Chapter 7

Chapter Seven

MULTIPLE CHOICE QUESTIONS

Topic: NomenclatureSection: 4.3, 4.5, 7.2Difficulty Level: Easy

1. The correct IUPAC name for the following compound is:

A) 2-Bromo-4-methylenehexaneB) 2-(2-Bromopropyl)-1-buteneC) 4-Bromo-2-ethyl-1-penteneD) 2-Bromo-4-ethyl-1-penteneE) 2-Bromo-4-ethyl-4-pentene

Ans: C

Topic: Nomenclature; StereochemistrySection: 4.3, 4.5, 7.2Difficulty Level: Medium

2. Name the following compound:OCH3

A) (cis)-3-methoxyhex-3-eneB) (Z)-4-methoxyhex-4-eneC) (Z)-3-methoxyhex-3-eneD) (E)-3-methoxyhex-3-eneE) 3-methoxyhex-3-ene

Ans: C

386


3. Name the following compound:

HO

A) (E)-4-phenyl-4-methylbut-3-en-1-olB) (E)-4-phenylpent-3-en-1-olC) (Z)-4-phenylpent-3-en-1-olD) (Z)-4-phenyl-4-methylbut-3-en-1-olE) (E)-4-benzylpent-3-en-1-ol

Ans: B


4. Which structure represents (Z)-4-bromohexa-1,3-diene? A) Br

B)

BrC)

BrD) Br

E) None of the aboveAns: C

387


5. Which structure represents (E)-1-bromo-2-methylhex-2-ene? A) Br

B) Br

C)

BrD) Br

E) None of the aboveAns: A


6. Which structure represents (Z)-1,4-dichlorohex-3-en-1-yne? A)

Cl

Cl

B) ClCl

C)

Cl

Cl

D)

Cl

Cl

E) None of the aboveAns: B

388

Topic: NomenclatureSection: 4.5, 7.2Difficulty Level: Easy

7. A correct IUPAC name for the following compound is:

A) 3,3,5-trimethyl-2-hexeneB) 3-isobutyl-3-isopropyl-2-propeneC) 3-isobutyl-4-methyl-2-penteneD) 3-(1-methylethyl)-5-methyl-2-hexeneE) None of the above

Ans: E



A) 4,5-Dimethyl-3-propyl-2-hexeneB) 4,5-Dimethyl-3-propyl-1-hexeneC) 3-(2,3-Dimethylpropyl)-1-hexeneD) 2,3-Dimethyl-4-isopropyl-5-hexeneE) 2,3-Dimethyl-4-propyl-5-hexene

Ans: B

389


9. Select the structure of 4–ethyl-2,3-dimethyl-2-heptene.A)

B)

C)

D)

E)

Ans: B

Topic: NomenclatureSection: 4.5, 7.2Difficulty Level: Medium


A) (E)-2-Bromo-3-chloro-5-methyl-2-hexeneB) (E)-2-Bromo-3-chloro-5-methyl-3-hexeneC) (Z)-2-Bromo-3-chloro-5-methyl-3-hexeneD) (Z)-2-Bromo-3-chloro-5-methyl-2-hexeneE) (E)-2-Methyl-5-bromo-4-chloro-4-hexene

Ans: A

390

Topic: Nomenclature; StereochemistrySection: 4.3, 4.5, 5.7, 7.2Difficulty Level: Medium

11. Name the following compound:Br

A) (S,Z)-3-bromo-4-methylhex-2-eneB) (S)-3-bromo-4-methylhex-2-eneC) (S,Z)-4-bromo-3-methylhex-4-eneD) (S,E)-3-bromo-4-methylhex-2-eneE) (R,E)-3-bromo-4-methylhex-2-ene

Ans: A

Topic: Nomenclature; StereochemistrySection: 4.3, 4.5, 5.7, 7.2Difficulty Level: Medium


Br

Br

A) (S,E)-2,4-dibromo-3-methylpent-2-eneB) (R,Z)-2,4-dibromo-3-methylpent-2-eneC) (R,E)-2,4-dibromo-3-methylpent-3-eneD) (S,E)-2,4-dibromo-3-methylpent-3-eneE) (R,E)-2,4-dibromo-3-methylpent-2-ene

Ans: E

391

Topic: Nomenclature; StereochemistrySection: 4.3, 4.5, 5.7, 7.2Difficulty Level: Hard


OH

A) (R,Z)-5-phenyloct-5-en-3-olB) (R,Z)-5-benzyloct-5-en-3-olC) (R,E)-5-phenyloct-5-en-3-olD) (R,E)-5-benzyloct-5-en-3-olE) (R,E)-5-benzyloct-3-en-6-ol

Ans: B

Topic: Nomenclature; StereochemistrySection: 4.3, 4.5, 5.7, 7.2Difficulty Level: Hard

14. Which structure represents (R,Z)-5-methylhept-2-ene? A)

B)

C)

D)

E) None of the aboveAns: D

392

Topic: Nomenclature; StereochemistrySection: 4.3, 4.5, 4.6, 5.7, 7.2Difficulty Level: Medium

15. Name the following compound:Cl

A) (S,E)-3-chlorohex-4-en-1-yneB) (R,E)-3-chlorohex-2-en-5-yneC) (S,E)-3-chlorohex-2-en-5-yneD) (R,E)-3-chlorohex-4-en-1-yneE) (R,E)-3-chloropent-4-en-1-yne

Ans: D

Topic: Alkene Stability, Heats of Hydrogenation and CombustionSection: 7.3Difficulty Level: Easy

16. Which molecule would have the lowest heat of hydrogenation?

A) IB) IIC) IIID) IVE) V

Ans: A

393


17. Heats of hydrogenation data would be useful in comparing the relative stabilities of which of the following substances?

A) I, II, IIIB) III, IVC) I, II, VD) Heats of hydrogenation data would not be a useful way to compare relative stabilities of

any of the substances.E) All of the above substances could effectively be compared using heats of hydrogenation

data.Ans: C


18. Which alkene would liberate the most heat per mole when subjected to catalytic hydrogenation?

A)B)C)

D)

E)Ans: A

394


19. Which alkene is most stable?


Ans: A

Topic: Alkene Stability, Heats of Hydrogenation and CombustionSection: 7.3Difficulty Level: Medium

20. Concerning the relative stabilities of alkenes, which is a false statement?A) Unless hydrogenation of the alkenes gives the same alkane, heats of hydrogenation

cannot be used to measure their relative stabilities.B) In general, the greater the number of alkyl groups attached to the carbon atoms of the

double bond, the greater the stability of the alkene.C) The greater the quantity of heat liberated on combustion or hydrogenation of an alkene,

the greater its energy content.D) trans-Cycloalkenes are always more stable than the cis-isomers.E) Heats of combustion can be used to measure the relative stabilities of isomeric alkenes,

even though their hydrogenation products are not identical.Ans: D

395

Topic: Alkene Synthesis, Reaction MechanismsSection: 7.6Difficulty Level: Easy

21. Which product (or products) would be formed in appreciable amount(s) when trans-1-bromo-2-methylcyclohexane undergoes dehydrohalogenation upon treatment with sodium ethoxide in ethanol?

A) IB) IIC) IIID) IVE) More than one of these

Ans: B

Topic: Alkene SynthesisSection: 7.6Difficulty Level: Easy

22. Your task is to convert 2-bromobutane to 1-butene in highest yield. Which reagents would you use?

A) KOH/H2OB) KOH/CH3OHC) CH3ONa/CH3OHD) CH3CH2ONa/CH3CH2OHE) (CH3)3COK/(CH3)3COH

Ans: E

396


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

OTs

EtOH, EtONa

heat

A) CH3CH2(CH3)C=CHCH3

B) CH3CH2(CH3)CHCH=CH2

C) CH3CH2(CH3)CHCH(OCH2CH3)CH3

D) None of the aboveE) No reaction

Ans: A



Cl

t-BuOH, t-BuOK

A)

Ot-BuB)

C)

D)

E)

Ans: E

397



t-BuOH, t-BuOKI

A)

B)

C)

D)


398



EtONa, EtOH

heatI

A)

B)

C)

D)


399


27. What is the major product for the following reaction?Cl EtOH, EtONa

heat

A)

B)

C)

D)

E)

Ans: A

400



t-BuOK, t-BuOHBr

A)

B)

C)

D)

E)

Ans: E

401

Topic: Alkene SynthesisSection: 7.6Difficulty Level: Medium


EtONa, EtOH

heatBr

A)

B)

C)

D)

E) More than one of the aboveAns: C

402

Topic: Alkene Synthesis, Nomenclature, Reaction MechanismsSection: 7.6Difficulty Level: Medium

30. Dehydrohalogenation of tert-pentyl bromide will produce 2-methyl-1-butene as the chief product when:

A) CH3COONa is employed as the base.B) KOH/C2H5OH is employed as the base.C) CH3CH2ONa/CH3CH2OH is employed as the base.D) (CH3)3COK/(CH3)3COH is employed as the base.E) any base is used, as long as the temperature is sufficiently high.

Ans: D

Topic: Alkene SynthesisSection: 7.6Difficulty Level: Hard


Br

EtOH, EtONa

heat

A)

OEtB)

C)

D)

E)

Ans: C

403

Topic: Alkene SynthesisSection: 7.6Difficulty Level: Hard


Cl

EtOH, EtONa

heat

A)

OEtB)

C)

D)

E)

Ans: B

404

Topic: Alkene SynthesisSection: 6.5, 7.6Difficulty Level: Medium


OTs

1. NaI, acetone

2. t-BuOH, t-BuOK

A)

B)

C)

D)

E)

Ans: C

405

Topic: Alkene SynthesisSection: 6.5, 7.6Difficulty Level: Hard


Cl

1. NaI, acetone

2. t-BuOH, t-BuOK

A)

B)

C)

D)

E)

Ans: D

406



Cl

1. NaI, acetone

2. NaOH, EtOH, heat

A)

B)

C)

D)

E)

Ans: C

407



Br

1. NaI, acetone

2. EtONa, EtOH, heat

A)

B)

C)

D)

E)

Ans: B

408

Topic: Alkene Synthesis, Reaction MechanismsSection: 6.5, 6.16, 7.6Difficulty Level: Medium

37. Which compound listed below would you expect to be the major product when 2-bromo-2-methylbutane is refluxed with KOH/ethanol?

A)

B)

C)

D)

E)

Ans: D

Topic: Alkene SynthesisSection: 7.6BDifficulty Level: Easy

38. Zaitsev's rule states that:A) In electrophilic addition of an unsymmetrical reagent to an unsymmetrical alkene, the

more positive portion of the reagent will become attached to the carbon of the double bond bearing the greater number of hydrogen atoms.

B) An equatorial substituent in cyclohexane results in a more stable conformation than if that substituent were axial.

C) E2 reactions occur only if the -hydrogen and leaving group can assume an anti-periplanar arrangement.

D) When a reaction forms an alkene, and several possibilities exist, the more (or most) stable isomer is the one which predominates.

E) The order of reactivity of alcohols in dehydration reactions is 3º > 2º > 1º.Ans: D

409

Topic: Alkene SynthesisSection: 7.6CDifficulty Level: Easy

39. Regarding the use of potassium tert-butoxide as a base in E2 reactions, it is incorrect to state that:

A) this base is more effective than ethoxide ion, because it (KO-t-Bu) is the more basic of the two.

B) it tends to give the anti-Zaitsev, i.e., Hofmann, product.C) it is more reactive in dimethyl sulfoxide than it is in tert-butyl alcohol.D) it favors E2 reactions over competing SN2 reactions.E) it will form, predominantly, the more stable alkene.

Ans: E

Topic: Alkene Synthesis, Reaction MechanismsSection: 7.6CDifficulty Level: Easy

40. What is the major product of the reaction,

A) (CH3)2C=C(CH3)2

B) (CH3)3C–CH=CH2

C) (CH3)2C=CHCH3

D) (CH3)2C=CHCH2CH3

E) None of theseAns: B

410

Topic: Alkene Synthesis, Reaction MechanismsSection: 7.6CDifficulty Level: Easy

41. Which compound would be the major product?

A)

B)

C)

D)

E)

Ans: E

411

Topic: Carbocation Stability, RearrangementSection: 7.7Difficulty Level: Easy

42. Which statement(s) is/are true of acid-catalyzed alcohol dehydrations?A) Protonation of the alcohol is a fast step.B) Formation of a carbocation from the protonated alcohol is a slow step.C) Rearrangements of less stable carbocations to more stable carbocations are common.D) Loss of a proton by the carbocation is a fast step.E) All of the above

Ans: E

Topic: Alkene Synthesis, Reaction MechanismsSection: 7.7Difficulty Level: Easy

43. Which product(s) would be produced by acid-catalyzed dehydration of 2-methyl-2-pentanol?

A)

B)

C)

D)

E)

Ans: B

412

Topic: Alkene Synthesis; Alcohol DehydrationSection: 7.7Difficulty Level: Easy

44. Which one of the following alcohols would dehydrate most rapidly when treated with sulfuric acid?


Ans: B

413


45. Which mechanistic step in the acid-catalyzed dehydration of 3,3-dimethyl-2-butanol is the rate determining step?

A)

OH

+ H3O+

OH2

+ H2O

Step 1:

B)

OH2

+ H2O

Step 2:

C)

D)

E)

Ans: B

414


46. Which alcohol would be most easily dehydrated?A)

B)

C)

D)

E)

Ans: A


47. Which alcohol would be most easily dehydrated?


Ans: B

415

Topic: Carbocation StabilitySection: 7.7Difficulty Level: Medium

48. Which alcohol would initially produce the most stable carbocation when treated with concentrated H2SO4?

A)

B)

C)

D)

E)

Ans: A

Topic: Carbocation Stability, RearrangementSection: 6.10, 6.17, 7.7Difficulty Level: Hard

49. Carbocations are frequent intermediates in acidic reactions of alkenes, alcohols, etc. What do carbocations usually do? They may:

A) rearrange to a more stable carbocation.B) lose a proton to form an alkene.C) combine with a nucleophile.D) react with an alkene to form a larger carbocation.E) do all of the above.

Ans: E

416

Topic: Carbocation Stability, RearrangementSection: 6.11B, 7.7BDifficulty Level: Easy

50. Which of the following carbocations would NOT be likely to undergo rearrangement?A)

B)

C)

D)

E)

Ans: C

Topic: Carbocation Stability, RearrangementSection: 7.8Difficulty Level: Hard

51. Neopentyl alcohol, (CH3)3CCH2OH, cannot be dehydrated to an alkene without rearrangement. What is the chief product of dehydration?


Ans: B

417

Topic: Carbocation Stability, RearrangementSection: 5.12, 6.10, 6.17, 7.8Difficulty Level: Medium

52. What is the major product of the reaction between methanol and (2R,3S)-2-bromo-3-methylpentane at room temperature?

A)

B) OCH3

C)

D)

H3CO

E) Both A) and C) Ans: D

Topic: Carbocation Stability, RearrangementSection: 6.10, 6.17, 7.8Difficulty Level: Easy

53. Rearrangements are likely to occur in which of the following reaction types?A) SN1 reactionsB) SN2 reactionsC) E1 reactionsD) E2 reactionsE) Both SN1 and E1 reactions

Ans: E

418

Topic: Carbocation Stability, RearrangementSection: 6.10, 6.17, 7.8Difficulty Level: Easy

54. What is the major product of the reaction of the following reaction?I

ethanol, 20 oC

A)CH3CH2O

B) OCH2CH3

C)

D)

E) More than one of the aboveAns: A

419

Topic: Alkene SynthesisSection: 6.10, 6.17, 7.8Difficulty Level: Easy


EtOH, heatBr

A)

B)

C)

D)

E) More than one of the aboveAns: E

420

Topic: Alkene SynthesisSection: 6.10, 6.17, 7.8Difficulty Level: Medium


EtOH, heatI

A)

B)

C)

D)


421



EtOH, heatCl

A)

B)

C)

D)

E)

Ans: D

422


58. What is the major product of the reaction of the following reaction?Cl

EtOH, heat

A)

B)

C) OEt

D)

E)

Ans: D

423


59. What is the major product of the reaction of the following reaction?

OTs

EtOH, heat

A)

B)

C)

OEtD)


424


60. What is the major product of the reaction of the following reaction?

CH3OH, heat

Cl

A)

H3CO

B)

C)

D)

E)

Ans: E

425

Topic: Carbocation Stability, RearrangementSection: 4.16, 6.10, 6.17, 7.3, 7.8Difficulty Level: Medium

61. What is the major product of the reaction of the following reaction sequence?Br

1. H2, Ni

2. EtOH, heat

A)

B)

C)

D) OEt

E) A mixture of A) and B)Ans: C

426

Topic: Alkene Synthesis, Reaction Mechanisms, Carbocation RearrangementsSection: 7.7, 7.8Difficulty Level: Medium

62. Which alkene would you expect to be the major product of the following dehydration?


Ans: C

427

Topic: Alkene Synthesis, Reaction Mechanisms, Carbocation RearrangementsSection: 7.7, 7.8Difficulty Level: Hard

63. What will be the major product of the following reaction?

A)

B)

C)

D)

E)

Ans: A

428

Topic: Alkene Synthesis, NomenclatureSection: 7.6C, 7.7, 7.10Difficulty Level: Medium

64. Which of the following reactions would yield 3,3-dimethyl-1-butene in a reasonable percentage yield (i.e., greater than 50%)?

A)

B)

C)

D) All of theseE) Answers B) and C) only

Ans: B

Topic: Alkyne SynthesisSection: 7.11Difficulty Level: Easy

65. Which reaction would yield 2-butyne?A) CH3CC:Na + CH3Br B) CH3CH2Br + HCC:Na C) CH3:Na + HCCCH3 D) More than one of theseE) None of these

Ans: A

429

Topic: Alkyne SynthesisSection: 3.6, 7.11, 7.12Difficulty Level: Hard

66. Which reaction conditions would not yield 2-butyne from 1-propyne?A) a. EtONa, EtOH

b. CH3IB) a. CH3Li, THF

b. CH3IC) a. NaNH2, NH3 (liq)

b. CH3ID) a. NaCH2CH3, THF

b. CH3IE) More than one of these

Ans: A

Topic: Alkene Synthesis, Nomenclature, Reaction MechanismsSection: 7.6, 7.7, 7.11, 7.12Difficulty Level: Easy

67. Which of the following reactions would yield 2-pentyne?A)

B)

C) Br

Br

CH3OH

D)

E)

Ans: B

430

Topic: Alkyne SynthesisSection: 7.10, 7.11, 7.12 Difficulty Level: Medium

68. Which of the following methods could be used to synthesize 4,4-dimethyl-2-hexyne?A)

B)

C)

D) More than one of theseE) None of these

Ans: D

Topic: Alkyne SynthesisSection: 7.11, 7.12Difficulty Level: Easy

69. Which statement is/are true about acetylide anions?A) They do not alkylate with secondary alkyl halides.B) Primary alkyl halides are best suited for alkylation.C) In the presence of tertiary alkyl halides, the acetylide anion acts as base to give an

elimination product.D) Only two of the above are true.E) All of the statements are true.

Ans: E

431

Topic: Alkyne SynthesisSection: 7.11, 7.12Difficulty Level: Medium

70. Which reaction would not result in alkylation of the acetylide anion?A)

LiBr

B) Cl

LiC)

BrLiD)

OTs

LiE) None of the above

Ans: C

Topic: Alkyne SynthesisSection: 7.11, 7.12Difficulty Level: Medium

71. Which reaction would not primarily proceed via an SN2 mechanism?A)

LiBr

B) Cl

LiC)

BrLiD)

OTs

LiE) All of them proceed via SN2

Ans: C

432

Topic: Alkene/Alkyne Reactions, Reaction MechanismsSection: 3.16, 7.13Difficulty Level: Easy

72. Which would be the major product of the following reaction sequence?1a. NaNH2, NH3 (liq.)1b. T3O+

2. H2, Pd/C

A)

CH2CH3B)

CH=CHTC)

CH=CH2D)

CH2CH2T


Topic: Structure ElucidationSection: 2.16, 4.16, 7.13Difficulty Level: Medium

73. An unknown compound, B, has the molecular formula C7H12. On catalytic hydrogenation 1 mol of B absorbs 2 mol of hydrogen and yields 2-methylhexane. B has significant IR absorption band at about 3300 and 2200 cm-1. Which compound best represents B?

A) 3-methyl-1-hexyneB) 5-methyl-2-hexyneC) 5-methyl-1,3-hexadieneD) 5-methyl-1-hexyneE) 2-methyl-1,5-hexadiene

Ans: D

Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation

433

Section: 2.16, 4.16, 4.17, 7.13Difficulty Level: Easy

74. A compound X with the formula C7H10 undergoes catalytic hydrogenation to produce a compound Y with the formula C7H14. What could be true of X?

A) X might have one triple bond and one ring.B) X might have two double bonds and one ring.C) X might have one double bond and two rings.D) X might have one double bond and one triple bond.E) More than one of the above

Ans: E

Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation Section: 2.16, 4.16, 4.17, 7.13Difficulty Level: Medium

75. A compound, C6H10, which reacts with 2 mol of hydrogen over a platinum catalyst and which shows an IR absorption band at approximately 3300 cm-1 could be:


Ans: C

Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation

434

Section: 2.16, 4.16, 4.17, 7.13Difficulty Level: Medium

76. What is the structure of a compound with formula C6H10 which has IR absorption at approximately 3300 cm-1 and which can be catalytically reduced with hydrogen to 2-methylpentane?

A)

B)

C)

D)

E)

Ans: D

Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation Section: 4.16, 4.17, 7.13Difficulty Level: Easy

77. Upon catalytic hydrogenation, a compound C6H6 absorbs four moles of hydrogen. Select a structure for C6H6.

I II III IV V

A) I, IIB) IIIC) II, IIID) IV, VE) I, IV, V

Ans: D

435


78.

Given: One can conclude that X has:

A) no rings and no double bonds.B) no rings and one double bond.C) one ring and one double bond.D) two rings and no double bonds.E) one triple bond.

Ans: C


79. On hydrogenation, a compound C9H12 absorbs 2 mol of hydrogen. Which of the following is a possible structure for the compound?


Ans: D

Topic: Alkene Synthesis

436

Section: 7.10A, 7.13Difficulty Level: Medium

80. What is the major product for the following reaction sequence?1a. NaNH2 (excess) mineral oil, heat1b. NH4Cl

2. H2 (excess), Pd/CCl

Cl

A)

B) C

C)

D)

E) None of the aboveAns: E

Topic: Alkene/Alkyne Reactions, Reaction MechanismsSection: 3.16, 7.10A, 7.13Difficulty Level: Medium

81. Which would be the major product of the following reaction sequence?1a. NaNH2 (excess) mineral oil, heat1b. T3O+

2. H2, Pd/CH

ClCl

A) (CH3CH2)2C=C=CHTB) (CH3CH2)2C=C=CH2

C) (CH3CH2)2CHCCTD) (CH3CH2)2CHCH=CHTE) None of the above

Ans: E


437

Section: 7.11, 7.12, 7.13Difficulty Level: Medium

82. What is the major product for the following reaction sequence?1a. NaNH2, NH3 (liq.)1b. CH3CH2CH2Br

2. H2 (excess), Pd/C

H

H

A)B)C)D) N

HE) None of the above

Ans: B



2. H2 (excess), Pd/C

A)B) CH3CH2CH2Br

C)D)


438

Topic: Alkene Reactions, Reaction MechanismsSection: 4.16, 7.14ADifficulty Level: Medium

84. Which would be the major product of the following reaction?


Ans: A

Topic: Alkene/Alkyne Reactions, Reaction Mechanisms

439

Section: 7.6, 7.14ADifficulty Level: Medium

85. Which would be the major product of the following reaction sequence?

1. EtOH, EtONa

2. D2, Pd/CBr

A)

B)

C)

H

D

D

D)

D

H

D

E)

D

DAns: C

Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms

440


86. Which is not a satisfactory procedure for the synthesis of 3-methyl-1-butene?A) (CH3)2CHCCH3 + conc. H2SO4 B) (CH3)2CHCCH + Li/liq.NH3

C) (CH3)2CHCH2CH2Br + CH3ONa/CH3OHD) (CH3)2CHCHBrCH3 + (CH3)3COK/(CH3)3COHE) (CH3)2CHCCH + H2/Ni2B (P-2)

Ans: A

Topic: Alkene SynthesisSection: 7.10, 7.15Difficulty Level: Medium

87. What is the major product for the following reaction sequence?1. NaNH2 (excess) mineral oil, heat

2. H2, Pd/CaCO3 quinolineBr

Br

A)B)C)D)

E)

Ans: D


441

Section: 7.10A, 7.15Difficulty Level: Medium

88. What is the major product for the following reaction sequence?1a. NaNH2 (excess) mineral oil, heat1b. NH4Cl

2. H2, P-2Cl

Cl

A)

B) C

C)

D)




2a. Li, CH3CH2NH22b. NH4Cl

H

H

A)B)C)D) N


Ans: C

Topic: Alkene SynthesisSection: 7.11, 7.12, 7.15

442

Difficulty Level: Medium


2. H2, Pd/CaCO3 quinoline

H

H

A)B)C)D) N


Ans: C



2a. Li, CH3CH2NH22b. NH4Cl

A)B) CH3CH2CH2Br

C)D)


Topic: Alkene SynthesisSection: 7.11, 7.12, 7.15

443


92. What is the major product for the following reaction sequence?1a. n-BuLi, THF1b. CH3CH2CH2Br

2. H2, P-2

A)B) CH3CH2CH2Br

C)D)


Topic: Alkene Synthesis, Nomenclature, Reaction MechanismsSection: 7.6, 7.7, 7.13, 7.15Difficulty Level: Easy

93. Which of these is the most satisfactory method for the preparation of cis-2-pentene?A) CH3CHBrCH2CH2CH3 + (CH3)3COK/(CH3)3COHB) CH3CCCH2CH3 + H2, PtC) CH3CCCH2CH3 + H2, Ni2B (P-2)D) CH3CCCH2CH3 + Li/liq. NH3

E) CH3CH2CHBrCH2CH3 + CH3CH2ONa/CH3CH2OHAns: C

Topic: Alkyne Synthesis, Nomenclature, Reaction MechanismsSection: 7.6, 7.13, 7.15

444

Difficulty Level: Easy

94. Which reaction would not be a method for preparing 5-methyl-1-hexyne?A)

B)

C)

D)

E)

Ans: C

Topic: Alkyne Reduction, Nomenclature, Reaction MechanismsSection: 7.13, 7.15Difficulty Level: Easy

95. Which of the following reductions of an alkyne is NOT correct?A) 2-Pentyne + 2H2/Pt pentaneB) 2-Pentyne + H2/Ni2B Z-2-PenteneC) 2-Pentyne + Li/NH3(l) Z-2-PenteneD) All of the above are correct.E) None of the above is correct.

Ans: C

Topic: Alkyne Synthesis, Catalytic hydrogenationSection: 7.11, 7.15A

445


96. The structure of the product, C, of the following sequence of reactions would be:

A)

B)

C)

D)

E)

Ans: A

Topic: Alkene/Alkyne Reactions, Reaction MechanismsSection: 7.13, 7.15A

446


97. Which would be the major product of the following reaction sequence?1. D2, Pd/CaCO3 quinoline

2. H2, Ni

A)

D

D

B)

D

D

C)

D

DD)

E) None of the aboveAns: B

Topic: Alkene/Alkyne Reactions, Reaction MechanismsSection: 6.5, 6.16, 7.11, 7.15A

447

Difficulty Level: Hard

98. Which would be the major product of the following reaction sequence?1a. NaNH2, NH3 (liq.)1b. CH2=CHCH2Br

2. D2, P-2

A)

D

DB)

D D

D D H D

D

HH

C) D

DD)


Topic: Dissolving Metal Reduction; trans-hydrogenationSection: 7.15B

448

Difficulty Level: Easy

99. The structure of the product obtained from 2-butyne and Li/C2H5NH2 is:A)

B)

C)

D)

E)

Ans: A

SHORT ANSWER QUESTIONS

449

Topic: General InformationSection: 7.6BDifficulty Level: Easy

100. When an elimination reaction gives the most stable alkene as the major product, we say that the elimination follows ________________'s rule.Ans: Zaitsev

Topic: General InformationSection: 7.6CDifficulty Level: Easy

101. When an elimination reaction gives the less substituted alkene as the major product, we say that the elimination follows ________________'s rule.Ans: Hofmann

Topic: General InformationSection: 7.7Difficulty Level: Easy

102. In a dehydration reaction, the leaving group is _______________.Ans: a molecule of water


103. Dehydration of alcohols requires a __________________ catalyst.Ans: strong acid

Topic: General InformationSection: 7.8Difficulty Level: Medium

104. Carbocations have three options available for further reaction. These options include reaction with a nucleophile, loss of a beta proton to give an alkene, and ________________.Ans: rearrangement

450


105. Alkynes can be produced from either __________________ or _________________ dihalides.Ans: vicinal/geminal


106. In hydrogenation reactions, both hydrogen atoms add to the pi system from the same face of the molecule. This is an example of a(n) _________ addition.Ans: syn

Topic: Alkene HydrogenationSection: 7.14Difficulty Level: Easy

107. How will you prepare cis-1,2-dimethylcyclohexane from 1,2-dimethylcyclohexene?Ans: Catalytic hydrogenation with H2, Ni (or Pt/Pd)


108. Syn hydrogenation of an alkyne will produce a _________ alkene.Ans: Cis / Z


109. Conversion of alkynes to E-alkenes (trans-alkenes) can be accomplished via a __________________ reaction.Ans: dissolving metal reduction

Topic: Alkyne Reduction

451

Section: 7.15Difficulty Level: Medium

110. How will you prepare trans-2-heptene from 2-heptyne?Ans: Dissolving metal reduction with metallic Na in NH3(l).

Topic: Nomenclature, StereochemistrySection: 4.3, 4.5, 5.7, 7.2Difficulty Level: Hard

111. Draw the structures of all stereoisomers of 2-chloro-4-methyl-3-hexene, clearly showing all stereochemical details, using appropriate 3-D representations (dash-wedge, etc.) as relevant.Ans:

Topic: Alkene Nomenclature, Relative Stability Section: 4.5, 7.3Difficulty Level: Hard

112. The ambiguous name dimethylcyclopentene does not clearly distinguish between several structures. a) Draw the structures of all constitutional isomers corresponding to this name. b) Indicate which of these is likely to be the most stable, i.e, have the smallest heat of combustion, justifying your rationale briefly. c) Which of these structures represents an achiral molecule?Ans: a)

b) Structure I is likely to be the most stable, because it is a tetra-substituted alkene: II, IV and V are tri-substituted; III and VI are di-substituted.c) Structure I is achiral

Topic: Carbocation Rearrangement, Alkene Synthesis, Dehydration MechanismSection: 7.7

452


113. Provide a mechanistic explanation for the formation of the observed products in the following reaction.

Ans:

OH2+

OH O

H

H

H

O

H

H

[-H2O]

OH2 O

H

H

O

H

H

H

:

::

:

::

:

:

:

rearrangement

:

1)

2)

3a)

HH

O

H

H O

H

H

H

:

: :3b)

Both

H HH

Topic: Nomenclature, Multistep SynthesisSection: 4.16, 7.7Difficulty Level: Hard

114. Propose a two-step synthetic strategy for the synthesis of 2-methylhexane from 5-methyl-2-hexanol.Ans:

Step 1:Acid-catalyzed dehydration of 5-methyl-2-hexanol to yield an isomeric mixture of 5-methyl-1-hexene and 5-methyl-2-hexene Step 2:Catalytic hydrogenation of the double bond with H2, Ni to yield the desired 2-methylhexane

Topic: Carbocation Stability, RearrangementSection: 7.8

453


115. What “new”, more stable, carbocation(s) may be formed when the following carbocation undergoes spontaneous rearrangement?

Ans:

via a Methyl (methide) shift via a Hydrogen (hydride) shift

Topic: Alkyne Synthesis, Acid-Base reactions Section: 7.10Difficulty Level: Medium

116. Complete the following reaction sequence, providing a brief rationale for your answer.

Ans: O ClCl

(-2HCl)I II

NaH3O+

III

3 NaNH2, mineral oil, heat

:PCl5

Reaction with PCl5 would afford a geminal dihalide I, which would undergo E2 elimination when heated, losing 2 moles of HCl to afford the alkyne III. However, since III is a terminal alkyne, it has a hydrogen atom that is labile in presence of NaNH2; hence, an extra mole equivalent of the base is required to ensure complete reaction and convert all of the initially formed III into the sodium alkynide intermediate, II; this, upon acidification, affords the final alkyne product III.

Topic: Nomenclature, Index of Hydrogen Deficiency, IR Spectroscopy, Catalytic HydrogenationSection: 2.16, 7.13

454


117. The IR spectrum of an unknown substance Q, C9H16, is found to have distinct peaks at 3310 cm-1 and 2140 cm-1. Treatment of Q with excess H2 in presence of Raney Ni affords nearly quantitative yields of 2,3-dimethylheptane. Propose a reasonable structure for Q, based on the above information, briefly explaining your rationale. Also give its IUPAC name.Ans:

IR: 2140, 3310 cm-1

excess H2

Ni

2,3-dimethylheptane

Substance Q: 5,6-dimethyl-1-heptyne

H

The Index of Hydrogen deficiency of Q is 2 (compared with C9H20). The IR data suggests that Q is a terminal alkyne; thus, there must be no rings in its structure. The catalytic hydrogenation data provides further details of the carbon skeleton. Due to the specific substitution pattern in this carbon skeleton, there is only one possible position for a terminal triple bond. Thus, the structure given above is consistent with all of the given information.IUPAC Name: 5,6-dimethyl-1-heptyne

Topic: Nomenclature, Multistep Synthesis

455


118. Propose a reasonable synthetic strategy for the synthesis of trans-6-methyl-3-heptene from 4-methyl-1-pentyne.Ans: NaNH2

NH3 (l)

:Na+

Li, NH3(l)

CH3CH2Br

Step 1:Add NaNH2/NH3(l) to selectively deprotonate the alkyne hydrogen.Step 2:Add ethyl iodide to give 6-methyl-3-pentyne by an SN2 process.Step 3:Add Na(s)/NH3(l) to give the desired trans-alkene by dissolving metal reduction.

Topic: Alkyne Synthesis, Alkyne HydrogenationSection: 7.11, 7.12, 7.15ADifficulty Level: Medium

119. Complete the following reaction, giving structural details of all intermediates as well as the final product.

Ans:

456

Chapter 7

Documents

dissolving

general information

ii iii iv

alkyne synthesis

6b difficulty

15a difficulty

14a difficulty

6c difficulty