then III C) II then IV D) III then I

E) I then IV then II then III Ans: B

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1. NaOEt, EtOH, heat 2a. BH₃•THF 2b. H2O2, NaOH Cl HO OH OH +

enantiomer enantiomer+ enantiomer+ OH HO HO OH + enantiomer I II III IV V A) I B) II C) III D) IV E) V Ans: C

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1. NaOEt, EtOH, 70 °C 2a. O3, CH2Cl2, -78 °C 2b. DMS Br H A) O O B) OH OH C) O O D) CH HC O O E) O O H Ans: A

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1. OsO4, pyridine 2. H2O, NaHSO3 A) + enantiomer OH OH B) + enantiomer OH OH C) + enantiomer OH OH D) H O H O + E) + enantiomer OH OH OH Ans: A

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1. t-BuOK

2. KMnO₄, NaOH, cold Cl A) O OH O + B) + CO2 OH O C) + enantiomer OH OH D) + enantiomer OH OH E) + enantiomer OH Ans: C

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1. t-BuOK, t-BuOH 2a. O3, CH2Cl2 2b. Me₂S Cl A) + O H H O B) H O O C) OH OH D) + enantiomer OH OH E) O H O H + O H Ans: A

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1. t-BuOK, t-BuOH 2. HBr Cl Br Br Br Br Br Cl I II III IV V A) I B) II C) III D) IV E) V Ans: C

116. For the following reaction sequence, which molecule is an expected major product?

1. t-BuOK

2a. OsO4, pyridine

2b. H₂O, NaHSO₃ Br A) OH HO B) OH OH C) OH OH D) E) Br OH

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Ans: A

1. NaOEt, EtOH, 70 °C 2a. O3, CH2Cl2, -78 °C 2b. DMS Br H A) O O B) OH OH C) O O D) CH HC O O E) O O H Ans: E

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118. For the following reaction sequence identify the expected major organic products and provide their stereochemical relationship.

1. t-BuOK, t-BuOH 2a. BH3•THF 2b. H₂O₂, NaOH I II III IV OH HO Br OH HO OH HO OH HO

A) I and II; enantiomers B) III and IV; enantiomers C) I and II; diastereomers D) II and III; diastereomers E) III and IV; diastereomers Ans: D

119. For the following reaction sequence identify the total number, frequency and types of stereoisomeric compounds expected as products.

Br

1. NaOEt, HOEt, heat 2a. Hg(OAc)2, CH3OH

2b. NaBH₄, NaOH

A) 2 total stereoisomers; 1 set of enantiomers B) 4 total stereoisomers; 2 sets of enantiomers C) 4 total stereoisomers; 4 diastereoisomers D) 8 total stereoisomers; 4 sets of enantiomers E) 8 total stereoisomers; 8 diastereomers Ans: E

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Short Answer Questions:

Topic: Introduction to Addition Reactions Section: 9.1

120. π bonds are quite susceptible to reaction with electron-seeking reagents, also referred to as ____________________.

Ans: electrophiles

Topic: Regioselectivity Section: 9.3

121. The rule that correctly predicts the regiochemistry of most ionic additions to alkenes is called ____________________.

Ans: Markovnikov's Rule

122. For the following reaction sequence provide the expected major organic product(s). Include all stereoisomers showing relevant stereochemistry.

HI

Ans:

I I

123. Provide the structure(s) of the expected major organic product(s) generated upon completion of the following reaction scheme:

HBr ROOR (CH3)2CHCH2CH CH2 ?

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124. The reaction of HCl with 2-ethyl-1-pentene or HCl with 3-methyl-2-hexene results in the identical major product of 3-chloro-3-methylhexane. Provide a mechanistic scheme showing the reaction of each alkene with HCl, including the intermediate and product. Provide a brief explanation how the different alkene reactants were transformed into the same product.

Ans: Cl most stable carbocation H Cl H Cl Cl–

Electrophilic addition of a proton in the reaction between HCl and both alkenes will result in formation of the most stable intermediate carbocation. Addition of Cl– to the tertiary carbocation formed in both cases results in the observed product. The reason for the identical major product is a consequence of regioselective addition to the double bond forming the same tertiary carbocation intermediate.

125. When the two constitutional isomers, 3,3-dimethyl-1-butene and 2,3-dimethyl-2-butene, are reacted with HCl the same major product is formed. Provide a mechanistic explanation for the observation.

Ans: HCl Cl HCl most stable carbocation 3,3-dimethyl-1-butene 2,3-dimethyl-2-butene Cl– 2-chloro-2,3-dimethylbutane

For the unsymmetrical 3,3-dimethyl-1-butene, the carbocation formed is 2°, but can readily undergo a methyl shift to form the more stable 3° carbocation, which is the same as that formed from 2,3-dimethyl-2-butene. The addition of the chloride ion to the carbocation forms the identical product, 2-chloro-2,3-dimethylbutane.

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126. Addition of HI to the alkene of the cyclobutane in the scheme below, results in a significant yield of the product shown. What other product(s) might also be obtained? Explain with a mechanism and brief discussion the observation of the given product as well as others that may arise.

HI I Ans: H+ _fast I– I I I– ring expansion methyl shift I– alternative 2 alternative 3 I 1,2 addition alternative 1

Regioselective addition of the proton of HI generates a secondary carbocation. Rearrangement to a more stable 3o carbocation can occur by two alternative pathways (1 and 2). Pathway 1 results in relief of ring strain by expansion to a more stable 5-membered ring. The second pathway involving a methyl shift is less likely; ring strain is not relieved and becomes worse with incorporation of an sp2 carbon (bond angle 120°)

into the cyclobutane (bond angle 90°). The third pathway occurs if addition of iodide to occurs before carbocation rearrangement. The first pathway is most likely, resulting in the observed product.

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Topic: Acid-Catalyzed Hydration Section: 9.4

127. For the following reaction sequence provide the expected major organic product(s). Include all stereoisomers showing relevant stereochemistry.

H3O+

?

Ans:

OH

128. For the following reaction sequence provide the expected major organic product(s). Include all stereoisomers and clearly show relevant stereochemistry.

H3O+

?

Ans:

HO

OH

H₃O+

?

Ans:

OH OH

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130. The transformation shown below generates an achiral product from a chiral starting material. Provide the structure of the expected product and a mechanism explaining the transformation. Briefly explain why the product formed is achiral.

H3O+ ? H Ans: OH H H+ H H O H O H H :B O H Hydride shift

Upon addition of the proton to the alkene a 2° carbocation is formed that undergoes a hydride shift to form a more stable 3° carbocation. The 3° carbocation is located in the center of the chain, and being sp2 hybridized is planar. Addition of water to the central carbon produces a product with no stereocenter and is thus achiral.

131. A reaction that could potentially yield two or more constitutional isomers, but as in hydroboration-oxidation produces only one isomer, is said to be _____________________.

Ans: regioselective

132. Any proper mechanism of hydroboration-oxidation must explain the observed _________ addition of the H and OH to the alkene as well as the _____________ regiochemistry.

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1. BH3•THF

2. H2O2, NaOH

CH3CH2C(CH3)2CH CH2 ?

Ans: OH

134. Provide the expected major organic product from the reaction shown below. Provide a brief explanation of any regioselectivity the reaction is expected to produce.

Br2 / H2O

Ans:

Br OH

The alcohol will be found at the tertiary carbon, being the more substituted carbon. Initial formation of the bromonium ion will favor attack of the water at the more substituted carbon which is more capable of stabilizing the partial positive charge that develops in the transition state.

135. For the following transformation below, provide a detailed step-wise mechanism showing the electron flow using the curved arrow formalism.

HO Br2 + HBr O Br Ans: HO Br Br HO Br O Br H Br– + HBr O Br !

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136. For the following reaction draw out the expected major organic product(s). Include regiochemical and/or stereochemical details as relevant, and provide a short justification for the product(s) drawn.

Br₂, H₂O ? Ans: H Br OH H Br OH +

The reaction takes place with Markovnikov regioselectivity and anti stereospecificity, giving a racemic mixture of the halohydrin as the major product.

137. Draw Fischer projection formulas of the major product of the reaction between (E)-2-methyl-3-hexene and aqueous Br2.

Ans: CH(CH3)2 H Br C2H5 HO H CH(CH3)2 H Br C2H5 OH H CH(CH3)2 Br H C2H5 H HO CH(CH3)2 Br H C2H5 H OH Br2 H₂O

The reaction takes place with anti stereospecificity. Since the alkene is symmetrically substituted, Markovnikov rule is not applicable, and the reaction is not regioselective. The product mixture would therefore consist of 2 pairs of enantiomers, which are constitutional isomers of each other.

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1. O3 2. (CH3)2S, (DMS) ? Ans: O H and O H

Topic: Predicting Reaction Products: Halohydrin Formation and Stereospecificity Section: 9.12

139. Predict the structure(s) of the expected major organic product(s) of the following reaction. Include regiochemical and/or stereochemical details as needed.

? Br2

CH₃OH H

Ans: Br OCH3 _Br OCH3

H H

+

The reaction takes place with Markovnikov regioselectivity and anti stereospecificity. As the product is chiral, the products are diastereomers.

Topic: Predicting Reaction Products: syn Dihydroxylation Section: 9.12

140. Draw Fischer projection formula(s) of the major product(s) of the reaction between (Z)-2-methyl-3-hexene and cold, alkaline KMnO4.

Ans: CH(CH3)2 OH OH C₂H₅ H H CH(CH3)2 HO HO C2H5 H H KMnO₄ cold, dil

The reaction takes place with syn stereospecificity, giving a racemic mixture of the diol product.

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Topic: Predicting Reaction Products: syn Dihydroxylation Section: 9.12

141. Draw Fischer projection formula(s) of the major product(s) of the reaction between (Z)-3-methyl-3-hexene and catalytic OsO4 NMO.

Ans: CH2CH3 OH OH C₂H₅ H₃C H CH2CH3 HO HO C2H5 CH3 H OsO4 NMO

The reaction takes place with syn stereospecificity, giving a racemic mixture of the diol product.

Topic: Predicting Reaction Products: anti Dihydroxylation Section: 9.12

142. Draw Fischer projection formula(s) of the major product(s) of the reaction between (Z)-3-methyl-3-hexene and MCPBA, followed by acidic water.

Ans: CH₂CH₃ CH3 OH C2H5 HO H CH2CH3 H₃C HO C₂H₅ OH H 1) MCPBA 2) H3O+

The reaction takes place with anti stereospecificity, giving a racemic mixture of the diol product.

Topic: Predicting Reaction Products: Oxidative Cleavage Section: 9.12

143. Predict the product(s) of the oxidation of 2,3,4-trimethyl-1,5-heptadiene upon treatment with O3 followed by dimethylsulfide (DMS).

Ans: O O OH O OH 1) O3 2) DMS CO2 H2O

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144. A common problem in the acid catalyzed hydration of alkenes is the formation of an ether byproduct. Explain the formation of the ether byproduct in relation to the reaction below: H3O+ H2O _OH O Ans: OH –H+ O

Topic: Predicting Reaction Products: Halohydrin Formation and Stereospecificity Section: 9.12

145. Identify the structure(s) of the expected major organic product(s) of the following reaction. Draw the products in the expected chair conformations and include regiochemical and/or stereochemical details as needed.

H ? Br₂ CH3OH Ans: H OCH3 Br H OCH3 Br H OCH3 Br H CH₃O Br H H₃CO Br

The reaction takes place with Markovnikov regioselectivity and anti stereospecificity. The starting material is shown as a single enatiomers, and thus produces two diastereomers. The product containing the cis fused rings is capable of a ring flip.

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146. Starting with (2R,3R)-2-chloro-3,4-dimethylpentane, a) draw the expected major product for each step, including regiochemical and stereochemical details when needed. In addition, b) briefly explain the mechanistic rational for each transformation. i. t-BuOK/t-BuOH, heat ii. MCPBA/CH2Cl2 iii. H3O+ Ans: Cl H3C H H MCPBA t-BuOK/t-BuOH (E2: Hofmann elimination) _H 3C H H3C H O H O H (S)-2-((R)-1,2-dimethylmethylpropyl) oxirane H3C H H (R)-3,4-dimethylpent-1-ene + CH2Cl2 syn addition (2R,3R)-2-chloro-3,4-dimethylpentane (R)-2-((R)-1,2-dimethylmethylpropyl) oxirane H3O+ H3C H H3C H HO HO H HO _H OH (2R,3R)-3,4-dimethylpentane-1,2-diol (2S,3R)-3,4-dimethylpentane-1,2-diol

Hofmann elimination occurs upon heating with the bulky potassium tert-butoxide base, through an E2 elimination. Epoxidation with MCPBA is stereospecific (syn), giving a racemic (R,R & S,R) epoxide. Ring opening of the epoxide under acidic conditions is regio- and stereospecific.

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147. For the following transformation a) identify the starting material with correct stereochemistry and b) provide a complete reaction mechanism, including stereochemistry, to account for the product shown.

1) MCPBA 2) MeOH, [H2SO4] MeO OH ? Ans: O O Cl O H O S O O OH O H O H OH H3C O H O H3C H B: O H O H3C MeO _OH Step 1

Step 1 involves the epoxidation of the (E) alkene by MCPBA, showing only the enantiomer leading given product. Acid catalyzed ring opening of the epoxide would occur with regiospecific addition of MeOH to the 3° carbon. Deprotonation by a general base (likely MeOH in this example) provides the product, which upon σ bond rotation has the same conformation as the product given in the question.

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148. Consider the information given below and identify the structure of the unknown compound A, with a molecular formula of C8H14. Compound A reacts with

Br2/CCl4. Upon reaction with excess H2/Ni 1-ethyl-2-methylcyclopentane is

produced. Subjecting A to ozonolysis, the product shown below is produced as the

major organic product. Draw the correct structure of compound A, and provide a

brief and clear explanation relating the data provide with the structure selected.

O O

Ans: A must be 3-ethyl-4-methylcyclopentene. This given data can be explained as shown below:

O O

Reacts with Br2,CCl4: A must contain a π bond

H2, Ni

ozonolysis

C8H14

A must contain the

same carbon skeleton as the product after hydrogenation, and a π bond

The location of the π bond position in A is identified from the structure of the ozonolysis product

A