Deck 16: Chemistry of Benzene: Electrophilic Aromatic Substitution

Question 1

Exhibit 16-2
Consider the Friedel-Crafts alkylation reaction below to answer the following question(s):
Refer to Exhibit 16-2.What is the role of the AlCl₃ in the reaction?

Answer 1

The AlCl₃ is a Lewis acid catalyst that assists in the ionization of the alkyl halide to give the carbocation electrophile.

Question 2

Exhibit 16-1
MATCH a structure or term from the following list with each description below.Place the letter of the structure or term in the blank to the left of the description.
a.benzyne
e.⁺NO
b.⁺NO₂
f.Meisenheimer complex
c.R₃C⁺
g. d.electron-donating
h.electron-withdrawing
i.F-TEDA-BF₄
______ The reactive electrophile in Friedel-Crafts acylation reactions.

Answer 2

g

Question 3

Exhibit 16-1
MATCH a structure or term from the following list with each description below.Place the letter of the structure or term in the blank to the left of the description.
a.benzyne
e.⁺NO
b.⁺NO₂
f.Meisenheimer complex
c.R₃C⁺
g. d.electron-donating
h.electron-withdrawing
i.F-TEDA-BF₄
______ The electrophile in aromatic nitration.

Answer 3

b

Question 4

Exhibit 16-1
MATCH a structure or term from the following list with each description below.Place the letter of the structure or term in the blank to the left of the description.
a.benzyne
e.⁺NO
b.⁺NO₂
f.Meisenheimer complex
c.R₃C⁺
g. d.electron-donating
h.electron-withdrawing
i.F-TEDA-BF₄
______ Groups which activate aromatic rings towards electrophilic substitution.

Question 5

Exhibit 16-3
Consider the data below to answer the following question(s).
The −NH₂ group is listed in our textbook as the strongest o,p-directing activator in electrophilic aromatic substitution reactions.However,when aniline is subjected to standard nitration conditions poor yields of m-nitroaniline result.
Refer to Exhibit 16-3.Draw all the resonance forms of aniline showing the electron-donating effect of the −NH₂ substituent.

Question 6

Aniline reacts with nitrous acid,HNO₂,to yield a stable diazonium salt.This diazonium salt undergoes electrophilic aromatic substitution on activated aromatic rings to yield brightly colored azo compounds that are widely used as dyes.The intermediate structures for the mechanism of this reaction are given below.Show all electron flow with arrows for this mechanism on the structures provided.

Question 7

Exhibit 16-2
Consider the Friedel-Crafts alkylation reaction below to answer the following question(s):
Refer to Exhibit 16-2.Write the complete stepwise mechanism for this reaction.Show all electron flow with arrows and include all intermediate structures.

Question 8

Exhibit 16-6
To answer the following question(s),refer to the data below:
Isobutylbenzene is the starting material for the industrial synthesis of the NSAID,ibuprofen.
Refer to Exhibit 16-6.Propose a synthesis for isobutylbenzene which avoids the problems of direct Friedel-Crafts alkylation.

Question 9

Exhibit 16-1
MATCH a structure or term from the following list with each description below.Place the letter of the structure or term in the blank to the left of the description.
a.benzyne
e.⁺NO
b.⁺NO₂
f.Meisenheimer complex
c.R₃C⁺
g. d.electron-donating
h.electron-withdrawing
i.F-TEDA-BF₄
______ Groups which activate aromatic rings towards nucleophilic substitution.

Question 10

Would you expect (nitromethyl)benzene to be more reactive or less reactive than toluene toward electrophilic substitution? Explain.

Question 11

Exhibit 16-2
Consider the Friedel-Crafts alkylation reaction below to answer the following question(s):
Refer to Exhibit 16-2.Draw the structure of the electrophilic intermediate in this reaction.

Question 12

Exhibit 16-1
MATCH a structure or term from the following list with each description below.Place the letter of the structure or term in the blank to the left of the description.
a.benzyne
e.⁺NO
b.⁺NO₂
f.Meisenheimer complex
c.R₃C⁺
g. d.electron-donating
h.electron-withdrawing
i.F-TEDA-BF₄
__________Source of F⁺ in fluorination reactions.

Question 13

Exhibit 16-1
MATCH a structure or term from the following list with each description below.Place the letter of the structure or term in the blank to the left of the description.
a.benzyne
e.⁺NO
b.⁺NO₂
f.Meisenheimer complex
c.R₃C⁺
g. d.electron-donating
h.electron-withdrawing
i.F-TEDA-BF₄
______ Intermediate in the elimination-addition mechanism of nucleophilic aromatic substitution.

Question 14

Exhibit 16-7
Consider the reaction below to answer the following question(s).
Refer to Exhibit 16-7.The Lewis acid catalyst in the reaction is:

Question 15

Exhibit 16-6
To answer the following question(s),refer to the data below:
Isobutylbenzene is the starting material for the industrial synthesis of the NSAID,ibuprofen.
Refer to Exhibit 16-6.Attempts to prepare isobutylbenzene by direct Friedel-Crafts alkylation of benzene result in tert-butylbenzene as the major product.Write the complete stepwise mechanism for this reaction,showing all electron flow with arrows and showing all intermediate structures.

Question 16

Exhibit 16-4
Consider the reaction below to answer the following question(s).
Refer to Exhibit 16-4.Draw resonance structures for the intermediate carbocation that explain the directing effect of the −Br.

Question 17

Exhibit 16-7
Consider the reaction below to answer the following question(s).
Refer to Exhibit 16-7.This reaction proceeds _____ (faster or slower) than benzene.

Question 18

Exhibit 16-7
Consider the reaction below to answer the following question(s).
Refer to Exhibit 16-7.The nucleophile in the reaction is:

Question 19

Exhibit 16-3
Consider the data below to answer the following question(s).
The −NH₂ group is listed in our textbook as the strongest o,p-directing activator in electrophilic aromatic substitution reactions.However,when aniline is subjected to standard nitration conditions poor yields of m-nitroaniline result.
Refer to Exhibit 16-3.Clearly,the reaction conditions are influencing the directing effect of the −NH₂ group.Explain why this occurs,using both words and structures.

Question 20

Exhibit 16-4
Consider the reaction below to answer the following question(s).
Refer to Exhibit 16-4.Write the complete stepwise mechanism for the formation of the ortho product.Show all intermediate structures and show all electron flow with arrows.

Question 21

Which of the following is an ortho- and para- director and a deactivator?

A)-NO₂
B)-F
C)-CN
D)-CH₂CH₃
E)none of these

Question 22

Which of the following could successfully undergo a Friedel-Crafts alkylation? Assume an appropriate catalyst.

A)chlorobenzene reacting with benzene
B)2-chloroethene reacting with benzene
C)2-chloropropane reacting with benzaldehyde
D)2-chlorobutane reacting with benzene

Question 23

Arrange the following compounds in order of increasing reactivity to electrophilic aromatic substitution. bromobenzene nitrobenzene benzene phenol

A)phenol < benzene < bromobenzene < nitrobenzene
B)bromobenzene < nitrobenzene < benzene < phenol
C)nitrobenzene < bromobenene < benzene < phenol
D)nitrobenzene < benzene < bromobenzene < phenol

Question 24

The following reaction proceeds by an intramolecular nucleophilic aromatic substitution mechanism.Write the complete stepwise mechanism,showing all intermediate structures and all electron flow with arrows.

Question 25

Exhibit 16-7
Consider the reaction below to answer the following question(s).
Refer to Exhibit 16-7.Draw the structure of product D.

Question 26

On the structural intermediates below,show all electron flow with arrows for the nucleophilic aromatic substitution reaction of p-nitrochlorobenzene with KOH.

Question 27

Which of the following is a meta-deactivating group?

A)-CO₂H
B)-I
C)-OH
D)-CH₃

Question 28

Which of the following is an ortho- and para- director?

A)-NO₂
B)-NH₂
C)-CN
D)-CO₂CH₃

Question 29

Tetracyclone is often used to trap benzynes as Diels-Alder adducts.What is the structure of the Diels-Alder adduct that results when benzyne is trapped by tetracyclone?

Question 30

Which of the following is a meta- director?

A)-OH
B)-Br
C)-CH₂CH₂CH₃
D)-COCH₃