Aromatic Polycyclic Hydrocarbons

A major group of unsaturated Cyclic Hydrocarbons containing two or more rings. The vast number of compounds of this important group, derived chiefly from Petroleum and Coal Tar, are rather highly reactive and chemically versatile. The name is due to the strong and not unpleasant Odor characteristic of most substances of this Nature. (From Hawley's Condensed Chemical Dictionary, 12th ed, p96)