4.6.3 General properties of aromatic compounds
Aromatic compounds have the following general properties.
(a) They have a high degree of unsaturation, but are resistant to addition
reactions.
(b) They favour electrophilic substitution reactions.
(c) These compounds are unusually stable.
(d) They have a low heat of hydrogenation and low heat of combustion.
(e) They are cyclic compounds.
(f) These compounds are flat and planar.
4.6.4 Classification of aromatic compounds
Benzene and its monocylic derivatives
CH 3
OH
NH 2
Toluene
Phenol
Aniline
Benzene
Polycyclic benzenoids These aromatic compounds have two or more
benzene rings fused together, e.g. naphthalene and anthracene.
Naphthalene
Anthracene
Nonbenzenoids These compounds generally have two or more rings fused
together, but none of the rings is a benzene structure, and they conform to
Hu ¨ckel’s rule, i.e. they have ð4n þ 2Þ p electrons, and are aromatic
compounds, e.g. azulene.
Azulene
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Aromatic compounds have the following general properties.
(a) They have a high degree of unsaturation, but are resistant to addition
reactions.
(b) They favour electrophilic substitution reactions.
(c) These compounds are unusually stable.
(d) They have a low heat of hydrogenation and low heat of combustion.
(e) They are cyclic compounds.
(f) These compounds are flat and planar.
4.6.4 Classification of aromatic compounds
Benzene and its monocylic derivatives
CH 3
OH
NH 2
Toluene
Phenol
Aniline
Benzene
Polycyclic benzenoids These aromatic compounds have two or more
benzene rings fused together, e.g. naphthalene and anthracene.
Naphthalene
Anthracene
Nonbenzenoids These compounds generally have two or more rings fused
together, but none of the rings is a benzene structure, and they conform to
Hu ¨ckel’s rule, i.e. they have ð4n þ 2Þ p electrons, and are aromatic
compounds, e.g. azulene.
Azulene
4.6 AROMATIC COMPOUNDS AND THEIR DERIVATIVES
113