Keghan
Chapter 14
MULTIPLE CHOICE QUESTIONS
Topic: Bonding and Resonance
1. Which of the following is NOT true of benzene?
A) Benzene tends to undergo substitution rather than addition reactions, even though it has
a high index of hydrogen deficiency.
B) All of the hydrogen atoms of benzene are equivalent.
C) The carbon-carbon bonds of benzene are alternately short and long around the ring.
D) Only one o-dichlorobenzene has ever been found.
E) Benzene is more stable than the hypothetical compound 1,3,5-cyclohexatriene.
Ans: C
Topic: Bonding and Resonance
2.
A)
B)
C)
D)
E)
Which of the following is true of benzene?
Benzene tends to undergo addition rather than substitution reactions.
All of the hydrogen atoms of benzene are equivalent.
The carbon-carbon bonds of benzene are alternately short and long around the ring.
The benzene ring is a distorted hexagon.
Benzene has the stability expected for cyclohexatriene.
Ans: B
Topic: Bonding and Resonance
3.
A)
B)
C)
D)
E)
The carbon-carbon bonds in benzene are:
of equal length and are shorter than the double bond of ethene.
of equal length and are intermediate between a double bond and a single bond.
of unequal length and are alternately short and long around the ring.
due only to p-orbital overlap.
of equal length and intermediate between the carbon-carbon bond lengths in ethene and
ethyne.
Ans: B
Topic: Nomenclature, Bonding and Resonance
4. In which of the following compounds would the shortest carbon-carbon bond(s) be
found?
A) Toluene
B) 2-Ethylcyclopentene
C) 4-Methyl-1,3-cyclohexadiene
D) 3-Methyl-1-hexyne
E) 3-Methyl-1,3-hexadiene
Ans: D
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Keghan
Chapter 14
Topic: Bonding and Resonance
5. We now know that the two Kekule structures for benzene are related in the following
way:
A) They are each equally correct as a structure for benzene.
B) Benzene is sometimes one structure and sometimes the other.
C) The two structures are in a state of rapid equilibrium.
D) Neither of the two structures adequately describes benzene; benzene is a resonance
hybrid of the two.
E) None of the above
Ans: D
Topic: Nomenclature, Bonding and Resonance
6. In which of the following compounds would the longest carbon-carbon bond(s) be
found?
A) 2-bromobenzaldehyde
B) Vinylbenzene
C) 1,3,5-heptatriene
D) 2,4,6-octatriene
E) 2-Ethylbenzoic acid
Ans: D
Topic: Aromatic/ Antiaromatic/ Nonaromatic
7.
A)
B)
C)
D)
E)
Which of the following statements regarding the cyclopentadienyl radical is correct?
It is aromatic.
It is not aromatic.
It obeys Huckel's rule.
It undergoes reactions characteristic of benzene.
It has a closed shell of 6 pi-electrons.
Ans: B
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Chapter 14
Topic: Aromaticity, Huckel Rule
8. Which of the following would you expect to be aromatic?
H
H
A)
B)
C)
D)
E)
I
I
II
III
IV
V
Ans: E
II
III
IV
V
Topic: Aromaticity, Huckel Rule
9. Which of these would you expect to have significant resonance stabilization energy?
N
H
A)
B)
C)
D)
E)
N
I
II
I
II
III
All of the above
None of the above
Ans: D
III
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Chapter 14
Topic: Aromaticity, Huckel Rule
10. Of the following C-10 compounds, which is expected to possess the greatest resonance
(delocalization) energy?
I
A)
B)
C)
D)
E)
II
III
IV
I
II
III
IV
V
Ans: C
Topic: Aromaticity, Huckel Rule
11. Which of the following would you expect to be aromatic?
H H
A)
B)
C)
D)
E)
I
I
II
III
IV
None of these
Ans: B
II
III
IV
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V
Keghan
Chapter 14
Topic: Aromaticity, Huckel Rule
12. Which compound would you NOT expect to be aromatic?
N
A)
B)
C)
D)
E)
I
I
II
III
IV
V
Ans: E
S
N
O
B
H
II
III
R
IV
V
Topic: Aromaticity, Huckel Rule
13.
A)
B)
C)
D)
E)
Which annulene would you NOT expect to be aromatic?
[6]-Annulene
[14]-Annulene
[16]-Annulene
[18]-Annulene
[22]-Annulene
Ans: C
Topic: Aromaticity, Huckel Rule
14. Which of the following would you expect to be aromatic?
A)
B)
C)
D)
E)
I
II
I
II
III
IV
All of these
Ans: A
III
IV
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Chapter 14
Topic: Aromaticity, Huckel Rule
15. Which of these species is aromatic?
A)
B)
C)
D)
E)
O
O
N
H
O
N
H
O
S
I
I
II
III
IV
V
Ans: B
II
III
IV
V
Topic: Aromaticity, Huckel Rule
16. Which of the following structures would be aromatic?
K
-2
K
Br
Br
2K
A)
B)
C)
D)
E)
I
I
II
III
IV
V
Ans: B
II
III
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IV
V
Keghan
Chapter 14
Topic: Aromaticity, Huckel Rule
17. Which of the following would you expect to be antiaromatic?
A)
B)
C)
D)
E)
I
I
II
III
IV
V
Ans: C
II
III
IV
V
Topic: Aromaticity, Huckel Rule
18. Which of the following would you expect to be aromatic?
H H
I
A)
B)
C)
D)
E)
II
III
IV
I
II
III
IV
None of the above
Ans: C
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Chapter 14
Topic: Aromaticity, Huckel Rule
19. On the basis of molecular orbital theory and Huckel's rule, which molecules and/or ions
should be aromatic?
I
H
H H
II
III
H
IV
V
N
H
A)
B)
C)
D)
E)
H
VI
VII
I and V
III and VIII
IV, VII and IX
IV, VI, VII and IX
All of the structures, I-IX
Ans: D
H
H
VIII
IX
Topic: Aromaticity, Huckel Rule
20. On the basis of molecular orbital theory and Huckel's rule, which of these compounds
should be aromatic?
H H
A)
B)
C)
D)
E)
I
I
II
III
IV
V
Ans: E
II
III
IV
V
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Chapter 14
Topic: Aromaticity, Huckel Rule
21. Of Huckel's requirements for aromatic character, only this one is waived in the case of
certain compounds considered to be aromatic.
A) The ring system must be planar.
B) The system must be monocyclic.
C) There must be (4n + 2)  electrons.
D) The Huckel number of electrons must be completely delocalized.
E) None. All of these rules must apply in every case.
Ans: B
Topic: Aromaticity, Huckel Rule
22. Which of these is an aromatic molecule?
N
O
B
CH3
A)
B)
C)
D)
E)
I
I
II
III
IV
V
Ans: A
II
CH3
N
H
S
O
III
IV
V
Topic: Aromaticity, Huckel Rule
23. In which case is the indicated unshared pair of electrons NOT a contributor to the 
aromatic system?
N
H
A)
B)
C)
D)
E)
O
N
I
II
I
II
III
IV
None of these
Ans: B
H
III
IV
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Chapter 14
Topic: Chemical Tests and Reactions
24. Which reagent(s) would serve as the basis for a simple chemical test that would
distinguish between benzene and 1-hexene?
A) NaOH in H2O
B) Br2 in CCl4
C) AgNO3 in C2H5OH
D) NaHSO3 in H2O
E) None of these
Ans: B
Topic: Chemical Tests and Reactions
25. Which reagent(s) would serve as the basis for a simple chemical test that would
distinguish between ethylbenzene and vinylcyclohexane?
A) H2CrO4
B) LAH
C) NaBH4, H2O
D) KMnO4, OH, H2O
E) Two of the above
Ans: D
Topic: Chemical Tests and Reactions
26. Which reagent(s) would serve as the basis for a simple chemical test that would
distinguish between naphthalene and 2,4,6-decatriene?
A) NaOH in H2O
B) KMnO4, OH, H2O
C) NaBH4, H2O
D) H2CrO4
E) None of these
Ans: B
Topic: Chemical and Spectroscopic Analysis
27. Which reagent(s)/technique would serve to distinguish between azulene and
bicyclo[5.3.0]decane?
A)
B)
C)
D)
E)
Br2, CCl4
KMnO4, OH, H2O
NMR Spectroscopy
UV Spectroscopy
Two of these
Ans: E
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Chapter 14
Topic: Chemical Tests and Reactions
28. Which is the only one of these reagents which will react with benzene under the
specified conditions?
A) Cl2, FeCl3, heat
B) H2, 25°C
C) Br2/CCl4, 25°C, dark
D) KMnO4/H2O, 25°C
E) H3O+, heat
Ans: A
Topic: Nomenclature and Isomerism
29.
A)
B)
C)
D)
E)
Which dibromobenzene can, in theory, yield three mononitro derivatives?
o-Dibromobenzene
m-Dibromobenzene
p-Dibromobenzene
All of these
None of these
Ans: B
Topic: Nomenclature and Isomerism
30. If thiophene is an aromatic molecule and reacts similarly to benzene, how many
(neutral) monobromothiophenes could be obtained in the following reaction?
S
A)
B)
C)
D)
E)
Br2
FeBr3
1
2
3
4
5
Ans: B
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Chapter 14
Topic: Nomenclature and Isomerism
31. 2-Bromo-4-nitroaniline is:
Br
Br
NH2
Br
NO2
NO2
NH2
NO2
I
II
H2 N
III
OCH3
Br
Br
A)
B)
C)
D)
E)
H3CO
NO2
NO2
IV
V
I
II
III
IV
V
Ans: C
Topic: Nomenclature and Isomerism
32. 4-Bromo-2-nitroaniline is:
Br
Br
NH2
NO2
Br
NO2
NH2
NO2
I
II
H2 N
III
OCH3
Br
A)
B)
C)
D)
E)
Br
H3CO
NO2
NO2
IV
V
I
II
III
IV
V
Ans: A
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Chapter 14
Topic: Nomenclature and Isomerism
33. 4-Amino-2-chlorophenol is:
Cl
OH
Cl
O
O
Cl
NH2
NO2
I
II
H2 N
III
OH
OH
Cl
A)
B)
C)
D)
E)
Cl
NH2
NO2
IV
V
I
II
III
IV
V
Ans: D
Topic: Nomenclature and Isomerism
34. 4-Chloro-3-nitro-benzaldehyde is:
Cl
OH
Cl
O
O
Cl
NH2
NO2
I
II
H2 N
III
OH
Cl
A)
B)
C)
D)
E)
OH
Cl
NH2
NO2
IV
V
I
II
III
IV
V
Ans: B
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Chapter 14
Topic: Nomenclature and Isomerism
35. 4-amino-2-chlorobenzaldehyde is:
Cl
OH
Cl
O
O
Cl
NH2
NO2
I
II
H2 N
III
OH
OH
Cl
A)
B)
C)
D)
E)
Cl
NH2
NO2
IV
V
I
II
III
IV
V
Ans: C
Topic: Nomenclature and Isomerism
36. 4-amino-2-bromoanisole is:
Br
OCH3
Br
Br
O
H3CO
NH2
NO2
I
II
H2N
III
OCH3
Br
A)
B)
C)
D)
E)
OCH3
Br
NH2
NO2
IV
V
I
II
III
IV
V
Ans: D
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Chapter 14
Topic: Nomenclature and Isomerism
37. 4-bromomethyl-2-nitroanisole is:
Br
OCH3
Br
Br
O
H3CO
NH2
NO2
I
II
H2N
III
OCH3
Br
A)
B)
C)
D)
E)
OCH3
Br
NH2
NO2
IV
V
I
II
III
IV
V
Ans: B
Topic: Nomenclature and Isomerism
38.
A)
B)
C)
D)
E)
How many different dibromophenols are possible?
8
7
6
5
4
Ans: C
Topic: Nomenclature and Isomerism
39. The correct name for the compound shown below is:
Br
Br
NH2
A)
B)
C)
D)
E)
3,4-Dibromoaniline
2,4-Dibromoaniline
2,5-Dibromoaniline
3,6-Dibromoaniline
2,6-Dibromoaniline
Ans: C
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Chapter 14
Topic: Nomenclature and Isomerism
40.
A)
B)
C)
D)
E)
Which dibromobenzene can yield only one mononitro derivative?
o-Dibromobenzene
m-Dibromobenzene
p-Dibromobenzene
More than one of these
None of these
Ans: C
Topic: Nomenclature and Isomerism
41. A dichlorobenzene that on reaction with nitric acid and sulfuric acid might theoretically
yield three mononitro products would be:
A) o-Dichlorobenzene
B) m-Dichlorobenzene
C) p-Dichlorobenzene
D) None of these
E) All of these
Ans: B
Topic: Nomenclature and Isomerism
42.
A)
B)
C)
D)
E)
In theory, a single molecule of this compound will rotate plane-polarized light.
Butylbenzene
Isobutylbenzene
sec-Butylbenzene
tert-Butylbenzene
None of these
Ans: C
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Chapter 14
Topic: Nomenclature and Isomerism
43. Which of the following is NOT 2-bromo-5-nitrobenzoic acid?
Br
Br
HO
OH
O 2N
NO2
O
O
O
I
Br
II
Br
III
HO
HO
NO2
IV
A)
B)
C)
D)
E)
V
I
II
III
IV
V
Ans: D
Topic: Nomenclature and Isomerism
44.
A)
B)
C)
D)
E)
Toluene is the name commonly assigned to:
Hydroxybenzene
Aminobenzene
Methylbenzene
Ethylbenzene
Methoxybenzene
Ans: C
Topic: Nomenclature and Isomerism
45.
A)
B)
C)
D)
E)
O
Br
O
NO2
HO
Anisole is the name commonly assigned to:
Hydroxybenzene
Aminobenzene
Methylbenzene
Ethylbenzene
Methoxybenzene
Ans: E
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Keghan
Chapter 14
Topic: Nomenclature and Isomerism
46.
A)
B)
C)
D)
E)
Phenol is the name commonly assigned to:
Hydroxybenzene
Aminobenzene
Methylbenzene
Ethylbenzene
Methoxybenzene
Ans: A
Topic: Nomenclature and Isomerism
47.
A)
B)
C)
D)
E)
Aniline is the name commonly assigned to:
Hydroxybenzene
Aminobenzene
Methylbenzene
Ethylbenzene
Methoxybenzene
Ans: B
Topic: Nomenclature and Isomerism
48. The complete name for the following compound is:
CH3
H
A)
B)
C)
D)
E)
sec-Hexylbenzene
2-Phenylhexane
(R)-2-Phenylhexane
(S)-2-Phenylhexane
Butylmethylphenylmethane
Ans: D
Topic: Nomenclature and Isomerism
49.
A)
B)
C)
D)
E)
How many dichloronaphthalenes are possible?
7
8
9
10
12
Ans: D
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Keghan
Chapter 14
Topic: Nomenclature and Isomerism
50. Which of these is the single best representation for naphthalene?
II
I
IV
A)
B)
C)
D)
E)
III
V
I
II
III
IV
V
Ans: A
Topic: Molecular Orbital Theory
51. How many equivalent resonance structures can be written for the cyclopentadienyl
anion?
A) 3
B) 4
C) 5
D) 6
E) 7
Ans: C
Topic: Molecular Orbital Theory
52. In the molecular orbital model of benzene, the six p-orbitals combine to form how many
molecular orbitals?
A) 6
B) 5
C) 4
D) 3
E) 2
Ans: A
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Chapter 14
Topic: Molecular Orbital Theory
53. Consider the molecular orbital model of benzene. In the ground state how many
molecular orbitals are filled with electrons?
A) 1
B) 2
C) 3
D) 4
E) 5
Ans: C
Topic: Molecular Orbital Theory
54. In the molecular orbital model of benzene, how many pi-electrons are delocalized about
the ring?
A) 2
B) 3
C) 4
D) 5
E) 6
Ans: E
Topic: Molecular Orbital Theory
55. In the molecular orbital model of benzene, how many pi-electrons are in bonding
molecular orbitals?
A) 6
B) 5
C) 4
D) 3
E) 2
Ans: A
Topic: Molecular Orbital Theory
56. Consider the molecular orbital model of cyclopentadienyl anion. In the ground state
how many molecular orbitals are filled with electrons?
A) 1
B) 2
C) 3
D) 4
E) 5
Ans: C
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Keghan
Chapter 14
Topic: Molecular Orbital Theory
57. In the molecular orbital model of cyclopentadienyl anion, how many pi-electrons are
delocalized about the ring?
A) 2
B) 3
C) 4
D) 5
E) 6
Ans: E
Topic: Molecular Orbital Theory
58. In the molecular orbital model of cyclopentadienyl anion, how many pi-electrons are in
bonding molecular orbitals?
A) 6
B) 5
C) 4
D) 3
E) 2
Ans: A
Topic: Molecular Orbital Theory
59. In the molecular orbital model of cycloheptadienyl cation, how many pi-electrons are in
bonding molecular orbitals?
A) 6
B) 5
C) 4
D) 3
E) 2
Ans: A
Topic: Molecular Orbital Theory
60. In the molecular orbital model of cycloheptadienyl cation, how many pi-electrons are
delocalized about the ring?
A) 6
B) 5
C) 4
D) 3
E) 2
Ans: A
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Chapter 14
Topic: Molecular Orbital Theory
61. In the molecular orbital model of 1,3-cyclobutadiene, how many electrons are in nonbonding molecular orbitals?
A) 6
B) 5
C) 4
D) 3
E) 2
Ans: E
Topic: Molecular Orbital Theory
62. In the molecular orbital model of which of the following substance(s) are non-bonding
orbitals found?
A) 1,3-Cyclobutadiene
B) Cyclopentadienyl anion
C) 1,3,5,7-Cyclooctatetraene
D) Two of the above
E) All of the above
Ans: D
Topic: Molecular Orbital Theory
63. Which cyclization(s) should occur with a decrease in pi-electron energy?
A)
B)
C)
D)
E)
I
CH2
CH
CH
II
CH2
CH
CH2
III CH2
CH
CH2
IV CH2
CH
CH2
CH2
+ H2
+ H2
+ H2
+ H2
I
II
III
IV
All of the above
Ans: B
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Chapter 14
Topic: Molecular Orbital Theory
64. Application of the polygon-and-circle technique reveals that single electrons occupy
each of the two nonbonding orbitals in the molecular orbital diagram of:
A) Cyclobutadiene
B) Benzene
C) Cyclopropenyl cation
D) Cyclopentadienyl anion
E) Cycloheptatrienyl cation
Ans: A
Topic: Explanations and Predictions
65.
A)
B)
C)
D)
E)
Why would 1,3-cyclohexadiene undergo dehydrogenation readily?
It is easily reduced.
Hydrogen is a small molecule.
1,3-Cyclohexadiene has no resonance energy.
It would gain considerable stability by becoming benzene.
It would not undergo dehydrogenation.
Ans: D
Topic: Explanations and Predictions
66.
A)
B)
C)
D)
E)
Which of the following statements about cyclooctatetraene is NOT true?
The compound rapidly decolorizes Br2/CCl4 solutions.
The compound rapidly decolorizes aqueous solutions of KMnO4.
The compound readily adds hydrogen.
The compound is nonplanar.
The compound is comparable to benzene in stability.
Ans: E
Topic: Explanations and Predictions
67. Cyclopentadiene is unusually acidic for a hydrocarbon. An explanation for this is the
following statement.
A) The carbon atoms of cyclopentadiene are all sp2-hybridized.
B) Cyclopentadiene is aromatic.
C) Removal of a proton from cyclopentadiene yields an aromatic anion.
D) Removal of a hydrogen atom from cyclopentadiene yields a highly stable free radical.
E) Removal of a hydride ion from cyclopentadiene produces an aromatic cation.
Ans: C
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Chapter 14
Topic: Explanations and Predictions
68. Recalling that benzene has a resonance energy of 152 kJ mol-1 and naphthalene has a
resonance energy of 255 kJ mol-1, predict the positions which would be occupied by
bromine when phenanthrene (below) undergoes addition of Br2.
3
4
5
6
2
7
1
8
10
A)
B)
C)
D)
E)
9
1, 2
1, 4
3, 4
7, 8
9, 10
Ans: E
Topic: Spectroscopy
69. Which isomer of C7H7Cl exhibits strong IR absorbances at 690 and 750 cm1?
CH3
CH3
CH3
CH2Cl
Cl
Cl
Cl
I
A)
B)
C)
D)
E)
II
III
IV
I
II
III
IV
II and IV
Ans: E
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Chapter 14
Topic: Spectroscopy
70. Which of these compounds absorbs at the longest wavelength in the UV-visible region?
I
A)
B)
C)
D)
E)
II
III
IV
V
I
II
III
IV
V
Ans: B
Topic: Spectroscopy
71. A compound has the formula C8H9Br. Its 1H NMR spectrum consists of:
doublet,  2.0
quartet,  5.15
multiplet,  7.35
The IR spectrum shows two peaks in the 680-840 cm-1 region; one is between 690 and
710 cm-1 and the other is between 730 and 770 cm-1. Which is a possible structure for
the compound?
Br
Br
Br
II
I
III
Br
Br
IV
A)
B)
C)
D)
E)
V
I
II
III
IV
V
Ans: D
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Keghan
Chapter 14
Topic: Spectroscopy
72. Which of the following substances, formula C8H9Br, might exhibit the following 1H
NMR spectrum ?
triplet,  2.8
triplet,  4.65
multiplet,  7.2
Br
Br
Br
II
I
III
Br
Br
IV
A)
B)
C)
D)
E)
V
I
II
III
IV
V
Ans: C
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Keghan
Chapter 14
Topic: Spectroscopy
73. Which of the following substances, formula C8H9Br, might exhibit the following 1H
NMR spectrum ?
triplet,  1.2
quartet,  2.45
multiplet,  7.4
Br
Br
Br
II
I
III
Br
Br
IV
A)
B)
C)
D)
E)
V
I
II
III
IV
V
Ans: A
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Keghan
Chapter 14
Topic: Spectroscopy
74. Which of the following substances, formula C8H9Br, might exhibit the following 1H
NMR spectrum ?
singlet,  2.45
singlet,  2.5
multiplet,  7.35
Br
Br
Br
II
I
III
Br
Br
V
IV
A)
B)
C)
D)
E)
I
II
III
IV
V
Ans: E
Topic: Spectroscopy
75. Which of the following substances, C8H9Cl, would exhibit five signals in its 13C NMR
spectrum?
Cl
Cl
Cl
I
III
II
Cl
Cl
IV
A)
B)
C)
D)
E)
V
I
II
III
IV
V
Ans: C
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Keghan
Chapter 14
Topic: Spectroscopy
76. Which of the following substances, C9H10O, would exhibit seven signals in its 13C NMR
spectrum?
O
O
O
I
II
III
HO
O
V
IV
A)
B)
C)
D)
E)
I
II
III
IV
V
Ans: A
Topic: Spectroscopy
77. For which of the following substances, C9H10O, would the aromatic multiplet, in its 1H
NMR spectrum, consist of two doublets?
O
O
O
I
II
III
HO
O
IV
A)
B)
C)
D)
E)
V
I
II
III
IV
V
Ans: A
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Keghan
Chapter 14
Topic: Spectroscopy
78. In the 1H NMR spectra of which of the following substances, C9H10O, would you expect
to see two singlets in the range of  2.0-2.5 ppm?
O
O
I
O
II
III
HO
O
IV
A)
B)
C)
D)
E)
V
I and III
I, II, and III
IV
V
All of the above substances would exhibit two singlets 2.0-2.5 ppm in their 1H NMR
spectra
Ans: B
SHORT ANSWER QUESTIONS
Topic: General Concepts
79. A compound that reacts like an alkane, alkene, alkyne, or one of their derivatives, is
called an _____________ compound, while one that reacts like benzene is called an
_____________ compound.
Ans: aliphatic, aromatic
Topic: Nomenclature
80. When a benzene ring is used as a substituent, it is called a _________ group.
Ans: phenyl
Topic: General Concepts
81. The difference between the amount of heat actually released upon hydrogenation of
benzene and that calculated on the basis of the Kekule structure is called the
____________________ of benzene.
Ans: resonance energy
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Keghan
Chapter 14
Topic: General Concepts
82. Molecular orbitals of equal energy are referred to as _________ orbitals.
Ans: degenerate
Topic: Huckel’s rule
83. Hückel's Rule requires _________  electrons for an aromatic compound.
Ans: 4n+2
Topic: General Concepts
84. Monocyclic compounds with alternating single and double bonds are called
__________.
Ans: annulenes
Topic: General Concepts
85. Cagelike molecules with the geometry of a truncated icosahedron are called
___________.
Ans: fullerenes
Topic: Aromaticity, Reactivity
86. Pyrrole is not particularly basic, because the lone pair on the nitrogen is
______________.
Ans: part of the aromatic system
Topic: General Concepts
87. Humans do not have the biochemical ability to synthesize the benzene ring. Therefore,
two amino acids, _____________ and ___________, are essential to the human diet.
Ans: tryptophan, phenylalanine
Topic: Aromaticity, Reactivity
88. Benzene, while unusually unreactive, will react under certain conditions. However,
when it does react, it does so by ___________ rather than by addition.
Ans: substitution
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Keghan
Chapter 14
Topic: Nomenclature
89. Draw the structure corresponding to the following name: 2-bromo-5-nitrophenol
OH
Ans:
Br
O 2N
Topic: Nomenclature
90. Draw the structure corresponding to the following name:
3-bromo 5-phenylacetophenone
NH2
Ans:
Br
Topic: Nomenclature
91. Draw the structure corresponding to the following name: 2-hydroxy-4-(3methylcyclopentyl)benzoic acid
HO
Ans:
HO2C
Topic: Nomenclature
92. Draw the structure corresponding to the following name: 3-nitro-4-iodoanisole
O
Ans: O2N
I
Topic: Nomenclature
93. Give the IUPAC name for the following substance:
OH
O
Ans: 2-methyl-4-(3-methylbutyl)benzoic acid
Topic: Resonance
94. Draw all significant resonance structures for pyridine, C6H5N
Ans:
..N
N
..
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Keghan
Chapter 14
Topic: Resonance
95. Draw all significant resonance structures for azulene, C10H8
Ans:
Topic: Aromaticity
96. Briefly explain why the aromatic hydrocarbon azulene, C10H8, possesses a significant
dipole moment. Use diagrams as needed to illustrate/clarify your answer.
Ans: Azulene has the bicyclic structure shown below. Since the “non-polar” resonance
hybrid meets the Huckel rule for aromaticity, it accounts for the observed
aromatic properties of azulene. However, closer scrutiny suggests that a shift in
electron density, in which the 7-membered ring is electron deficient and the 5membered ring is electron-rich would be especially stable: each ring is now
independently aromatic, an aromatic cycloheptatrienyl cation fused with an
aromatic cyclopentadienyl anion. Thus, the most stable pi-electron distribution
would suggest a polar structure for azulene, accounting for this substance having a
significant dipole moment.
non-polar
polar
Topic: Aromaticity, Molecular Orbital Theory
97. Use the “polygon-in-circle” method to draw an MO diagram showing the pi-electron
distribution pattern in the cyclopentadienyl anion. How is this diagram useful in
explaining the aromatic properties of this anion?
Ans: The following MO diagram can be generated using the polygon-in-circle method.
The six pi electrons of the cyclopentadienyl anion in the bonding molecular
orbitals form a closed bonding shell, accounting for its aromatic properties.
Antibonding MO
Bonding MO
6 pi electrons
"closed bonding shell"
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Keghan
Chapter 14
Topic: Aromaticity, Reactivity
H
..
98. Explain briefly why cyclopentadiene readily reacts with strong bases.
Ans: The acidity of a substance can be often be correlated with the stability of its
conjugate base: substances that have exceptionally stable conjugate bases tend to
be strong acids. The conjugate base of cyclopentadiene, formed during reaction
with a base, is exceptionally stable, by virtue of being an aromatic anion (6 pi
electrons, planar ring), thus accounting for the readiness with which
cyclopentadiene reacts with bases.

B:
H
H
Aromatic
anion
Topic: Resonance, Bond Lengths
99. Although all bond lengths in benzene are identical, that is not always true for all
aromatic compounds. In naphthalene, for instance, the C1-C2 bond is shorter than the
C2-C3 bond. Explain, using resonance theory.
Ans: The major resonance structures for naphthalene are drawn below. The observed
bond lengths reflect the contribution of each structure to the overall resonance
hybrid:
The C1-C2 bond: two double bonds (I and II), and one single bond (III)
The C2-C3 bond: one double bond (III), and two single bonds (I and II)
Overall: C1-C2 bond more double-bond-like, thus shorter.
shorter
I
1
1
1
1
2
2
2
2
3
3
3
3
II
III
522
IV
longer
Keghan
Chapter 14
Topic: Aromaticity, Resonance Stabilization Energy
100. The heats of hydrogenation for cyclohexene and benzene are given below. Calculate the
resonance stabilization energy of benzene.
C6H10 + H2  C6H12
Ho = -120 kJ/mol
C6H6 + 3H2  C6H12
Ho = -208 kJ/mol
Ans: The resonance stabilization energy of benzene is the difference between the
theoretical and observed Ho values.
Hydrogenation of three double bonds should release 3 times the energy released
when one double bond is hydrogenated. Thus, the theoretical Ho for benzene
can be calculated as [3x (-120)] kJ/mol = -360 kJ/mol
Therefore,
Resonance stabilization energy of benzene = (-208) – (-360) kJ/mol
= 152 kJ/mol
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Keghan
Chapter 14
Topic: Aromaticity, Reactivity
101. The Lewis structures of both pyridine and pyrrole have an electron pair on the nitrogen
atom, suggesting that both substances might possess basic properties. However, only
pyridine reacts readily with HCl to form pyridinium chloride, while pyrrole is rather
unreactive. Explain clearly, using relevant diagrams to illustrate/clarify your answer.
Ans:
+ HCl
N
..
N+ 
Cl
H
2
sp
pyridinium chloride
pyridinium chloride
p
..
N H
+ HCl
H

N + Cl
H
X
not aromatic
pyrrole
electron pair:
part of aromatic pi sextet
Both pyridine and pyrrole are known to exhibit aromatic properties; the nitrogen
atom must therefore be sp2 hybridized in both cases.
In the pyridine molecule, this places the electron pair in an sp2 hybrid orbital, and
not involved in the aromatic  sextet needed for aromatic stability; the electron
pair is thus “available” for reacting with HCl, forming pyridinium chloride, while
preserving aromatic stability.
By contrast, the electron pair in pyrrole must be placed in the p orbital, since all
three sp2 orbitals are used in sigma bonds with neighboring atoms. This allows
the electron pair to contribute to aromatic stability by becoming part of the
aromatic sextet. Thus, the electron pair on nitrogen is not “available” for reacting
with HCl, because doing so would destroy the aromaticity of the ring.
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Keghan
Chapter 14
Topic: Aromaticity, Bonding
102. Consider the oxygen atom in the molecules of furan and tetrahydrofuran. Bearing in
mind that furan exhibits aromatic properties, compare the hybridization of oxygen in
both species, explaining why it must be different, although at first glance, it may appear
identical.
..
..
O.
O.
.
.
Furan
Ans:
THF
p
..
O
..
.. sp2
O
2
..
sp3
sp3
3
Furan: sp hybridized
one electron pair in p orbital:
Tetrahydrofuran: sp hybridized
both electron pairs
part of aromatic pi sextet
in sp orbitals
3
Oxygen has 2 lone electron pairs in both species and, at first glance, it might
appear that the hybridization patterns are identical. In THF, the oxygen atom is
sp3 hybridized and both pairs can be placed in sp3 hybrid orbitals. In furan, there
are two possibilities that must be considered: i) the oxygen may be sp3 hybridized,
with both electron pairs sp3 hybrid orbitals, as in THF, or, ii) oxygen may be sp2
hybridized, with one electron pair in an sp3 hybrid orbital, the other in a p orbital.
In the latter case, the electrons in the p orbital can then become part of an
aromatic sextet, allowing the molecule to gain aromatic stability. Since furan is
known to exhibit markedly aromatic properties, the oxygen must be sp2
hybridized.
525