Arenes

In early days of organic chemistry, the word aromatic was used to describe fragrant substances such as benzene( from coal distillate), benzaldehyde( from peaches, cherries and almonds), toluene ( from Tolu balsam).
Aromatic compounds show chemical behavior quite different from the alifatic compounds we have studied to this point.
Many compounds isolated from natural sources are aromatic in part. Steroidal hormone estrone and the well-known analgesic morphine have aromatic rings. Many synthetic drugs are also aromatic in part; the tranquilizer diazepam ( Valium) is an example.
Benzene should be handled cautiously if used as a laboratory solvent because it can cause bone marrow depression and consequent leukopenia( lowered white blood cell count) on prolonged exposure.