An unsaturated hydrocarbon occurring in most essential oils and oleoresins of plants. The terpenes are based on the isoprene unit C5H8, and may be either acyclic or cyclic with one or more benzenoid groups. They are classified as monocyclic (dipentene), dicyclic (pinene), or acyclic (myrcene), according to the molecular structure. Many terpenes exhibit optical activity. Terpene derivatives (camphor, menthol, terpineol, borneol, geraniol, etc.) are called terpenoids; many are alcohols. See polyterpene resin.
