| We know the two
homologous series of unsaturated hydrocarbons,
the alkenes and the alkynes. These are both
families of straight chain or aliphatic hydrocarbons.
The group of hydrocarbons we are now going on
to consider do not have straight–chain
or branched molecules – they have a ring
structure. They are called the aromatic hydrocarbons.
The name 'aromatic' suggests a group of
sweetly perfumed chemicals, and it originates
from a time when many of the known members of
the family had pleasant smells. As chemists
discovered more and more 'aromatic' hydrocarbons,
they found that many other members of the group
smelled very unpleasant indeed. Our modern understanding
of the family tells us that many of these compounds
are toxic or carcinogenic (cancer causing),
so inhaling the vapour regardless of the smell
is not to be recommended. However, the historical
name has been retained for the group, and today
we are aware that the name refers to a family
of organic compounds linked by common structure
rather than by common smell. The systematic
name for the aromatic hydrocarbons is the arenes. |
