OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
Chapter 16 – Chemistry of Benzene: Electrophilic Aromatic Substitution
Solutions to Problems
16.1
16.2
The π electrons of benzene attack the fluorine of F-TEDA-BF4, and the nonaromatic
intermediate loses –H to give the fluorinated product.
16.3
Chlorination at either position “a” of o-xylene yields product A, and chlorination at either
position “b” yields product B.
Three products might be expected to form on chlorination of m–xylene.
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Only one product results from chlorination of p–xylene because all sites are equivalent.
16.4
Benzene can be protonated by strong acids. The resulting intermediate can lose either
deuterium or hydrogen. If –H is lost, deuterated benzene is produced. Attack by
deuterium can occur at all positions of the ring and leads to eventual replacement of all
hydrogens by deuterium. Only the first step is shown.
16.5 Carbocation rearrangements of alkyl halides occur (1) if the initial carbocation is primary
or secondary, and (2) if it is possible for the initial carbocation to rearrange to a more
stable secondary or tertiary cation.
+
(a) Although CH3 C H 2 is a primary carbocation, it can’t rearrange to a more
stable cation.
(b) CH3CH2CH(Cl)CH3 forms a secondary carbocation that doesn’t rearrange.
+ +
(c) CH3CH 2 C H 2 rearranges to the more stable CH3 C HCH3CH3CHCH3 .
+ +
(d) ( CH3 )3 C C H 2 (primary) undergoes an alkyl shift to yield ( CH3 )2 C CH 2CH3
(tertiary).
(e) The cyclohexyl carbocation doesn’t rearrange.
In summary:
No rearrangement: (a) CH3CH2Cl, (b) CH3CH2CH(Cl)CH3, (e) chlorocyclohexane
Rearrangement: (c) CH3CH2CH2Cl, (d) (CH3)3CCH2Cl
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,OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
16.6
The isobutyl carbocation, initially formed when 1-chloro-2-methylpropane and AlCl3
react, rearranges via a hydride shift to give the more stable tert–butyl carbocation, which
can then alkylate benzene to form tert–butylbenzene.
16.7 To identify the carboxylic acid chloride used in the Friedel–Crafts acylation of benzene,
break the bond between benzene and the ketone carbon and replace it with a –Cl.
(a)
(b)
16.8 Use Figure 16.12 to find the activating and deactivating effects of groups.
Most Reactive Least Reactive
(a) Phenol > toluene > benzene > nitrobenzene
(b) Phenol > benzene > chlorobenzene > benzoic acid
(c) Aniline > benzene > bromobenzene > benzaldehyde
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16.9 Refer to Figure 16.12 in the text for the directing effects of substituents. You should
memorize the effects of the most important groups. As in Worked Example 16.2, identify
the directing effect of the substituent, and draw the product.
(a)
Even though bromine is a deactivator, it is an ortho-para director.
(b)
The –NO2 group is a meta-director.
(c)
(d)
No catalyst is necessary because aniline is highly activating.
16.10 An acyl substituent is deactivating. Once an aromatic ring has been acylated, it is much less
reactive to further substitution. An alkyl substituent is activating, however, so an alkyl-
substituted ring is more reactive than an unsubstituted ring, and polysubstitution occurs
readily.
16.11 (Trifluoromethyl)benzene is less reactive toward electrophilic substitution than toluene. The
electronegativity of the three fluorine atoms causes the trifluoromethyl group to be electron-
withdrawing and deactivating toward electrophilic substitution. The electrostatic potential map
shows that the aromatic ring of (trifluoromethyl)benzene is more electron-poor, and thus less
reactive, than the ring of toluene (red).
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Chapter 16 – Chemistry of Benzene: Electrophilic Aromatic Substitution
Solutions to Problems
16.1
16.2
The π electrons of benzene attack the fluorine of F-TEDA-BF4, and the nonaromatic
intermediate loses –H to give the fluorinated product.
16.3
Chlorination at either position “a” of o-xylene yields product A, and chlorination at either
position “b” yields product B.
Three products might be expected to form on chlorination of m–xylene.
1 10/3/2023
, OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
Only one product results from chlorination of p–xylene because all sites are equivalent.
16.4
Benzene can be protonated by strong acids. The resulting intermediate can lose either
deuterium or hydrogen. If –H is lost, deuterated benzene is produced. Attack by
deuterium can occur at all positions of the ring and leads to eventual replacement of all
hydrogens by deuterium. Only the first step is shown.
16.5 Carbocation rearrangements of alkyl halides occur (1) if the initial carbocation is primary
or secondary, and (2) if it is possible for the initial carbocation to rearrange to a more
stable secondary or tertiary cation.
+
(a) Although CH3 C H 2 is a primary carbocation, it can’t rearrange to a more
stable cation.
(b) CH3CH2CH(Cl)CH3 forms a secondary carbocation that doesn’t rearrange.
+ +
(c) CH3CH 2 C H 2 rearranges to the more stable CH3 C HCH3CH3CHCH3 .
+ +
(d) ( CH3 )3 C C H 2 (primary) undergoes an alkyl shift to yield ( CH3 )2 C CH 2CH3
(tertiary).
(e) The cyclohexyl carbocation doesn’t rearrange.
In summary:
No rearrangement: (a) CH3CH2Cl, (b) CH3CH2CH(Cl)CH3, (e) chlorocyclohexane
Rearrangement: (c) CH3CH2CH2Cl, (d) (CH3)3CCH2Cl
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,OpenStax Organic Chemistry: A Tenth Edition Student Solutions Manual
16.6
The isobutyl carbocation, initially formed when 1-chloro-2-methylpropane and AlCl3
react, rearranges via a hydride shift to give the more stable tert–butyl carbocation, which
can then alkylate benzene to form tert–butylbenzene.
16.7 To identify the carboxylic acid chloride used in the Friedel–Crafts acylation of benzene,
break the bond between benzene and the ketone carbon and replace it with a –Cl.
(a)
(b)
16.8 Use Figure 16.12 to find the activating and deactivating effects of groups.
Most Reactive Least Reactive
(a) Phenol > toluene > benzene > nitrobenzene
(b) Phenol > benzene > chlorobenzene > benzoic acid
(c) Aniline > benzene > bromobenzene > benzaldehyde
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16.9 Refer to Figure 16.12 in the text for the directing effects of substituents. You should
memorize the effects of the most important groups. As in Worked Example 16.2, identify
the directing effect of the substituent, and draw the product.
(a)
Even though bromine is a deactivator, it is an ortho-para director.
(b)
The –NO2 group is a meta-director.
(c)
(d)
No catalyst is necessary because aniline is highly activating.
16.10 An acyl substituent is deactivating. Once an aromatic ring has been acylated, it is much less
reactive to further substitution. An alkyl substituent is activating, however, so an alkyl-
substituted ring is more reactive than an unsubstituted ring, and polysubstitution occurs
readily.
16.11 (Trifluoromethyl)benzene is less reactive toward electrophilic substitution than toluene. The
electronegativity of the three fluorine atoms causes the trifluoromethyl group to be electron-
withdrawing and deactivating toward electrophilic substitution. The electrostatic potential map
shows that the aromatic ring of (trifluoromethyl)benzene is more electron-poor, and thus less
reactive, than the ring of toluene (red).
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