In organic chemistry, a cyclic compound is one whose molecules consist of three or more atoms joined in a closed ring. A polycyclic compound is one whose molecules contain two or more rings joined to each other. Environmentally, the most important polycyclic organic compounds are the polycyclic aromatic hydrocarbons, also known as polynuclear aromatic hydrocarbons (PAHs). Some examples of polycyclic organic compounds include naphthalene, anthracene, pyrene, and the benzopyrenes. A number of polycyclic hydrocarbons pose hazards to human health. For example, benzo(a)pyrene from automobile exhaust and tobacco smoke is known to be a carcinogen.

See Also

Cigarette Smoke