Chapter 7 e5d6f
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Chapter Seven MULTIPLE CHOICE QUESTIONS Topic: Nomenclature Section: 4.3, 4.5, 7.2 Difficulty Level: Easy 1. The correct IUPAC name for the following compound is: Br
A) B) C) D) E)
2-Bromo-4-methylenehexane 2-(2-Bromopropyl)-1-butene 4-Bromo-2-ethyl-1-pentene 2-Bromo-4-ethyl-1-pentene 2-Bromo-4-ethyl-4-pentene Ans: C
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 2. Name the following compound: OCH3
A) B) C) D) E)
(cis)-3-methoxyhex-3-ene (Z)-4-methoxyhex-4-ene (Z)-3-methoxyhex-3-ene (E)-3-methoxyhex-3-ene 3-methoxyhex-3-ene Ans: C
130
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 3. Name the following compound: HO
A) B) C) D) E)
(E)-4-phenyl-4-methylbut-3-en-1-ol (E)-4-phenylpent-3-en-1-ol (Z)-4-phenylpent-3-en-1-ol (Z)-4-phenyl-4-methylbut-3-en-1-ol (E)-4-benzylpent-3-en-1-ol Ans: B
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 4. Which structure represents (Z)-4-bromohexa-1,3-diene? A) Br
B) Br
C) Br
D)
Br
E) None of the above Ans: C
131
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 5. Which structure represents (E)-1-bromo-2-methylhex-2-ene? A) Br B) Br
C) Br
Br
D)
E) None of the above Ans: A Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 6. Which structure represents (Z)-1,4-dichlorohex-3-en-1-yne? A) Cl Cl Cl
B) C)
Cl
Cl Cl
D)
Cl
Cl
E) None of the above Ans: B
132
Topic: Nomenclature Section: 4.5, 7.2 Difficulty Level: Easy 7. A correct IUPAC name for the following compound is:
A) B) C) D) E)
3,3,5-trimethyl-2-hexene 3-isobutyl-3-isopropyl-2-propene 3-isobutyl-4-methyl-2-pentene 3-(1-methylethyl)-5-methyl-2-hexene None of the above Ans: E
Topic: Nomenclature Section: 4.5, 7.2 Difficulty Level: Easy 8. The correct IUPAC name for the following compound is:
A) B) C) D) E)
4,5-Dimethyl-3-propyl-2-hexene 4,5-Dimethyl-3-propyl-1-hexene 3-(2,3-Dimethylpropyl)-1-hexene 2,3-Dimethyl-4-isopropyl-5-hexene 2,3-Dimethyl-4-propyl-5-hexene Ans: B
133
Topic: Nomenclature Section: 4.5, 7.2 Difficulty Level: Easy 9. Select the structure of 4–ethyl-2,3-dimethyl-2-heptene. A)
B)
C)
D)
E)
Ans: B Topic: Nomenclature Section: 4.5, 7.2 Difficulty Level: Medium 10. The correct IUPAC name for the following compound is: Cl
Br
A) B) C) D) E)
(E)-2-Bromo-3-chloro-5-methyl-2-hexene (E)-2-Bromo-3-chloro-5-methyl-3-hexene (Z)-2-Bromo-3-chloro-5-methyl-3-hexene (Z)-2-Bromo-3-chloro-5-methyl-2-hexene (E)-2-Methyl-5-bromo-4-chloro-4-hexene Ans: A
134
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty Level: Medium 11. Name the following compound: Br
A) B) C) D) E)
(S,Z)-3-bromo-4-methylhex-2-ene (S)-3-bromo-4-methylhex-2-ene (S,Z)-4-bromo-3-methylhex-4-ene (S,E)-3-bromo-4-methylhex-2-ene (R,E)-3-bromo-4-methylhex-2-ene Ans: A
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty Level: Medium 12. Name the following compound: Br Br
A) B) C) D) E)
(S,E)-2,4-dibromo-3-methylpent-2-ene (R,Z)-2,4-dibromo-3-methylpent-2-ene (R,E)-2,4-dibromo-3-methylpent-3-ene (S,E)-2,4-dibromo-3-methylpent-3-ene (R,E)-2,4-dibromo-3-methylpent-2-ene Ans: E
135
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty Level: Hard 13. Name the following compound:
OH
A) B) C) D) E)
(R,Z)-5-phenyloct-5-en-3-ol (R,Z)-5-benzyloct-5-en-3-ol (R,E)-5-phenyloct-5-en-3-ol (R,E)-5-benzyloct-5-en-3-ol (R,E)-5-benzyloct-3-en-6-ol Ans: B
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty Level: Hard 14. Which structure represents (R,Z)-5-methylhept-2-ene? A)
B) C) D)
E) None of the above Ans: D
136
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 4.6, 5.7, 7.2 Difficulty Level: Medium 15. Name the following compound: Cl
A) B) C) D) E)
(S,E)-3-chlorohex-4-en-1-yne (R,E)-3-chlorohex-2-en-5-yne (S,E)-3-chlorohex-2-en-5-yne (R,E)-3-chlorohex-4-en-1-yne (R,E)-3-chloropent-4-en-1-yne Ans: D
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty Level: Easy 16. Which molecule would have the lowest heat of hydrogenation?
I A) B) C) D) E)
II
III
IV
I II III IV V Ans: A
137
V
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty Level: Easy 17. Heats of hydrogenation data would be useful in comparing the relative stabilities of which of the following substances?
I II III IV V I, II, III III, IV I, II, V 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
A) B) C) D)
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty Level: Easy 18. Which alkene would liberate the most heat per mole when subjected to catalytic hydrogenation? A) B) C) D) E) Ans: A
138
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty Level: Easy 19. Which alkene is most stable?
I A) B) C) D) E)
II
III
IV
V
I II III IV V Ans: A
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty 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
139
Topic: Alkene Synthesis, Reaction Mechanisms Section: 7.6 Difficulty Level: Easy 21. Which product (or products) would be formed in appreciable amount(s) when trans-1bromo-2-methylcyclohexane undergoes dehydrohalogenation upon treatment with sodium ethoxide in ethanol?
I A) B) C) D) E)
II
III
IV
I II III IV More than one of these Ans: B
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 22. Your task is to convert 2-bromobutane to 1-butene in highest yield. Which reagents would you use? A) KOH/H2O B) KOH/CH3OH C) CH3ONa/CH3OH D) CH3CH2ONa/CH3CH2OH E) (CH3)3COK/(CH3)3COH Ans: E
140
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 23. What is the major product for the following reaction? EtOH, EtONa OTs
A) B) C) D) E)
heat
CH3CH2(CH3)C=CHCH3 CH3CH2(CH3)CHCH=CH2 CH3CH2(CH3)CHCH(OCH2CH3)CH3 None of the above No reaction Ans: A
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 24. What is the major product for the following reaction? t-BuOH, t-BuOK Cl
A) Ot-Bu
B) C) D) E) Ans: E
141
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 25. What is the major product for the following reaction? I
t-BuOH, t-BuOK
A)
B)
C)
D)
E) None of the above Ans: D
142
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 26. What is the major product for the following reaction? EtONa, EtOH I
heat
A)
B)
C)
D)
E) None of the above Ans: A
143
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 27. What is the major product for the following reaction? Cl EtOH, EtONa heat
A)
B)
C)
D)
E)
Ans: A
144
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 28. What is the major product for the following reaction? Br
t-BuOK, t-BuOH
A)
B)
C)
D)
E)
Ans: E
145
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Medium 29. What is the major product for the following reaction? EtONa, EtOH Br
heat
A)
B)
C)
D)
E) More than one of the above Ans: C
146
Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms Section: 7.6 Difficulty 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 Synthesis Section: 7.6 Difficulty Level: Hard 31. What is the major product for the following reaction? EtOH, EtONa Br
heat
A) OEt
B) C) D) E) Ans: C
147
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Hard 32. What is the major product for the following reaction? EtOH, EtONa Cl
heat
A) OEt
B) C) D) E) Ans: B
148
Topic: Alkene Synthesis Section: 6.5, 7.6 Difficulty Level: Medium 33. What is the major product for the following reaction? 1. NaI, acetone OTs
2. t-BuOH, t-BuOK
A) B) C) D) E) Ans: C
149
Topic: Alkene Synthesis Section: 6.5, 7.6 Difficulty Level: Hard 34. What is the major product for the following reaction? 1. NaI, acetone Cl
2. t-BuOH, t-BuOK
A) B) C) D) E) Ans: D
150
Topic: Alkene Synthesis Section: 6.5, 7.6 Difficulty Level: Hard 35. What is the major product for the following reaction? 1. NaI, acetone Cl
2. NaOH, EtOH, heat
A) B) C) D) E) Ans: C
151
Topic: Alkene Synthesis Section: 6.5, 7.6 Difficulty Level: Hard 36. What is the major product for the following reaction? 1. NaI, acetone Br
2. EtONa, EtOH, heat
A) B) C) D) E) Ans: B
152
Topic: Alkene Synthesis, Reaction Mechanisms Section: 6.5, 6.16, 7.6 Difficulty Level: Medium 37. Which compound listed below would you expect to be the major product when 2-bromo2-methylbutane is refluxed with KOH/ethanol? A) OH B) O
C) D) E) Ans: D Topic: Alkene Synthesis Section: 7.6B Difficulty 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 β-hydrogen and leaving group can assume an antiperiplanar 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
153
Topic: Alkene Synthesis Section: 7.6C Difficulty 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 Mechanisms Section: 7.6C Difficulty Level: Easy 40. What is the major product of the reaction, (CH3)3COK ? (CH3)3COH heat Br A) B) C) D) E)
(CH3)2C=C(CH3)2 (CH3)3C–CH=CH2 (CH3)2C=CHCH3 (CH3)2C=CHCH2CH3 None of these Ans: B
154
Topic: Alkene Synthesis, Reaction Mechanisms Section: 7.6C Difficulty Level: Easy 41. Which compound would be the major product? Br (CH3)3COK ? (CH3)3COH heat O
A)
B) C) OH
D) E) Ans: E
155
Topic: Carbocation Stability, Rearrangement Section: 7.7 Difficulty Level: Easy 42. A) B) C) D) E)
Which statement(s) is/are true of acid-catalyzed alcohol dehydrations? Protonation of the alcohol is a fast step. Formation of a carbocation from the protonated alcohol is a slow step. Rearrangements of less stable carbocations to more stable carbocations are common. Loss of a proton by the carbocation is a fast step. All of the above Ans: E
Topic: Alkene Synthesis, Reaction Mechanisms Section: 7.7 Difficulty Level: Easy 43. Which product(s) would be produced by acid-catalyzed dehydration of 2-methyl-2pentanol? A) B)
and
C)
and
D) E) O
Ans: B
156
Topic: Alkene Synthesis; Alcohol Dehydration Section: 7.7 Difficulty Level: Easy 44. Which one of the following alcohols would dehydrate most rapidly when treated with sulfuric acid? OH
OH
I
OH
II
III OH
OH
IV A) B) C) D) E)
V
I II III IV V Ans: B
157
Topic: Alkene Synthesis; Alcohol Dehydration Section: 7.7 Difficulty Level: Easy 45. Which mechanistic step in the acid-catalyzed dehydration of 3,3-dimethyl-2-butanol is the rate determining step? A) Step 1: +
H3O+
OH
+
H2O
OH2
B) Step 2: +
H2O
OH2
C) Step 3:
D) Step 4a: +
H2O
+
H3O+
+
H 2O
+
H3O+
E) Step 4b:
Ans: B
158
Topic: Alkene Synthesis; Alcohol Dehydration Section: 7.7 Difficulty Level: Easy 46. Which alcohol would be most easily dehydrated? CH3 A) CH3CH2CCH2CH3 OH CH3
B)
CH3CH2CHCHCH3 OH CH3
C)
CH3CH2CHCH2CH2OH CH3 D) HOCH2CHCH2CH2CH3 CH2OH E) CH3CH2CHCH2CH3 Ans: A Topic: Alkene Synthesis; Alcohol Dehydration Section: 7.7 Difficulty Level: Easy 47. Which alcohol would be most easily dehydrated?
OH
OH
I
OH
II
III OH
OH
IV A) B) C) D) E)
V
I II III IV V Ans: B
159
Topic: Carbocation Stability Section: 7.7 Difficulty Level: Medium 48. Which alcohol would initially produce the most stable carbocation when treated with concentrated H2SO4? A) OH B)
OH
C) OH
D) HO
E) HO
Ans: A Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.7 Difficulty 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
160
Topic: Carbocation Stability, Rearrangement Section: 6.11B, 7.7B Difficulty Level: Easy 50. Which of the following carbocations would NOT be likely to undergo rearrangement? A) CH3CHCHCH3 CH3 CH3 B) CH3CHCCH3 CH3
C) D)
CH3 CH3CCH2CH3 CH3
CH3CHCH2 CH3 E) CH3CCHCH2CH3 CH3 Ans: C Topic: Carbocation Stability, Rearrangement Section: 7.8 Difficulty Level: Hard 51. Neopentyl alcohol, (CH3)3CCH2OH, cannot be dehydrated to an alkene without rearrangement. What is the chief product of dehydration?
I
II
IV A) B) C) D) E)
III
V
I II III IV V Ans: B
161
Topic: Carbocation Stability, Rearrangement Section: 5.12, 6.10, 6.17, 7.8 Difficulty Level: Medium 52. What is the major product of the reaction between methanol and (2R,3S)-2-bromo-3methylpentane at room temperature? A) B)
OCH3
C) D) H3CO
E) Both A) and C) Ans: D Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Easy 53. A) B) C) D) E)
Rearrangements are likely to occur in which of the following reaction types? SN1 reactions SN2 reactions E1 reactions E2 reactions Both SN1 and E1 reactions Ans: E
162
Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Easy 54. What is the major product of the reaction of the following reaction? I
A)
B)
ethanol, 20 oC
CH3CH2O
OCH2CH3
C)
D)
E) More than one of the above Ans: A
163
Topic: Alkene Synthesis Section: 6.10, 6.17, 7.8 Difficulty Level: Easy 55. What is the major product for the following reaction? Br
EtOH, heat
A)
B)
C)
D)
E) More than one of the above Ans: E
164
Topic: Alkene Synthesis Section: 6.10, 6.17, 7.8 Difficulty Level: Medium 56. What is the major product for the following reaction? I
EtOH, heat
A)
B)
C)
D)
E) None of the above Ans: C
165
Topic: Alkene Synthesis Section: 6.10, 6.17, 7.8 Difficulty Level: Medium 57. What is the major product for the following reaction? Cl
EtOH, heat
A)
B)
C)
D)
E)
Ans: D
166
Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Hard 58. What is the major product of the reaction of the following reaction? Cl
EtOH, heat
A) B) OEt
C) D)
E)
Ans: D
167
Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Hard 59. What is the major product of the reaction of the following reaction? EtOH, heat OTs
A)
B)
C)
OEt
D)
E) None of the above Ans: A
168
Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Hard 60. What is the major product of the reaction of the following reaction? CH3OH, heat Cl
A) H3CO
B)
C)
D)
E) Ans: E
169
Topic: Carbocation Stability, Rearrangement Section: 4.16, 6.10, 6.17, 7.3, 7.8 Difficulty 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
170
Topic: Alkene Synthesis, Reaction Mechanisms, Carbocation Rearrangements Section: 7.7, 7.8 Difficulty Level: Medium 62. Which alkene would you expect to be the major product of the following dehydration? H2SO4 ?
heat OH
I
IV
A) B) C) D) E)
III
II
V
I II III IV V Ans: C
171
Topic: Alkene Synthesis, Reaction Mechanisms, Carbocation Rearrangements Section: 7.7, 7.8 Difficulty Level: Hard 63. What will be the major product of the following reaction? 85% H3PO4 ? heat OH
A)
B)
C) D)
O
E) Ans: A
172
Topic: Alkene Synthesis, Nomenclature Section: 7.6C, 7.7, 7.10 Difficulty 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) H2SO4 heat
OH
B)
(CH3)3COK, (CH3)3COH heat
Br
C) Br Br
i) 3 NaNH2, mineral oil, heat ii) H3O+
D) All of these E) Answers B) and C) only Ans: B Topic: Alkyne Synthesis Section: 7.11 Difficulty Level: Easy 65. A) B) C) D) E)
Which reaction would yield 2-butyne? − + CH3C≡ C: Na + CH3Br → − + CH3CH2Br + HC≡ C: Na → − + CH3: Na + HC≡ CCH3 → More than one of these None of these Ans: A
173
Topic: Alkyne Synthesis Section: 3.6, 7.11, 7.12 Difficulty Level: Hard 66. Which reaction conditions would not yield 2-butyne from 1-propyne? A) a. EtONa, EtOH b. CH3I B) a. CH3Li, THF b. CH3I C) a. NaNH2, NH3 (liq) b. CH3I
D) a. NaCH2CH3, THF b. CH3I E) More than one of these Ans: A
Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms Section: 7.6, 7.7, 7.11, 7.12 Difficulty Level: Easy 67. Which of the following reactions would yield 2-pentyne? I A) NaNH2 (1 mol) NaNH2
B)
Br
(1 mol)
C)
Br
CH3OH Br
D) E)
Br
HA heat
OH
NaOC2H5 C2H5OH Ans: B
174
Topic: Alkyne Synthesis Section: 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? CH3 A) C2H5 C C C: Na CH3
H3C
I
CH3
B) H3C C C:
Na
C)
C2H5 C Br CH3
NaNH2 ( excess) Br
Br
NH3 (l)
D) More than one of these E) None of these Ans: D Topic: Alkyne Synthesis Section: 7.11, 7.12 Difficulty Level: Easy 69. A) B) C)
Which statement is/are true about acetylide anions? They do not alkylate with secondary alkyl halides. Primary alkyl halides are best suited for alkylation. 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
175
Topic: Alkyne Synthesis Section: 7.11, 7.12 Difficulty Level: Medium 70. Which reaction would not result in alkylation of the acetylide anion? Br A) Li Cl B) Li C)
D)
Li
Br OTs
Li E) None of the above Ans: C
Topic: Alkyne Synthesis Section: 7.11, 7.12 Difficulty Level: Medium 71. Which reaction would not primarily proceed via an SN2 mechanism? Br A) Li Cl B) Li C)
D)
Li
Br OTs
Li E) All of them proceed via SN2 Ans: C
176
Topic: Alkene/Alkyne Reactions, Reaction Mechanisms Section: 3.16, 7.13 Difficulty 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) CH2CH3
B) CH=CHT
C) CH=CH2
D) CH2CH2T
E) None of the above Ans: D Topic: Structure Elucidation Section: 2.16, 4.16, 7.13 Difficulty 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-hexyne B) 5-methyl-2-hexyne C) 5-methyl-1,3-hexadiene D) 5-methyl-1-hexyne E) 2-methyl-1,5-hexadiene Ans: D
Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation 177
Section: 2.16, 4.16, 4.17, 7.13 Difficulty 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, 7.13 Difficulty 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:
I
II
IV A) B) C) D) E)
III
V
I II III IV V Ans: C
Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation 178
Section: 2.16, 4.16, 4.17, 7.13 Difficulty 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 2methylpentane? A) B) C) D) E) Ans: D Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation Section: 4.16, 4.17, 7.13 Difficulty Level: Easy 77. Upon catalytic hydrogenation, a compound C6H6 absorbs four moles of hydrogen. Select a structure for C6H6.
I A) B) C) D) E)
II
III
IV
I, II III II, III IV, V I, IV, V Ans: D
179
V
Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation Section: 4.16, 4.17, 7.13 Difficulty Level: Easy 78.
A) B) C) D) E)
X (C8H14)
H2, Pt
25oC Given: One can conclude that X has: no rings and no double bonds. no rings and one double bond. one ring and one double bond. two rings and no double bonds. one triple bond. Ans: C
Y (C8H16)
Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation Section: 4.16, 4.17, 7.13 Difficulty Level: Easy 79. On hydrogenation, a compound C9H12 absorbs 2 mol of hydrogen. Which of the following is a possible structure for the compound?
I
A) B) C) D) E)
I II III IV V Ans: D
III
II
IV
V
Topic: Alkene Synthesis 180
Section: 7.10A, 7.13 Difficulty Level: Medium 80. What is the major product for the following reaction sequence? 1a. NaNH2 (excess) mineral oil, heat Cl 1b. NH4Cl Cl
2. H2 (excess), Pd/C
A)
B)
C
C) D) E) None of the above Ans: E Topic: Alkene/Alkyne Reactions, Reaction Mechanisms Section: 3.16, 7.10A, 7.13 Difficulty Level: Medium 81. Which would be the major product of the following reaction sequence? 1a. NaNH2 (excess) Cl mineral oil, heat Cl 1b. T3O+ H
2. H2, Pd/C
A) B) C) D) E)
(CH3CH2)2C=C=CHT (CH3CH2)2C=C=CH2 (CH3CH2)2CHCCT (CH3CH2)2CHCH=CHT None of the above Ans: E
Topic: Alkene Synthesis
181
Section: 7.11, 7.12, 7.13 Difficulty Level: Medium 82. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) H 1b. CH3CH2CH2Br H
A) B) C) D)
2. H2 (excess), Pd/C
N H
E) None of the above Ans: B Topic: Alkene Synthesis Section: 7.11, 7.12, 7.13 Difficulty Level: Medium 83. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) 1b. CH3CH2CH2Br 2. H2 (excess), Pd/C A) B) CH3CH2CH2Br C) D) E) None of the above Ans: A
182
Topic: Alkene Reactions, Reaction Mechanisms Section: 4.16, 7.14A Difficulty Level: Medium 84. Which would be the major product of the following reaction?
D2, Ni
?
D
D
D CH3
CH3 H CH3
H
DD
D
I
H
II
III
CH3 DH D
D CH3
D H
IV A) B) C) D) E)
V
I II III IV V Ans: A
Topic: Alkene/Alkyne Reactions, Reaction Mechanisms
183
Section: 7.6, 7.14A Difficulty Level: Medium 85. Which would be the major product of the following reaction sequence? 1. EtOH, EtONa 2. D2, Pd/C
Br
A)
B)
C) D D H
D) D H D
E)
D D
Ans: C
Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms 184
Section: 7.6, 7.7, 7.15 Difficulty Level: Medium 86. A) B) C) D) E)
Which is not a satisfactory procedure for the synthesis of 3-methyl-1-butene? (CH3)2CHCΗΟΗCH3 + conc. H2SO4 (CH3)2CHC≡ CH + Li/liq.NH3 (CH3)2CHCH2CH2Br + CH3ONa/CH3OH (CH3)2CHCHBrCH3 + (CH3)3COK/(CH3)3COH (CH3)2CHC≡ CH + H2/Ni2B (P-2) Ans: A
Topic: Alkene Synthesis Section: 7.10, 7.15 Difficulty Level: Medium 87. What is the major product for the following reaction sequence? 1. NaNH2 (excess) Br mineral oil, heat Br
2. H2, Pd/CaCO3 quinoline
A) B) C) D) E) Ans: D
185
Topic: Alkene Synthesis Section: 7.10A, 7.15 Difficulty Level: Medium 88. What is the major product for the following reaction sequence? 1a. NaNH2 (excess) mineral oil, heat Cl 1b. NH4Cl Cl
2. H2, P-2
A)
B)
C
C) D) E) None of the above Ans: C Topic: Alkene Synthesis Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 89. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) H 1b. CH3CH2CH2Br H
A) B) C) D)
2a. Li, CH3CH2NH2 2b. NH4Cl
N H
E) None of the above Ans: C Topic: Alkene Synthesis 186
Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 90. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) H 1b. CH3CH2CH2Br H
A) B) C) D)
2. H2, Pd/CaCO3 quinoline
N H
E) None of the above Ans: C Topic: Alkene Synthesis Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 91. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) 1b. CH3CH2CH2Br 2a. Li, CH3CH2NH2 2b. NH4Cl A) B) CH3CH2CH2Br C) D) E) None of the above Ans: C
Topic: Alkene Synthesis 187
Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 92. What is the major product for the following reaction sequence? 1a. n-BuLi, THF 1b. CH3CH2CH2Br 2. H2, P-2 A) B) CH3CH2CH2Br C) D) E) None of the above Ans: D Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms Section: 7.6, 7.7, 7.13, 7.15 Difficulty Level: Easy 93. A) B) C) D) E)
Which of these is the most satisfactory method for the preparation of cis-2-pentene? CH3CHBrCH2CH2CH3 + (CH3)3COK/(CH3)3COH CH3C≡ CCH2CH3 + H2, Pt CH3C≡ CCH2CH3 + H2, Ni2B (P-2) CH3C≡ CCH2CH3 + Li/liq. NH3 CH3CH2CHBrCH2CH3 + CH3CH2ONa/CH3CH2OH Ans: C
Topic: Alkyne Synthesis, Nomenclature, Reaction Mechanisms
188
Section: 7.6, 7.13, 7.15 Difficulty Level: Easy 94. Which reaction would not be a method for preparing 5-methyl-1-hexyne? A) 1) NaNH2 (2 mol), liq NH3
Br
2) NH4+
B) HC
CNa
+ Cl
C) Li
D)
CH
1) NaNH2 (3 mol), liq NH3
Br Br
E)
+ HC
Br
Br
2) NH4+ 1) NaNH2 (3 mol), liq NH3
2) NH4+
Ans: C Topic: Alkyne Reduction, Nomenclature, Reaction Mechanisms Section: 7.13, 7.15 Difficulty Level: Easy 95. A) B) C) D) E)
Which of the following reductions of an alkyne is NOT correct? 2-Pentyne + 2H2/Pt pentane 2-Pentyne + H2/Ni2B Z-2-Pentene 2-Pentyne + Li/NH3(l) Z-2-Pentene All of the above are correct. None of the above is correct. Ans: C
Topic: Alkyne Synthesis, Catalytic hydrogenation 189
Section: 7.11, 7.15A Difficulty Level: Medium 96. The structure of the product, C, of the following sequence of reactions would be: NaNH2 NH3(l)
A
CH3CH2Br
A) B) C) Br
D)
E)
Ans: A
Topic: Alkene/Alkyne Reactions, Reaction Mechanisms
190
B
H2 Ni2B [P-2]
C
Section: 7.13, 7.15A Difficulty Level: Medium 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 D
D) E) None of the above Ans: B
Topic: Alkene/Alkyne Reactions, Reaction Mechanisms
191
Section: 6.5, 6.16, 7.11, 7.15A 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 D
B)
D
D
H D D
D
D
C)
H
H
D
D
D) E) None of the above Ans: A
Topic: Dissolving Metal Reduction; trans-hydrogenation 192
Section: 7.15B Difficulty Level: Easy 99. The structure of the product obtained from 2-butyne and Li/C2H5NH2 is: A) B) C)
HN
D) NH
E) Ans: A
193
SHORT ANSWER QUESTIONS Topic: General Information Section: 7.6B Difficulty 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 Information Section: 7.6C Difficulty 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 Information Section: 7.7 Difficulty Level: Easy 102. In a dehydration reaction, the leaving group is _______________. Ans: a molecule of water Topic: General Information Section: 7.7 Difficulty Level: Easy 103. Dehydration of alcohols requires a __________________ catalyst. Ans: strong acid Topic: General Information Section: 7.8 Difficulty 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
194
Topic: General Information Section: 7.10 Difficulty Level: Medium 105. Alkynes can be produced from either __________________ or _________________ dihalides. Ans: vicinal/geminal Topic: General Information Section: 7.14 Difficulty Level: Easy 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 Hydrogenation Section: 7.14 Difficulty Level: Easy 107. How will you prepare cis-1,2-dimethylcyclohexane from 1,2-dimethylcyclohexene? Ans: Catalytic hydrogenation with H2, Ni (or Pt/Pd) H2, Ni
Topic: General Information Section: 7.15 Difficulty Level: Easy 108. Syn hydrogenation of an alkyne will produce a _________ alkene. Ans: Cis / Z Topic: General Information Section: 7.15 Difficulty Level: Medium 109. Conversion of alkynes to E-alkenes (trans-alkenes) can be accomplished via a __________________ reaction. Ans: dissolving metal reduction
195
Topic: Alkyne Reduction Section: 7.15 Difficulty Level: Medium 110. How will you prepare trans-2-heptene from 2-heptyne? Ans: Dissolving metal reduction with metallic Na in NH3(l). Na, NH3 (l)
Topic: Nomenclature, Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty 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. 2-chloro-4-methyl-3-hexene Ans: Cl
H
H
(2R, 3E)
Cl
Cl
(2S, 3E)
H
H
(2R, 3Z)
Cl
(2S, 3Z)
Topic: Alkene Nomenclature, Relative Stability Section: 4.5, 7.3 Difficulty 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) dimethylcyclopentene
I
II
III
IV
V
VI
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 Mechanism 196
Section: 7.7 Difficulty Level: Medium 113. Provide a mechanistic explanation for the formation of the observed products in the following reaction. H3O+ OH heat Ans:
H
:
:O H
OH2
:O H
:
: :
OH
1)
H
OH2+
rearrangement [-H2O]
:
2)
H
H
:
3a)
:O H H
Both H
H
H
H
H
H
H
:
3b)
:O H
:O H H
:O H H
Topic: Nomenclature, Multistep Synthesis Section: 4.16, 7.7 Difficulty Level: Hard 114. Propose a two-step synthetic strategy for the synthesis of 2-methylhexane from 5-methyl2-hexanol. OH Ans: H3O+ H2 + Ni heat 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 2methylhexane Topic: Carbocation Stability, Rearrangement 197
Section: 7.8 Difficulty Level: Medium 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: 7.10 Difficulty Level: Medium 116. Complete the following reaction sequence, providing a brief rationale for your answer. O
i) PCl5
?
ii) 3 NaNH2, mineral oil, heat iii) H3O+ Ans:
O
Cl
: Na H3 O+ 3 NaNH2, mineral oil, heat (-2HCl) II III I 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.
PCl5
Cl
Topic: Nomenclature, Index of Hydrogen Deficiency, IR Spectroscopy, Catalytic Hydrogenation Section: 2.16, 7.13 198
Difficulty Level: Medium 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: H excess H2 Ni IR: 2140, 3310 cm-1
2,3-dimethylheptane
Substance Q: 5,6dimethyl-1-heptyne
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
199
Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 118. Propose a reasonable synthetic strategy for the synthesis of trans-6-methyl-3-heptene from 4-methyl-1-pentyne. Ans: Na+: CH3CH2Br NaNH2 NH3 (l) Li, NH3(l)
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 Hydrogenation Section: 7.11, 7.12, 7.15A Difficulty Level: Medium 119. Complete the following reaction, giving structural details of all intermediates as well as the final product. ?
:
Ans:
1) NaNH2, NH3 (l) 2) CH3CH2CH2Br 3) H2, Lindlar catalyst NaNH2 NH3 (l)
Na
CH3CH2CH2Br H2 Lindlar catalyst
200
A) B) C) D) E)
2-Bromo-4-methylenehexane 2-(2-Bromopropyl)-1-butene 4-Bromo-2-ethyl-1-pentene 2-Bromo-4-ethyl-1-pentene 2-Bromo-4-ethyl-4-pentene Ans: C
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 2. Name the following compound: OCH3
A) B) C) D) E)
(cis)-3-methoxyhex-3-ene (Z)-4-methoxyhex-4-ene (Z)-3-methoxyhex-3-ene (E)-3-methoxyhex-3-ene 3-methoxyhex-3-ene Ans: C
130
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 3. Name the following compound: HO
A) B) C) D) E)
(E)-4-phenyl-4-methylbut-3-en-1-ol (E)-4-phenylpent-3-en-1-ol (Z)-4-phenylpent-3-en-1-ol (Z)-4-phenyl-4-methylbut-3-en-1-ol (E)-4-benzylpent-3-en-1-ol Ans: B
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 4. Which structure represents (Z)-4-bromohexa-1,3-diene? A) Br
B) Br
C) Br
D)
Br
E) None of the above Ans: C
131
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 5. Which structure represents (E)-1-bromo-2-methylhex-2-ene? A) Br B) Br
C) Br
Br
D)
E) None of the above Ans: A Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 7.2 Difficulty Level: Medium 6. Which structure represents (Z)-1,4-dichlorohex-3-en-1-yne? A) Cl Cl Cl
B) C)
Cl
Cl Cl
D)
Cl
Cl
E) None of the above Ans: B
132
Topic: Nomenclature Section: 4.5, 7.2 Difficulty Level: Easy 7. A correct IUPAC name for the following compound is:
A) B) C) D) E)
3,3,5-trimethyl-2-hexene 3-isobutyl-3-isopropyl-2-propene 3-isobutyl-4-methyl-2-pentene 3-(1-methylethyl)-5-methyl-2-hexene None of the above Ans: E
Topic: Nomenclature Section: 4.5, 7.2 Difficulty Level: Easy 8. The correct IUPAC name for the following compound is:
A) B) C) D) E)
4,5-Dimethyl-3-propyl-2-hexene 4,5-Dimethyl-3-propyl-1-hexene 3-(2,3-Dimethylpropyl)-1-hexene 2,3-Dimethyl-4-isopropyl-5-hexene 2,3-Dimethyl-4-propyl-5-hexene Ans: B
133
Topic: Nomenclature Section: 4.5, 7.2 Difficulty Level: Easy 9. Select the structure of 4–ethyl-2,3-dimethyl-2-heptene. A)
B)
C)
D)
E)
Ans: B Topic: Nomenclature Section: 4.5, 7.2 Difficulty Level: Medium 10. The correct IUPAC name for the following compound is: Cl
Br
A) B) C) D) E)
(E)-2-Bromo-3-chloro-5-methyl-2-hexene (E)-2-Bromo-3-chloro-5-methyl-3-hexene (Z)-2-Bromo-3-chloro-5-methyl-3-hexene (Z)-2-Bromo-3-chloro-5-methyl-2-hexene (E)-2-Methyl-5-bromo-4-chloro-4-hexene Ans: A
134
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty Level: Medium 11. Name the following compound: Br
A) B) C) D) E)
(S,Z)-3-bromo-4-methylhex-2-ene (S)-3-bromo-4-methylhex-2-ene (S,Z)-4-bromo-3-methylhex-4-ene (S,E)-3-bromo-4-methylhex-2-ene (R,E)-3-bromo-4-methylhex-2-ene Ans: A
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty Level: Medium 12. Name the following compound: Br Br
A) B) C) D) E)
(S,E)-2,4-dibromo-3-methylpent-2-ene (R,Z)-2,4-dibromo-3-methylpent-2-ene (R,E)-2,4-dibromo-3-methylpent-3-ene (S,E)-2,4-dibromo-3-methylpent-3-ene (R,E)-2,4-dibromo-3-methylpent-2-ene Ans: E
135
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty Level: Hard 13. Name the following compound:
OH
A) B) C) D) E)
(R,Z)-5-phenyloct-5-en-3-ol (R,Z)-5-benzyloct-5-en-3-ol (R,E)-5-phenyloct-5-en-3-ol (R,E)-5-benzyloct-5-en-3-ol (R,E)-5-benzyloct-3-en-6-ol Ans: B
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty Level: Hard 14. Which structure represents (R,Z)-5-methylhept-2-ene? A)
B) C) D)
E) None of the above Ans: D
136
Topic: Nomenclature; Stereochemistry Section: 4.3, 4.5, 4.6, 5.7, 7.2 Difficulty Level: Medium 15. Name the following compound: Cl
A) B) C) D) E)
(S,E)-3-chlorohex-4-en-1-yne (R,E)-3-chlorohex-2-en-5-yne (S,E)-3-chlorohex-2-en-5-yne (R,E)-3-chlorohex-4-en-1-yne (R,E)-3-chloropent-4-en-1-yne Ans: D
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty Level: Easy 16. Which molecule would have the lowest heat of hydrogenation?
I A) B) C) D) E)
II
III
IV
I II III IV V Ans: A
137
V
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty Level: Easy 17. Heats of hydrogenation data would be useful in comparing the relative stabilities of which of the following substances?
I II III IV V I, II, III III, IV I, II, V 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
A) B) C) D)
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty Level: Easy 18. Which alkene would liberate the most heat per mole when subjected to catalytic hydrogenation? A) B) C) D) E) Ans: A
138
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty Level: Easy 19. Which alkene is most stable?
I A) B) C) D) E)
II
III
IV
V
I II III IV V Ans: A
Topic: Alkene Stability, Heats of Hydrogenation and Combustion Section: 7.3 Difficulty 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
139
Topic: Alkene Synthesis, Reaction Mechanisms Section: 7.6 Difficulty Level: Easy 21. Which product (or products) would be formed in appreciable amount(s) when trans-1bromo-2-methylcyclohexane undergoes dehydrohalogenation upon treatment with sodium ethoxide in ethanol?
I A) B) C) D) E)
II
III
IV
I II III IV More than one of these Ans: B
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 22. Your task is to convert 2-bromobutane to 1-butene in highest yield. Which reagents would you use? A) KOH/H2O B) KOH/CH3OH C) CH3ONa/CH3OH D) CH3CH2ONa/CH3CH2OH E) (CH3)3COK/(CH3)3COH Ans: E
140
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 23. What is the major product for the following reaction? EtOH, EtONa OTs
A) B) C) D) E)
heat
CH3CH2(CH3)C=CHCH3 CH3CH2(CH3)CHCH=CH2 CH3CH2(CH3)CHCH(OCH2CH3)CH3 None of the above No reaction Ans: A
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 24. What is the major product for the following reaction? t-BuOH, t-BuOK Cl
A) Ot-Bu
B) C) D) E) Ans: E
141
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 25. What is the major product for the following reaction? I
t-BuOH, t-BuOK
A)
B)
C)
D)
E) None of the above Ans: D
142
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 26. What is the major product for the following reaction? EtONa, EtOH I
heat
A)
B)
C)
D)
E) None of the above Ans: A
143
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 27. What is the major product for the following reaction? Cl EtOH, EtONa heat
A)
B)
C)
D)
E)
Ans: A
144
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Easy 28. What is the major product for the following reaction? Br
t-BuOK, t-BuOH
A)
B)
C)
D)
E)
Ans: E
145
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Medium 29. What is the major product for the following reaction? EtONa, EtOH Br
heat
A)
B)
C)
D)
E) More than one of the above Ans: C
146
Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms Section: 7.6 Difficulty 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 Synthesis Section: 7.6 Difficulty Level: Hard 31. What is the major product for the following reaction? EtOH, EtONa Br
heat
A) OEt
B) C) D) E) Ans: C
147
Topic: Alkene Synthesis Section: 7.6 Difficulty Level: Hard 32. What is the major product for the following reaction? EtOH, EtONa Cl
heat
A) OEt
B) C) D) E) Ans: B
148
Topic: Alkene Synthesis Section: 6.5, 7.6 Difficulty Level: Medium 33. What is the major product for the following reaction? 1. NaI, acetone OTs
2. t-BuOH, t-BuOK
A) B) C) D) E) Ans: C
149
Topic: Alkene Synthesis Section: 6.5, 7.6 Difficulty Level: Hard 34. What is the major product for the following reaction? 1. NaI, acetone Cl
2. t-BuOH, t-BuOK
A) B) C) D) E) Ans: D
150
Topic: Alkene Synthesis Section: 6.5, 7.6 Difficulty Level: Hard 35. What is the major product for the following reaction? 1. NaI, acetone Cl
2. NaOH, EtOH, heat
A) B) C) D) E) Ans: C
151
Topic: Alkene Synthesis Section: 6.5, 7.6 Difficulty Level: Hard 36. What is the major product for the following reaction? 1. NaI, acetone Br
2. EtONa, EtOH, heat
A) B) C) D) E) Ans: B
152
Topic: Alkene Synthesis, Reaction Mechanisms Section: 6.5, 6.16, 7.6 Difficulty Level: Medium 37. Which compound listed below would you expect to be the major product when 2-bromo2-methylbutane is refluxed with KOH/ethanol? A) OH B) O
C) D) E) Ans: D Topic: Alkene Synthesis Section: 7.6B Difficulty 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 β-hydrogen and leaving group can assume an antiperiplanar 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
153
Topic: Alkene Synthesis Section: 7.6C Difficulty 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 Mechanisms Section: 7.6C Difficulty Level: Easy 40. What is the major product of the reaction, (CH3)3COK ? (CH3)3COH heat Br A) B) C) D) E)
(CH3)2C=C(CH3)2 (CH3)3C–CH=CH2 (CH3)2C=CHCH3 (CH3)2C=CHCH2CH3 None of these Ans: B
154
Topic: Alkene Synthesis, Reaction Mechanisms Section: 7.6C Difficulty Level: Easy 41. Which compound would be the major product? Br (CH3)3COK ? (CH3)3COH heat O
A)
B) C) OH
D) E) Ans: E
155
Topic: Carbocation Stability, Rearrangement Section: 7.7 Difficulty Level: Easy 42. A) B) C) D) E)
Which statement(s) is/are true of acid-catalyzed alcohol dehydrations? Protonation of the alcohol is a fast step. Formation of a carbocation from the protonated alcohol is a slow step. Rearrangements of less stable carbocations to more stable carbocations are common. Loss of a proton by the carbocation is a fast step. All of the above Ans: E
Topic: Alkene Synthesis, Reaction Mechanisms Section: 7.7 Difficulty Level: Easy 43. Which product(s) would be produced by acid-catalyzed dehydration of 2-methyl-2pentanol? A) B)
and
C)
and
D) E) O
Ans: B
156
Topic: Alkene Synthesis; Alcohol Dehydration Section: 7.7 Difficulty Level: Easy 44. Which one of the following alcohols would dehydrate most rapidly when treated with sulfuric acid? OH
OH
I
OH
II
III OH
OH
IV A) B) C) D) E)
V
I II III IV V Ans: B
157
Topic: Alkene Synthesis; Alcohol Dehydration Section: 7.7 Difficulty Level: Easy 45. Which mechanistic step in the acid-catalyzed dehydration of 3,3-dimethyl-2-butanol is the rate determining step? A) Step 1: +
H3O+
OH
+
H2O
OH2
B) Step 2: +
H2O
OH2
C) Step 3:
D) Step 4a: +
H2O
+
H3O+
+
H 2O
+
H3O+
E) Step 4b:
Ans: B
158
Topic: Alkene Synthesis; Alcohol Dehydration Section: 7.7 Difficulty Level: Easy 46. Which alcohol would be most easily dehydrated? CH3 A) CH3CH2CCH2CH3 OH CH3
B)
CH3CH2CHCHCH3 OH CH3
C)
CH3CH2CHCH2CH2OH CH3 D) HOCH2CHCH2CH2CH3 CH2OH E) CH3CH2CHCH2CH3 Ans: A Topic: Alkene Synthesis; Alcohol Dehydration Section: 7.7 Difficulty Level: Easy 47. Which alcohol would be most easily dehydrated?
OH
OH
I
OH
II
III OH
OH
IV A) B) C) D) E)
V
I II III IV V Ans: B
159
Topic: Carbocation Stability Section: 7.7 Difficulty Level: Medium 48. Which alcohol would initially produce the most stable carbocation when treated with concentrated H2SO4? A) OH B)
OH
C) OH
D) HO
E) HO
Ans: A Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.7 Difficulty 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
160
Topic: Carbocation Stability, Rearrangement Section: 6.11B, 7.7B Difficulty Level: Easy 50. Which of the following carbocations would NOT be likely to undergo rearrangement? A) CH3CHCHCH3 CH3 CH3 B) CH3CHCCH3 CH3
C) D)
CH3 CH3CCH2CH3 CH3
CH3CHCH2 CH3 E) CH3CCHCH2CH3 CH3 Ans: C Topic: Carbocation Stability, Rearrangement Section: 7.8 Difficulty Level: Hard 51. Neopentyl alcohol, (CH3)3CCH2OH, cannot be dehydrated to an alkene without rearrangement. What is the chief product of dehydration?
I
II
IV A) B) C) D) E)
III
V
I II III IV V Ans: B
161
Topic: Carbocation Stability, Rearrangement Section: 5.12, 6.10, 6.17, 7.8 Difficulty Level: Medium 52. What is the major product of the reaction between methanol and (2R,3S)-2-bromo-3methylpentane at room temperature? A) B)
OCH3
C) D) H3CO
E) Both A) and C) Ans: D Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Easy 53. A) B) C) D) E)
Rearrangements are likely to occur in which of the following reaction types? SN1 reactions SN2 reactions E1 reactions E2 reactions Both SN1 and E1 reactions Ans: E
162
Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Easy 54. What is the major product of the reaction of the following reaction? I
A)
B)
ethanol, 20 oC
CH3CH2O
OCH2CH3
C)
D)
E) More than one of the above Ans: A
163
Topic: Alkene Synthesis Section: 6.10, 6.17, 7.8 Difficulty Level: Easy 55. What is the major product for the following reaction? Br
EtOH, heat
A)
B)
C)
D)
E) More than one of the above Ans: E
164
Topic: Alkene Synthesis Section: 6.10, 6.17, 7.8 Difficulty Level: Medium 56. What is the major product for the following reaction? I
EtOH, heat
A)
B)
C)
D)
E) None of the above Ans: C
165
Topic: Alkene Synthesis Section: 6.10, 6.17, 7.8 Difficulty Level: Medium 57. What is the major product for the following reaction? Cl
EtOH, heat
A)
B)
C)
D)
E)
Ans: D
166
Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Hard 58. What is the major product of the reaction of the following reaction? Cl
EtOH, heat
A) B) OEt
C) D)
E)
Ans: D
167
Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Hard 59. What is the major product of the reaction of the following reaction? EtOH, heat OTs
A)
B)
C)
OEt
D)
E) None of the above Ans: A
168
Topic: Carbocation Stability, Rearrangement Section: 6.10, 6.17, 7.8 Difficulty Level: Hard 60. What is the major product of the reaction of the following reaction? CH3OH, heat Cl
A) H3CO
B)
C)
D)
E) Ans: E
169
Topic: Carbocation Stability, Rearrangement Section: 4.16, 6.10, 6.17, 7.3, 7.8 Difficulty 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
170
Topic: Alkene Synthesis, Reaction Mechanisms, Carbocation Rearrangements Section: 7.7, 7.8 Difficulty Level: Medium 62. Which alkene would you expect to be the major product of the following dehydration? H2SO4 ?
heat OH
I
IV
A) B) C) D) E)
III
II
V
I II III IV V Ans: C
171
Topic: Alkene Synthesis, Reaction Mechanisms, Carbocation Rearrangements Section: 7.7, 7.8 Difficulty Level: Hard 63. What will be the major product of the following reaction? 85% H3PO4 ? heat OH
A)
B)
C) D)
O
E) Ans: A
172
Topic: Alkene Synthesis, Nomenclature Section: 7.6C, 7.7, 7.10 Difficulty 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) H2SO4 heat
OH
B)
(CH3)3COK, (CH3)3COH heat
Br
C) Br Br
i) 3 NaNH2, mineral oil, heat ii) H3O+
D) All of these E) Answers B) and C) only Ans: B Topic: Alkyne Synthesis Section: 7.11 Difficulty Level: Easy 65. A) B) C) D) E)
Which reaction would yield 2-butyne? − + CH3C≡ C: Na + CH3Br → − + CH3CH2Br + HC≡ C: Na → − + CH3: Na + HC≡ CCH3 → More than one of these None of these Ans: A
173
Topic: Alkyne Synthesis Section: 3.6, 7.11, 7.12 Difficulty Level: Hard 66. Which reaction conditions would not yield 2-butyne from 1-propyne? A) a. EtONa, EtOH b. CH3I B) a. CH3Li, THF b. CH3I C) a. NaNH2, NH3 (liq) b. CH3I
D) a. NaCH2CH3, THF b. CH3I E) More than one of these Ans: A
Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms Section: 7.6, 7.7, 7.11, 7.12 Difficulty Level: Easy 67. Which of the following reactions would yield 2-pentyne? I A) NaNH2 (1 mol) NaNH2
B)
Br
(1 mol)
C)
Br
CH3OH Br
D) E)
Br
HA heat
OH
NaOC2H5 C2H5OH Ans: B
174
Topic: Alkyne Synthesis Section: 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? CH3 A) C2H5 C C C: Na CH3
H3C
I
CH3
B) H3C C C:
Na
C)
C2H5 C Br CH3
NaNH2 ( excess) Br
Br
NH3 (l)
D) More than one of these E) None of these Ans: D Topic: Alkyne Synthesis Section: 7.11, 7.12 Difficulty Level: Easy 69. A) B) C)
Which statement is/are true about acetylide anions? They do not alkylate with secondary alkyl halides. Primary alkyl halides are best suited for alkylation. 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
175
Topic: Alkyne Synthesis Section: 7.11, 7.12 Difficulty Level: Medium 70. Which reaction would not result in alkylation of the acetylide anion? Br A) Li Cl B) Li C)
D)
Li
Br OTs
Li E) None of the above Ans: C
Topic: Alkyne Synthesis Section: 7.11, 7.12 Difficulty Level: Medium 71. Which reaction would not primarily proceed via an SN2 mechanism? Br A) Li Cl B) Li C)
D)
Li
Br OTs
Li E) All of them proceed via SN2 Ans: C
176
Topic: Alkene/Alkyne Reactions, Reaction Mechanisms Section: 3.16, 7.13 Difficulty 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) CH2CH3
B) CH=CHT
C) CH=CH2
D) CH2CH2T
E) None of the above Ans: D Topic: Structure Elucidation Section: 2.16, 4.16, 7.13 Difficulty 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-hexyne B) 5-methyl-2-hexyne C) 5-methyl-1,3-hexadiene D) 5-methyl-1-hexyne E) 2-methyl-1,5-hexadiene Ans: D
Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation 177
Section: 2.16, 4.16, 4.17, 7.13 Difficulty 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, 7.13 Difficulty 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:
I
II
IV A) B) C) D) E)
III
V
I II III IV V Ans: C
Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation 178
Section: 2.16, 4.16, 4.17, 7.13 Difficulty 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 2methylpentane? A) B) C) D) E) Ans: D Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation Section: 4.16, 4.17, 7.13 Difficulty Level: Easy 77. Upon catalytic hydrogenation, a compound C6H6 absorbs four moles of hydrogen. Select a structure for C6H6.
I A) B) C) D) E)
II
III
IV
I, II III II, III IV, V I, IV, V Ans: D
179
V
Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation Section: 4.16, 4.17, 7.13 Difficulty Level: Easy 78.
A) B) C) D) E)
X (C8H14)
H2, Pt
25oC Given: One can conclude that X has: no rings and no double bonds. no rings and one double bond. one ring and one double bond. two rings and no double bonds. one triple bond. Ans: C
Y (C8H16)
Topic: Index of Hydrogen Deficiency, Catalytic Hydrogenation Section: 4.16, 4.17, 7.13 Difficulty Level: Easy 79. On hydrogenation, a compound C9H12 absorbs 2 mol of hydrogen. Which of the following is a possible structure for the compound?
I
A) B) C) D) E)
I II III IV V Ans: D
III
II
IV
V
Topic: Alkene Synthesis 180
Section: 7.10A, 7.13 Difficulty Level: Medium 80. What is the major product for the following reaction sequence? 1a. NaNH2 (excess) mineral oil, heat Cl 1b. NH4Cl Cl
2. H2 (excess), Pd/C
A)
B)
C
C) D) E) None of the above Ans: E Topic: Alkene/Alkyne Reactions, Reaction Mechanisms Section: 3.16, 7.10A, 7.13 Difficulty Level: Medium 81. Which would be the major product of the following reaction sequence? 1a. NaNH2 (excess) Cl mineral oil, heat Cl 1b. T3O+ H
2. H2, Pd/C
A) B) C) D) E)
(CH3CH2)2C=C=CHT (CH3CH2)2C=C=CH2 (CH3CH2)2CHCCT (CH3CH2)2CHCH=CHT None of the above Ans: E
Topic: Alkene Synthesis
181
Section: 7.11, 7.12, 7.13 Difficulty Level: Medium 82. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) H 1b. CH3CH2CH2Br H
A) B) C) D)
2. H2 (excess), Pd/C
N H
E) None of the above Ans: B Topic: Alkene Synthesis Section: 7.11, 7.12, 7.13 Difficulty Level: Medium 83. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) 1b. CH3CH2CH2Br 2. H2 (excess), Pd/C A) B) CH3CH2CH2Br C) D) E) None of the above Ans: A
182
Topic: Alkene Reactions, Reaction Mechanisms Section: 4.16, 7.14A Difficulty Level: Medium 84. Which would be the major product of the following reaction?
D2, Ni
?
D
D
D CH3
CH3 H CH3
H
DD
D
I
H
II
III
CH3 DH D
D CH3
D H
IV A) B) C) D) E)
V
I II III IV V Ans: A
Topic: Alkene/Alkyne Reactions, Reaction Mechanisms
183
Section: 7.6, 7.14A Difficulty Level: Medium 85. Which would be the major product of the following reaction sequence? 1. EtOH, EtONa 2. D2, Pd/C
Br
A)
B)
C) D D H
D) D H D
E)
D D
Ans: C
Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms 184
Section: 7.6, 7.7, 7.15 Difficulty Level: Medium 86. A) B) C) D) E)
Which is not a satisfactory procedure for the synthesis of 3-methyl-1-butene? (CH3)2CHCΗΟΗCH3 + conc. H2SO4 (CH3)2CHC≡ CH + Li/liq.NH3 (CH3)2CHCH2CH2Br + CH3ONa/CH3OH (CH3)2CHCHBrCH3 + (CH3)3COK/(CH3)3COH (CH3)2CHC≡ CH + H2/Ni2B (P-2) Ans: A
Topic: Alkene Synthesis Section: 7.10, 7.15 Difficulty Level: Medium 87. What is the major product for the following reaction sequence? 1. NaNH2 (excess) Br mineral oil, heat Br
2. H2, Pd/CaCO3 quinoline
A) B) C) D) E) Ans: D
185
Topic: Alkene Synthesis Section: 7.10A, 7.15 Difficulty Level: Medium 88. What is the major product for the following reaction sequence? 1a. NaNH2 (excess) mineral oil, heat Cl 1b. NH4Cl Cl
2. H2, P-2
A)
B)
C
C) D) E) None of the above Ans: C Topic: Alkene Synthesis Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 89. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) H 1b. CH3CH2CH2Br H
A) B) C) D)
2a. Li, CH3CH2NH2 2b. NH4Cl
N H
E) None of the above Ans: C Topic: Alkene Synthesis 186
Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 90. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) H 1b. CH3CH2CH2Br H
A) B) C) D)
2. H2, Pd/CaCO3 quinoline
N H
E) None of the above Ans: C Topic: Alkene Synthesis Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 91. What is the major product for the following reaction sequence? 1a. NaNH2, NH3 (liq.) 1b. CH3CH2CH2Br 2a. Li, CH3CH2NH2 2b. NH4Cl A) B) CH3CH2CH2Br C) D) E) None of the above Ans: C
Topic: Alkene Synthesis 187
Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 92. What is the major product for the following reaction sequence? 1a. n-BuLi, THF 1b. CH3CH2CH2Br 2. H2, P-2 A) B) CH3CH2CH2Br C) D) E) None of the above Ans: D Topic: Alkene Synthesis, Nomenclature, Reaction Mechanisms Section: 7.6, 7.7, 7.13, 7.15 Difficulty Level: Easy 93. A) B) C) D) E)
Which of these is the most satisfactory method for the preparation of cis-2-pentene? CH3CHBrCH2CH2CH3 + (CH3)3COK/(CH3)3COH CH3C≡ CCH2CH3 + H2, Pt CH3C≡ CCH2CH3 + H2, Ni2B (P-2) CH3C≡ CCH2CH3 + Li/liq. NH3 CH3CH2CHBrCH2CH3 + CH3CH2ONa/CH3CH2OH Ans: C
Topic: Alkyne Synthesis, Nomenclature, Reaction Mechanisms
188
Section: 7.6, 7.13, 7.15 Difficulty Level: Easy 94. Which reaction would not be a method for preparing 5-methyl-1-hexyne? A) 1) NaNH2 (2 mol), liq NH3
Br
2) NH4+
B) HC
CNa
+ Cl
C) Li
D)
CH
1) NaNH2 (3 mol), liq NH3
Br Br
E)
+ HC
Br
Br
2) NH4+ 1) NaNH2 (3 mol), liq NH3
2) NH4+
Ans: C Topic: Alkyne Reduction, Nomenclature, Reaction Mechanisms Section: 7.13, 7.15 Difficulty Level: Easy 95. A) B) C) D) E)
Which of the following reductions of an alkyne is NOT correct? 2-Pentyne + 2H2/Pt pentane 2-Pentyne + H2/Ni2B Z-2-Pentene 2-Pentyne + Li/NH3(l) Z-2-Pentene All of the above are correct. None of the above is correct. Ans: C
Topic: Alkyne Synthesis, Catalytic hydrogenation 189
Section: 7.11, 7.15A Difficulty Level: Medium 96. The structure of the product, C, of the following sequence of reactions would be: NaNH2 NH3(l)
A
CH3CH2Br
A) B) C) Br
D)
E)
Ans: A
Topic: Alkene/Alkyne Reactions, Reaction Mechanisms
190
B
H2 Ni2B [P-2]
C
Section: 7.13, 7.15A Difficulty Level: Medium 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 D
D) E) None of the above Ans: B
Topic: Alkene/Alkyne Reactions, Reaction Mechanisms
191
Section: 6.5, 6.16, 7.11, 7.15A 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 D
B)
D
D
H D D
D
D
C)
H
H
D
D
D) E) None of the above Ans: A
Topic: Dissolving Metal Reduction; trans-hydrogenation 192
Section: 7.15B Difficulty Level: Easy 99. The structure of the product obtained from 2-butyne and Li/C2H5NH2 is: A) B) C)
HN
D) NH
E) Ans: A
193
SHORT ANSWER QUESTIONS Topic: General Information Section: 7.6B Difficulty 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 Information Section: 7.6C Difficulty 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 Information Section: 7.7 Difficulty Level: Easy 102. In a dehydration reaction, the leaving group is _______________. Ans: a molecule of water Topic: General Information Section: 7.7 Difficulty Level: Easy 103. Dehydration of alcohols requires a __________________ catalyst. Ans: strong acid Topic: General Information Section: 7.8 Difficulty 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
194
Topic: General Information Section: 7.10 Difficulty Level: Medium 105. Alkynes can be produced from either __________________ or _________________ dihalides. Ans: vicinal/geminal Topic: General Information Section: 7.14 Difficulty Level: Easy 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 Hydrogenation Section: 7.14 Difficulty Level: Easy 107. How will you prepare cis-1,2-dimethylcyclohexane from 1,2-dimethylcyclohexene? Ans: Catalytic hydrogenation with H2, Ni (or Pt/Pd) H2, Ni
Topic: General Information Section: 7.15 Difficulty Level: Easy 108. Syn hydrogenation of an alkyne will produce a _________ alkene. Ans: Cis / Z Topic: General Information Section: 7.15 Difficulty Level: Medium 109. Conversion of alkynes to E-alkenes (trans-alkenes) can be accomplished via a __________________ reaction. Ans: dissolving metal reduction
195
Topic: Alkyne Reduction Section: 7.15 Difficulty Level: Medium 110. How will you prepare trans-2-heptene from 2-heptyne? Ans: Dissolving metal reduction with metallic Na in NH3(l). Na, NH3 (l)
Topic: Nomenclature, Stereochemistry Section: 4.3, 4.5, 5.7, 7.2 Difficulty 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. 2-chloro-4-methyl-3-hexene Ans: Cl
H
H
(2R, 3E)
Cl
Cl
(2S, 3E)
H
H
(2R, 3Z)
Cl
(2S, 3Z)
Topic: Alkene Nomenclature, Relative Stability Section: 4.5, 7.3 Difficulty 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) dimethylcyclopentene
I
II
III
IV
V
VI
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 Mechanism 196
Section: 7.7 Difficulty Level: Medium 113. Provide a mechanistic explanation for the formation of the observed products in the following reaction. H3O+ OH heat Ans:
H
:
:O H
OH2
:O H
:
: :
OH
1)
H
OH2+
rearrangement [-H2O]
:
2)
H
H
:
3a)
:O H H
Both H
H
H
H
H
H
H
:
3b)
:O H
:O H H
:O H H
Topic: Nomenclature, Multistep Synthesis Section: 4.16, 7.7 Difficulty Level: Hard 114. Propose a two-step synthetic strategy for the synthesis of 2-methylhexane from 5-methyl2-hexanol. OH Ans: H3O+ H2 + Ni heat 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 2methylhexane Topic: Carbocation Stability, Rearrangement 197
Section: 7.8 Difficulty Level: Medium 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: 7.10 Difficulty Level: Medium 116. Complete the following reaction sequence, providing a brief rationale for your answer. O
i) PCl5
?
ii) 3 NaNH2, mineral oil, heat iii) H3O+ Ans:
O
Cl
: Na H3 O+ 3 NaNH2, mineral oil, heat (-2HCl) II III I 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.
PCl5
Cl
Topic: Nomenclature, Index of Hydrogen Deficiency, IR Spectroscopy, Catalytic Hydrogenation Section: 2.16, 7.13 198
Difficulty Level: Medium 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: H excess H2 Ni IR: 2140, 3310 cm-1
2,3-dimethylheptane
Substance Q: 5,6dimethyl-1-heptyne
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
199
Section: 7.11, 7.12, 7.15 Difficulty Level: Medium 118. Propose a reasonable synthetic strategy for the synthesis of trans-6-methyl-3-heptene from 4-methyl-1-pentyne. Ans: Na+: CH3CH2Br NaNH2 NH3 (l) Li, NH3(l)
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 Hydrogenation Section: 7.11, 7.12, 7.15A Difficulty Level: Medium 119. Complete the following reaction, giving structural details of all intermediates as well as the final product. ?
:
Ans:
1) NaNH2, NH3 (l) 2) CH3CH2CH2Br 3) H2, Lindlar catalyst NaNH2 NH3 (l)
Na
CH3CH2CH2Br H2 Lindlar catalyst
200
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