Chapter 14: Aromatic Compounds
Learning Objectives:
1. Recognize and distinguish between aromatic and antiaromatic compounds by their
structures.
2. Know the properties of aromatic and antiaromatic compounds, and the chemical
consequences of aromaticity.
3. Recognize and be able to write the mechanism of electrophilic aromatic substitution
4. Be able to outline the completed electrophilic aromatic substitution reactions of the
following types: halogenation, nitration, sulfonation, and Friedel-Crafts acylation &
alkylation
Sections:
14.1
14.2
14.3
14.4
14.5
14.6
14.7
14.8
14.9
14.10
14.11
14.12
14.13
14.14
14.15
14.16
14.17
14.18
14.19
Armoatic Compounds Are Unusually Stable
The Two Criteria for Aromaticity*
Applying the Criteria for Aromaticity
Aromatic Heterocyclic Compounds
Some Chemical Consequences of Aromaticity*
Antiaromaticity
A Molecular Orbital Description of Aromaticity and Antiaromaticity
Nomenclature of Monosubstituted Benzenes
How Benzene Reacts*
The General Mechanism for Electrophilic Aromatic Substitution Reactions*
Halogenation of Benzene*
Nitration of Benzene*
Sulfonation of Benzene*
Friedel-Crafts Acylation of Benzene*
Friedel-Crafts Alkylation of Benzene*
Alkylation of Benzene by Acylation-Reduction*
Using Coupling Reaction to Alkylate Benzene#
It Is Important to Have More Than One Way to Carry Out a Reaction
How Some Substituents Can Be Chemically Changed*
* Sections that will be focused
#
Sections that will be skipped
Recommended additional problems
14.30 – 14.49
1
Class Note
14.1
Armoatic Compounds Are Unusually Stable
H2
Ni
H = -28.6 kcal/mol
+ 3H2 cyclohexatriene
(hypothetical)
36 kcal/mol
+ 3H2
-85.8 kcal/mol
(-28.6x3)
Energy
+ H2
-49.8 kcal/mol
-28.6 kcal/mol
2
14.2
The Two Criteria for Aromaticity* and 14.6
Antiaromaticity
A. Cyclic molecule
B. Every atom has p orbital
C. Planar molecule
D. Comply with 4n+2 rule (as compared with 4n rule)
E. Consequence of aromaticity
3
14.3
Applying the Criteria for Aromaticity and 14.4
Compounds
4
Aromatic Heterocyclic
H
N
H
N
O
S
N
O
S
H
N
N
N
N
H
N
CH3
OH
H
N
N
N
CH2
CH2
O
OH
O
OH
H
N
N
5
14.5
Some Chemical Consequences of Aromaticity*
A. Acidity of protons
H H
H
H
B. Aromaticity on leaving group
Br
Br
6
C. Aromaticity on dipole moment (polarity)
O
O
7
14.7
A Molecular Orbital Description of Aromaticity and Antiaromaticity
8
14.8
Nomenclature of Monosubstituted Benzenes
Cl
NO2
Br
CH3
SO3H
NH2
OH
OCH3
CH3
CHO
CO2H
As substituent:
CH2
9
CHCH3
14.9
How Benzene Reacts* and 14.10
Aromatic Substitution Reactions*
The General Mechanism for Electrophilic
Addition vs. Substitution
Electrophilic Aromatic Substitution vs. Nucleophilic Aromatic Substitution
10
A. General Mechanism of Electrophilic Aromatic Substitution
B. Reaction coordinate diagram
11
14.11
Halogenation of Benzene*
14.12
Nitration of Benzene*
12
14.13
Sulfonation of Benzene*
14.14
Friedel-Crafts Acylation of Benzene*
13
14.15
Friedel-Crafts Alkylation of Benzene*
Result from carbocation migration
14
14.16 Alkylation of Benzene by Acylation-Reduction* and 14.18
Have More Than One Way to Carry Out a Reaction
A. Clemmensen reduction
B. Wolff-Kishner reduction
15
It Is Important to
14.19
How Some Substituents Can Be Chemically Changed*
A. Reactions of Alkyl Substituents
tert-BuO
Br
NBS
OH
peroxide
or h
CN
16
H2, Pt
N
O
H2, Pt
H2, Pt
B. Oxidations of Alkyl Substituents
1. KMnO4, heat (reflux)
2. H+
Na2Cr2O7, H+, heat
17
Na2Cr2O7, H+, heat
Na2Cr2O7, H+, heat
Na2Cr2O7, H+, heat
OH
MnO2
(no heating needed)
OH
Na2Cr2O7, H+, heat
18
C. Reduction of Nitro Group
NO2
H2, Pt
NO2
Sn, HCl
NO2
Fe, HCl
19