Illustrated Glossary of Organic Chemistry

Polycyclic aromatic hydrocarbon (PAH): An aromatic hydrocarbon whose molecular structure contains two or more fused benzene rings. Some representative examples are shown below.

Triphenylmethane		Fluorene

Triphenylmethane and fluorene are both hydrocarbons with two or more benzene rings, but neither are classified as polycyclic aromatic hydrocarbons because they both lack fused benzene rings.