Download - Chapter 16 organic chemistry
-
1
Organic Chemistry, 7e (Wade)
Chapter 16 Aromatic Compounds
1) Which of the following is an incorrect description of benzene?
A) The CCC bond angles are all equal to 120.
B) The molecule is planar.
C) The molecule is a 6-membered ring which contains alternating single and double carbon-
carbon bonds.
D) The molecule is aromatic.
E) The molecule can be drawn as a resonance hybrid of two Kekule structures.
Answer: C
Diff: 1
Section: 16.2
2) What is the bond order of the carbon-carbon bonds in benzene?
A) 0.5
B) 1
C) 1.5
D) 2
E) 3
Answer: C
Diff: 2
Section: 16.2
3) Cyclic hydrocarbons which can be represented as structures containing alternating single and
double bonds are called __________.
Answer: annulenes
Diff: 1
Section: 16.2
4) When cyclohexene is treated with KMnO4, H2O, the syn-1,2-diol is produced. What reaction
occurs when benzene is similarly treated?
Answer: No reaction takes place.
Diff: 2
Section: 16.2
5) Why does benzene undergo a substitution reaction with Br2 while cyclohexene undergoes an
addition reaction.
Answer: Addition of Br2 to benzene is highly unfavorable because it would result in a
nonaromatic product (aromatic stabilization would be lost).
Diff: 2
Section: 16.2
-
2
6) What is suggested by the fact that benzene's molar heat of hydrogenation is 36 kcal less than
three times the molar heat of hydrogenation of cyclohexene?
Answer: This suggests that the type of bonding in benzene lends special stability to the molecule.
Diff: 2
Section: 16.2
7) In the molecular orbital representation of benzene, how many molecular orbitals are present?
A) 1
B) 2
C) 4
D) 6
E) 8
Answer: D
Diff: 1
Section: 16.3
8) How many distinct nodal planes which are perpendicular to the molecular plane are present in
the 4* orbital of benzene?
A) 0
B) 1
C) 2
D) 4
E) 5
Answer: C
Diff: 2
Section: 16.3
9) How many pairs of degenerate molecular orbitals are found in benzene? A) 6
B) 5
C) 4
D) 3
E) 2
Answer: E
Diff: 2
Section: 16.3
-
3
10) Which of the following undergoes SN2 reaction with sodium methoxide most rapidly?
A) PhCH2Br
B) Ph3CBr
C) PhCH2CH2Br
D) PhBr
E) PhCH2CH2CH2Br
Answer: A
Diff: 2
Section: 16.3
11) Which of the following undergoes solvolysis in methanol most rapidly?
A) PhCH2Br
B) Ph3CBr
C) PhCH2CH2Br
D) PhBr
E) PhCH2CH2CH2Br
Answer: B
Diff: 2
Section: 16.3
12) Provide a diagram which depicts the relative energies of the molecular orbitals of benzene. Show which molecular orbitals are filled in benzene's ground state.
Answer:
Diff: 3
Section: 16.3
13) Show how the participating p orbitals interact to form the highest energy molecular orbital of benzene.
Answer: All adjacent interactions are antibonding.
Diff: 2
Section: 16.3
-
4
14) Show how the p orbitals overlap to generate the p4* of cyclobutadiene.
Answer:
Diff: 2
Section: 16.4
15) Describe the occupied p molecular orbitals in the ground state of cyclobutadiene.
Answer: Two electrons are paired in a bonding p molecular orbital, while the other two
electrons are unpaired and singly occupy two nonbonding p molecular orbitals.
Diff: 3
Section: 16.4
16) What is the major difference between an antiaromatic and aromatic compound?
A) The structure must be cyclic for aromatic but not antiaromatic compounds?
B) Antiaromatic compounds have at least one sp3 hybridized atom in the ring
C) Antiaromatic compounds can assume a chair-like structure while aromatic compounds are
nearly flat
D) Aromatic compounds cannot have a charged atom in the structure
E) Only aromatic compounds follow Huckle's rule.
Answer: E
Diff: 1
Section: 16.5
17) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity
of the network.
Answer: nonaromatic
Diff: 2
Section: 16.5
-
5
18) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity
of the network.
Answer: nonaromatic
Diff: 2
Section: 16.5
19) Classify the following compound as aromatic, antiaromatic, or nonaromatic.
Answer: Aromatic
Diff: 3
Section: 16.5
20) Classify the following compound as aromatic, antiaromatic, or nonaromatic.
Answer: nonaromatic (not planar nor continuous)
Diff: 3
Section: 16.5
21) Classify the following compound as being aromatic, nonaromatic or antiaromatic.
Answer: antiaromatic (8 electrons)
Diff: 3
Section: 16.5
-
6
22) Aromatic molecules contain __________ electrons. A) no
B) 4n + 1 (with n an integer)
C) 4n + 2 (with n an integer)
D) 4n (with n an integer)
E) unpaired
Answer: C
Diff: 1
Section: 16.6
23) Which of the following is another name for cyclobutadiene?
A) [2]annulene
B) [4]annulene
C) [6]annulene
D) Dewar benzene
E) antibenzene
Answer: B
Diff: 1
Section: 16.6
-
7
24) Which of the following structures, if flat, would be classified as antiaromatic?
A)
B)
C)
D)
E)
Answer: C
Diff: 2
Section: 16.6
25) Classify 1,3,5-heptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the
network. Answer: nonaromatic
Diff: 1
Section: 16.6
-
8
26) List the criteria which compounds must meet in order to be considered aromatic.
Answer:
1. The structure must be cyclic.
2. Each atom in the ring must have an unhybridized p orbital.
3. The structure must be planar or nearly planar so that overlap of these p orbitals is effective.
4. The network must contain 4n + 2 electrons (where n is a whole number), so that delocalization of the electrons results in a lowering of the molecule's electronic energy. Diff: 2
Section: 16.6
27) Which is more stable, cyclobutadiene or 1,3-butadiene? Explain.
Answer: 1,3-Butadiene is more stable. Cyclobutadiene is antiaromatic since it contains 4 (i.e.,
4n) electrons. Antiaromatic systems are less stable than their open-chain counterparts. Diff: 2
Section: 16.6
28) Is cyclooctatetraene a planar molecule? Explain.
Answer: No. In addition to increasing other forms of strain, a planar conformation would make
this molecule antiaromatic.
Diff: 2
Section: 16.6
29) Classify cycloheptatriene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the
network. Answer: nonaromatic
Diff: 2
Section: 16.6
30) Classify cyclopentadiene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the
network. Answer: nonaromatic
Diff: 2
Section: 16.6
31) Is the all-cis form of [10]annulene aromatic? Explain.
Answer: No. Planarity, which is required for aromaticity, is precluded due to excessive angle
strain.
Diff: 3
Section: 16.6
32) Is the [10]annulene shown below aromatic? Explain.
Answer: No. The ring cannot achieve a planar conformation since such a conformation would
result in severe and unfavorable steric interactions between the two H's oriented inside the ring.
Diff: 3
Section: 16.6
-
9
33) Classify the compound below as aromatic antiaromatic, or nonaromatic. Assume planarity of
the network.
Answer: aromatic
Diff: 3
Section: 16.6
34) Which of the following is the same as the tropylium ion?
A) cycloheptatrienyl cation
B) cycloheptatrienyl anion
C) cyclopentadienyl cation
D) cyclopentadienyl anion
E) cyclopropenyl anion
Answer: A
Diff: 2
Section: 16.8
-
10
35) Which of the following structures is aromatic?
A)
B)
C)
D)
E)
Answer: A
Diff: 2
Section: 16.8
-
11
36) Which of the labeled H atoms (1 -5) in the following molecule would be predicted to be the
most acidic?
A) 1
B) 2
C) 3
D) 4
E) 5
Answer: A
Diff: 3
Section: 16.8
37) Rank the following in order of increasing pKa (from lowest to highest pKa)
A) 1 < 2 < 3
B) 3 < 2 < 1
C) 2 < 1 < 3
D) 3 < 1 < 2
E) 2 < 3 < 1
Answer: C
Diff: 3
Section: 16.8
-
12
38) Which sequence ranks the indicated protons in order of increasing acidity?
A) 1 < 2 < 3
B) 2 < 3 < 1
C) 3 < 1 < 2
D) 3 < 2 < 1
Answer: D
Diff: 3
Section: 16.8
39) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity
of the network.
Answer: aromatic
Diff: 1
Section: 16.8
40) Provide the structure of tropylium bromide.
Answer:
Diff: 2
Section: 16.8
-
13
41) Provide the structure of sodium cyclopentadienide.
Answer:
Diff: 2
Section: 16.8
42) What compound results when cyclooctatetraene is treated with excess potassium metal?
Answer: dipotassium cyclooctatetraene dianion
Diff: 3
Section: 16.8
43) Add six pi bonds to the structure below to produce the most stable isomer.
Answer:
Diff: 3
Section: 16.8
44) Provide the major resonance structures of the ion which results when the most acidic
hydrogen of cyclopentadiene is lost.
Answer:
Diff: 2
Section: 16.8
45) Explain the relative acidities of cyclohexene (pKa of 46) and cyclopentadiene (pKa of 16).
Answer: The conjugate base of cyclopentadiene is aromatic.
Diff: 2
Section: 16.8
-
14
46) Why would the reaction below proceed at an extremely slow rate if at all?
Answer: The carbocation intermediate involved in this reaction is antiaromatic. Based on
Hammond's Postulate, one can surmise that the activation energy required to produce this
intermediate would be very high.
Diff: 2
Section: 16.8
47) When cycloheptatriene is deprotonated, an anion with seven resonance forms of equal energy
can be drawn. Given this fact, explain why cycloheptatriene is only slightly more acidic than
propene.
Answer: Each resonance form of the cyclopehtatrienyl anion is antiaromatic.
Diff: 2
Section: 16.8
48) 3-Chlorocyclopropene is solvolyzed in methanol at a much higher rate than is
chlorocyclopropane. Offer an explanation.
Answer: Cyclopropenyl cation, the carbocationic intermediate in the case of 3-chlorocycloprene,
is aromatic and via Hammond's Postulate we can say that the activation energy required to form
it is lower.
Diff: 2
Section: 16.8
49) Classify cyclopentadienyl cation as aromatic, antiaromatic, or nonaromatic. Assume
planarity of the network. Answer: antiaromatic
Diff: 2
Section: 16.8
50) Classify cyclopropenyl cation as aromatic, antiaromatic, or nonaromatic. Assume planarity
of the network Answer: aromatic
Diff: 2
Section: 16.8
51) Classify cycloheptatrienyl cation as aromatic, antiaromatic, or nonaromatic. Assume
planarity of the network. Answer: aromatic
Diff: 2
Section: 16.8
-
15
52) Nitrogen's lone pair electrons occupy what type of orbital in pyridine?
A) s
B) sp
C) sp2
D) sp3
E) p
Answer: C
Diff: 2
Section: 16.9
53) Classify pyrrole as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.
Answer: aromatic
Diff: 2
Section: 16.9
54) __________ is similar to furan, with a sulfur atom in place of the oxygen.
Answer: Thiophene
Diff: 2
Section: 16.9
55) Is the molecule below aromatic, antiaromatic, or nonaromatic?
Answer: aromatic
Diff: 2
Section: 16.9
56) Is the molecule below aromatic, antiaromatic, or nonaromatic?
Answer: aromatic
Diff: 2
Section: 16.9
-
16
57) Is the molecule below aromatic, antiaromatic, or nonaromatic?
Answer: nonaromatic
Diff: 2
Section: 16.9
58) Is the molecule below aromatic, antiaromatic, or nonaromatic?
Answer: nonaromatic
Diff: 2
Section: 16.9
59) Is the molecule below aromatic, antiaromatic, or nonaromatic?
Answer: aromatic
Diff: 2
Section: 16.9
-
17
60) Circle and name the aromatic heterocycles in the following structure, which has been found
to be effective against inflammatory diseases including Alzheimer's disease and rheumatoid
arthritis (J. Med. Chem. 2007, 4728).
Answer:
Diff: 2
Section: 16.9
61) Classify pyridine as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.
Answer: aromatic
Diff: 2
Section: 16.9
62) Which is more basic, pyridine or pyrrole? Explain.
Answer: Pyrrole is a much weaker base than pyridine. When pyrrole is protonated, the system's
aromaticity is destroyed.
Diff: 2
Section: 16.9
63) Provide the structure of pyrimidine.
Answer:
Diff: 2
Section: 16.9
-
18
64) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity
of the network.
Answer: aromatic
Diff: 3
Section: 16.9
65) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity
of the network.
Answer: aromatic
Diff: 3
Section: 16.9
66) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity
of the network.
Answer: antiaromatic
Diff: 2
Section: 16.10
67) Classify naphthalene as aromatic, antiaromatic, or nonaromatic. Assume planarity of the network.
Answer: aromatic
Diff: 1
Section: 16.10
68) Why are researchers interested in the properties of large polynuclear aromatic hydrocrobons?
Answer: These compounds are formed to some extent in nearly all combustion reactions of
organic compounds and are known to be potent carcinogens.
Diff: 2
Section: 16.10
-
19
69) Provide the structure of the major organic product which results when phenanthrene is
treated with Br2 in carbon tetrachloride.
Answer:
Diff: 2
Section: 16.10
70) Provide the structure of anthracene.
Answer:
Diff: 2
Section: 16.10
71) Name two of the three common allotropes of carbon.
Answer: diamond; graphite; fullerenes (like buckminsterfullerene)
Diff: 1
Section: 16.11
72) Which of the following is not a fused-ring heterocycle?
A) purine
B) pyrimidine
C) benzofuran
D) indole
E) quinoline
Answer: B
Diff: 2
Section: 16.12
-
20
73) Classify the compound below as aromatic, antiaromatic, or nonaromatic. Assume planarity
of the network.
Answer: aromatic
Diff: 2
Section: 16.12
74) Provide the structure of indole.
Answer:
Diff: 3
Section: 16.12
75) How many distinct trichlorobenzene isomers are possible?
A) 2
B) 3
C) 4
D) 5
E) 6
Answer: B
Diff: 1
Section: 16.13
76) Which of the following is another accepted name for methyl phenyl ketone?
A) anisole
B) cresol
C) acetophenone
D) benzophenone
E) cresone
Answer: C
Diff: 1
Section: 16.13
-
21
77) Which of the following is also an acceptable name for 3-nitrophenol?
A) o-nitrophenol
B) m-nitrophenol
C) p-nitrophenol
D) 3-cresol
E) hydroquinone
Answer: B
Diff: 1
Section: 16.13
78) Which of the following is also an acceptable name for 1,3,5-trimethylbenzene?
A) styrene
B) mesitylene
C) cumene
D) cymene
E) 1,3,5-xylene
Answer: B
Diff: 2
Section: 16.13
79) Provide an acceptable name for the compound below.
Answer: 1,3,5-trinitrobenzene
Diff: 1
Section: 16.13
80) Provide the structure of m-xylene.
Answer:
Diff: 2
Section: 16.13
-
22
81) Provide the structure of o-toluic acid.
Answer:
Diff: 2
Section: 16.13
82) Provide the structure of 2,5-dichlorophenol.
Answer:
Diff: 2
Section: 16.13
83) Provide the structure of o-chlorotoluene.
Answer:
Diff: 2
Section: 16.13
84) Provide the structure of p-aminobenzoic acid.
Answer:
Diff: 2
Section: 16.13
-
23
85) Provide the structure of 2,4,6-trichlorophenol.
Answer:
Diff: 2
Section: 16.13
86) Provide the structure of m-iodobenzoic acid.
Answer:
Diff: 2
Section: 16.13
87) Provide the name of the compound shown below.
Answer: o-chlorobenzoic zcid or 2-chlorobenzoic acid
Diff: 2
Section: 16.13
-
24
88) Provide the name of the compound shown below.
Answer: m-iodobenzaldehyde or 3-iodobenzaldehyde
Diff: 2
Section: 16.13
89) Provide an acceptable name for the compound below.
Answer: para-dichlorobenzene or 1,4-dichlorobenzene
Diff: 1
Section: 16.13
90) Provide an acceptable name for the compound below.
Answer: ortho-xylene or 1,2-dimethylbenzene
Diff: 1
Section: 16.13
91) Provide an acceptable name for the compound below.
Answer: aniline or aminobenzene or benzeneamine
Diff: 2
Section: 16.13
-
25
92) Provide an acceptable name for the compound below.
Answer: 2,4-dinitrotoluene
Diff: 2
Section: 16.13
93) Provide the structure of m-nitrophenol.
Answer:
Diff: 2
Section: 16.13
94) Provide the structure of anisole.
Answer:
Diff: 2
Section: 16.13
95) Provide the structure of o-bromostyrene.
Answer:
Diff: 2
Section: 16.13
96) Provide the structure of 2-bromo-4-chlorobenzoic acid.
Answer:
Diff: 2
Section: 16.13
-
26
97) Provide the structure of 4-isopropylbenzaldehyde.
Answer:
Diff: 2
Section: 16.13
98) Provide an acceptable name for PhSO3H.
Answer: benzenesulfonic acid
Diff: 2
Section: 16.13
99) Provide an acceptable name for the compound below.
Answer: imidazole
Diff: 3
Section: 16.13
100) Which of the following compounds has the lowest boiling point?
A) 1,2,3-trichlorobenzene
B) 1,2,4-tirchlorobenzene
C) p-dichlorobenzene
D) m-dichlorobenzene
E) o-dichlorobenzene
Answer: C
Diff: 2
Section: 16.14
101) Which of the following compound has the highest melting point?
A) benzene
B) toluene
C) o-dichlorobenzene
D) m-dichlorobenzene
E) p-dichlorobenzene
Answer: E
Diff: 2
Section: 16.14
-
27
102) In the UV-visible spectra of the following compounds, in which does lambda max appear at
the highest wavelength?
A) 3-phenylpropene
B) 1-phenylpropene
C) benzene
D) n-octylbenzene
E) isopropylbenzene
Answer: B
Diff: 1
Section: 16.15
103) In the proton NMR, in what region of the spectrum does one typically observe hydrogens
bound to the aromatic ring?
A) 1.0-1.5 ppm
B) 2.0-3.0 ppm
C) 4.5-5.5 ppm
D) 7.0-8.0 ppm
E) 9.0-10.0 ppm
Answer: D
Diff: 2
Section: 16.15
104) In the carbon NMR, in what region of the spectrum does one typically observe carbons
which are part of the aromatic ring?
A) -10-0 ppm
B) 40-60 ppm
C) 80-100 ppm
D) 120-150 ppm
E) 200-220 ppm
Answer: D
Diff: 2
Section: 16.15
105) Which of the following compounds has the most signals in the noise-decoupled 13C NMR
spectrum?
A) o-dibromobenzene
B) m-dibromobenzene
C) p-dibromobenzene
D) 1,3,5-tribromobenzene
E) 1,2,3,4-tetrabromobenzene
Answer: B
Diff: 2
Section: 16.15
-
28
107) How many peaks are in the proton spin decoupled 13C NMR spectrum of p-
dichlorobenzene?
A) 2
B) 3
C) 4
D) 5
E) 6
Answer: A
Diff: 2
Section: 16.15
108) How many peaks are in the proton spin decoupled 13C NMR spectrum of 1,3,5-
trinitrobenzene?
A) 1
B) 2
C) 3
D) 4
E) 6
Answer: B
Diff: 2
Section: 16.15
109) How many peaks are in the proton spin decoupled 13C NMR spectrum of 1,2,3-
trichlorobenzene?
A) 1
B) 2
C) 3
D) 4
E) 6
Answer: D
Diff: 2
Section: 16.15
-
29
110) The IR spectrum of m-xylene contains stretches which are characteristic of most aromatic
hydrocarbons. List the peaks (in cm-1) associated with the aromatic C=C stretch and the
aromatic CH stretch.
Answer: C=C: around 1600 cm-1
CH: just above 3000 cm-1 (usually around 3030 cm-1) Diff: 2
Section: 16.15
111) How might one distinguish the isomers of trimethylbenzene by noise-decoupled 13C NMR?
Answer: 1,3,5-trimethylbenzene: 3 signals
1,2,4-trimethylbenzene: 9 signals
1,2,3-trimethylbenzene: 6 signals
Diff: 2
Section: 16.15