Essential Organic Chemistry (Bruice)
Essential Organic Chemistry (Bruice)
Chapter 7
Essential Organic Chemistry (Bruice)
Chapter 7Aromaticity: Reactions of Benzene and Substituted
Benzenes
1)
The following molecule is not aromatic. Why?
Answer:
It does not have an odd number of pairs of pi electrons (i.e.,
it does not obey Huckel's rule) and it is not planar.
Section: 7.1
2)
Is the following molecule aromatic? Explain.
Answer:
Yes, it is aromatic since the carbon framework for the system of
the molecule is planar, monocyclic with 5 pairs of electrons.
Section: 7.1
3)
Is the following molecule aromatic? Explain.
Answer:
No, it is not aromatic since the molecule is not a conjugated
system.
Section: 7.1
4)
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.
Section: 7.1
5)
Aromatic molecules contain __________ electrons.
A)
no
B)
4n + 2 (with n being an integer)
C)
4n + 2 (with n being 0.5)
D)
4n (with n an integer)
E)
unpaired
Answer:
B
Section: 7.1
6)
Which of the following is an aromatic hydrocarbon?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
C
Section: 7.2
7)
Which of the following is aromatic?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
C
Section: 7.2
8)
Which of the following is aromatic?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
B
Section: 7.2
9)
Cyclic hydrocarbons which can be represented as structures
containing alternating single and double bonds are called
__________.
Answer:
annulenes
Section: 7.2
10)
Which of the structures below would be aromatic?
A)
I and IV
B)
I, III, and IV
C)
III and IV
D)
II
Answer:
C
Section: 7.2
11)
Which of the following is aromatic?
A)
cyclopentadienyl cation
B)
1,3-cyclohexadiene
C)
cyclobutenyl anion
D)
1,3,5-hexatriene
E)
cycloheptatrienyl cation
Answer:
E
Section: 7.2
12)
Which of the following compounds is aromatic?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
D
Section: 7.3
13)
Which of the following is aromatic?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
A
Section: 7.3
14)
Provide the structure of the biologically significant
heterocycle purine.
Answer:
Section: 7.3
15)
What is the name of the following structure?
Answer:
furan
Section: 7.3
16)
What is the name of the following structure?
Answer:
pyridine
Section: 7.3
17)
What is the name of the following structure?
Answer:
pyrrole
Section: 7.3
18)
Provide the structure of the biologically significant
heterocycle pyrimidine.
Answer:
Section: 7.3
19)
Provide the structure of indole.
Answer:
Section: 7.3
20)
Provide the structure of anisole.
Answer:
Section: 7.4
21)
Provide the structure of benzenesulfonic acid.
Answer:
Section: 7.4
22)
Provide the structure of dibenzyl ether.
Answer:
Section: 7.4
23)
What is the structure of phenol?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
D
Section: 7.4
24)
Provide the structure of benzoic acid.
Answer:
Section: 7.4
25)
Why does benzene undergo electrophilic substitution rather than
electrophilic addition?
Answer:
When benzene undergoes electrophilic substitution, the product
retains the stability associated with an aromatic system. This
stability is lost in electrophilic addition because the product is
not aromatic.
Section: 7.5
26)
Discuss the role of benzene in the first step of an
electrophilic aromatic substitution reaction.
Answer:
Benzene is a nucleophile, i.e. the electrons of the benzene ring
attack the electrophile and a carbocation results.
Section: 7.5
27)
Describe how the aromatic character of the benzene ring is
re-created from the nonaromatic carbocation intermediate during an
electrophilic aromatic substitution reaction.
Answer:
An electron pair donating (Lewis base) species attacks the
hydrogen adjacent to the carbocation then the electrons between
this hydrogen and its carbon are donated to the ring to re-create
the aromatic benzene ring.
Section: 7.5
28)
Which of the following is not a correct statement about the
electrophilic substitution mechanism of benzene?
A)
Benzene functions as a nucleophile.
B)
Formation of a carbocation intermediate is the rate-determining
step.
C)
The carbocation intermediate contains an sp3 hybridized carbon
in the ring.
D)
The addition product is a frequently observed minor product.
E)
Aromaticity is regained by loss of H+.
Answer:
D
Section: 7.5
29)
Which of the following is most likely to be the first step in
the general mechanism for electrophilic substitution reactions?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
B
Section: 7.6
30)
Provide the major resonance structures of the intermediate sigma
complex in the reaction of benzene with the generic electrophile
E+.
Answer:
Section: 7.6
31)
Which step in the general mechanism for electrophilic aromatic
substitution is rate-determining? Explain.
Answer:
The first step involves addition of the electrophile to benzene
to yield a nonaromatic cationic intermediate. The second step
involves the loss of H+ from this cationic intermediate to yield an
aromatic product. The rate-determining or slow step is the one in
which the aromatic reagent is converted into a much less stable
nonaromatic cation.
Section: 7.6
32)
In the bromination of benzene using Br2 and FeBr3, is the
intermediate carbocation aromatic? Explain.
Answer:
No, the carbocation is not aromatic since the ring contains an
sp3 center.
Section: 7.6 and 7.7
33)
Which of the following is one of the resonance contributors of
the intermediate produced in a Friedel-Crafts alkylation of
benzene?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
A
Section: 7.6 and 7.11
34)
Which of the following is the first step in the mechanism of
bromination?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
C
Section: 7.7
35)
Provide a detailed, stepwise mechanism for the reaction of
benzene with Br2 and FeBr3. Make sure to include the activating
reaction between Br2 and FeBr3 in your mechanism.
Answer:
Section: 7.7
36)
Bromination of benzene requires a Lewis acid catalyst while
bromination of cyclohexene does not. Explain this difference in
reactivity.
Answer:
An alkene is a better nucleophile than benzene, and thus the
Br-Br bond does not have to be weakened to form a better
electrophile before reaction.
Section: 7.7
37)
What purpose does FeCl3 serve in the electrophilic aromatic
substitution reaction between chlorine and benzene?
A)
It serves as a radical initiator to produce the chlorine radical
needed to propagate the chain reaction.
B)
It functions by destabilizing the carbocationic intermediate and
thereby increases the rate of H+ loss.
C)
It serves as a Lewis base catalyst by reacting with Cl2 to
generate chloride ions.
D)
It functions by destabilizing the benzene through formation of a
-complex.
E)
It serves as a Lewis acid catalyst by reacting with the Cl2 and
thereby activates it toward attack by benzene's electrons.
Answer:
E
Section: 7.7
38)
Explain the role of nitric acid and sulfuric acid in the first
step in the nitration of benzene.
Answer:
A hydrogen from sulfuric acid protonates the hydroxy group of
the nitric acid forming a molecule of water which is then a good
leaving group, thereby forming the nitronium ion (NO2+)(the
electrophile).
Section: 7.8
39)
Which of the following is the electrophile that attacks the
aromatic ring during nitration?
A)
NO2
B)
HNO3
C)
D)
E)
Answer:
D
Section: 7.8
40)
Which of the following is the electrophile that attacks the
aromatic ring during sulfonation?
A)
B)
C)
D)
H2SO4
E)
Answer:
A
Section: 7.9
41)
Which of the following is the electrophile that attacks the
aromatic ring during Friedel-Crafts acylation?
A)
B)
C)
D)
E)
AlCl3
Answer:
B
Section: 7.10
42)
What is the role of AlCl3 in Friedel-Crafts acylation of benzene
and Friedel-Crafts akylation of benzene?
Answer:
AlCl3 reacts with the acyl chloride in the acylation to give an
acylium ion and -AlCl4. AlCl3 reacts with the alkyl halide to give
a carbocation and -AlCl4.
Section: 7.10 and 7.11
43)
Which of the following is not a correct statement concerning the
Friedel-Crafts acylation of benzene?
A)
An alkyl group substitutes for a hydrogen.
B)
The benzene ring attacks an acylium ion.
C)
The acylium ion is resonance stabilized.
D)
The acylium ion is often produced from an acyl chloride.
E)
More than one equivalent of Lewis acid must be used.
Answer:
A
Section: 7.10
44)
What is the major product of the following Friedel-Crafts
alkylation?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
C
Section: 7.11
45)
What is the major organic product of the reaction between
benzene and isobutyl chloride in the presence of AlCl3?
A)
tert-butylbenzene
B)
isobutylbenzene
C)
n-butylbenzene
D)
chlorobenzene
E)
sec-butylbenzene
Answer:
A
Section: 7.11
46)
What is the name of the following compound?
A)
m-Bromomethylbenzene
B)
m-Bromotoluene
C)
3-Bromotoluene
D)
A and B
E)
B and C
Answer:
E
Section: 7.12
47)
What is the structure of 3-phenylpentane?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
E
Section: 7.12
48)
What is the name of the following compound?
A)
p-Dichlorobenzene
B)
1,4-Dichlorobenzene
C)
Phenyldichloride
D)
A and B
E)
B and C
Answer:
D
Section: 7.12
49)
What is the structure of p-toluidine?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
C
Section: 7.12
50)
What is the name of the following compound?
A)
o-nitro-m-bromotoluene
B)
3-bromo-6-nitrotoluene
C)
m-bromo-o-nitrotoluene
D)
5-bromo-2-nitrotoluene
E)
2-nitro-5-bromotoluene
Answer:
D
Section: 7.12
51)
The name 2,4,6-tribromobenzene is incorrect. Which of the
following is the correct name?
A)
tribromobenzene
B)
m,m-dibromobromobenzene
C)
3,5-dibromobromobenzene
D)
1,3,5-tribromobenzene
E)
m,m,m-tribromobenzene
Answer:
D
Section: 7.12
52)
What is the proper name of the compound below?
A)
1-phenoxyethane
B)
ethyl phenyl ether
C)
m-sec-butylhydroxybenzene
D)
o-butylhydroxybenzene
E)
m-butylphenol
Answer:
E
Section: 7.12
53)
Provide the best name for the organic compound below.
Answer:
o-propylphenol or 2-propylphenol
Section: 7.12
54)
Provide the best name for the organic compound below.
Answer:
m-toluidine
Section: 7.12
55)
Which of the following compounds reacts most slowly during
nitration?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
C
Section: 7.13
56)
Which of the following compounds reacts most rapidly during
nitration?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
D
Section: 7.13
57)
Which of the following substrates is an electron donating group
overall?
A)
Br
B)
C)
OCH3
D)
E)
CCl3
Answer:
C
Section: 7.13
58)
Which of the following substrates is an electron withdrawing
group overall?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
E
Section: 7.13
59)
Rank the following groups in order of increasing activating
power in electrophilic aromatic substitution reactions:
-OCH3, -OCOCH2CH3, -CH2CH3, -Br.
Answer:
-Br < -CH2CH3 < -OCOCH2CH3 < -OCH3
Section: 7.13
60)
Which of the following compounds reacts most rapidly with
HNO3/H2SO4?
A)
toluene
B)
anisole
C)
nitrobenzene
D)
benzonitrile
E)
fluorobenzene
Answer:
B
Section: 7.13
61)
List the following compounds in order of decreasing reactivity
toward electrophilic aromatic substitution: toluene, benzene,
fluorobenzene, nitrobenzene, phenol.
Answer:
phenol > toluene > benzene > fluorobenzene >
nitrobenzene
Section: 7.13
62)
Which of the following substituents acts as a moderate activator
and o/p director in electrophilic aromatic substitution
reactions?
A)
-Br
B)
-SO3H
C)
-CO2H
D)
-NHC(=O)R
E)
-CHO
Answer:
D
Section: 7.13
63)
Which of the following structures is the most important
contributor to the resonance hybrid formed when toluene undergoes
para nitration?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
A
Section: 7.14
64)
Which of the following structures is the most important
contributor to the resonance hybrid formed when anisole undergoes
o-bromination?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
A
Section: 7.14
65)
What is the major product of the following reaction?
A)
I
B)
II
C)
III
D)
IV
E)
V
Answer:
C
Section: 7.14
66)
In electrophilic aromatic substitution reactions a chlorine
substituent:
A)
is a deactivator and a m-director.
B)
is a deactivator and an o,p-director.
C)
is an activator and a m-director.
D)
is an activator and an o,p-director.
E)
none of the above
Answer:
B
Section: 7.14
67)
Draw the four major resonance structures of the carbocation
intermediate in the reaction of anisole with HNO3/H2SO4 to yield
p-nitroanisole.
Answer:
Section: 7.14
68)
Draw the three major resonance structures of the carbocation
intermediate in the reaction of acetophenone with HNO3/H2SO4 to
yield o-nitroacetophenone. Circle the resonance form which is less
stable than the other two.
Answer:
Section: 7.14
69)
Compare the effect of electron withdrawing group on an alcohol
relative to that of an electron donating group on an alcohol.
Answer:
An electron withdrawing group stabilizes a base and increases
the strength of its conjugate acid while an electron donating group
destabilizes a base and decreases the strength of its conjugate
acid. Thus electron withdrawing groups on an alcohol will increase
the acidity of the alcohol.
Section: 7.15
70)
List the following compounds in order of decreasing
basicity.
Answer:
Section: 7.15
71)
List the following compounds in order of decreasing acidity.
Answer:
Section: 7.15