Terpenes are a class of natural products composed of compounds with the formula (C5H8)n. These unsaturated hydrocarbons consist of more than 30,000 compounds and are mainly produced by plants, especially conifers.
Terpenes are further classified by carbon number: Monoterpenes (C10), Sesquiterpenes (C15), Diterpenes (C20), as examples. The terpene alpha-pinene is a key component of the general solvent, turpentine.
The term « terpene » was coined in 1866 by the German chemist August Kekulé, who coined the term « terpene » to refer to any hydrocarbon with the molecular formula C10H16, of which camphene was one. In the past, many hydrocarbons with the molecular formula C10H16 were called « camphene », but many other hydrocarbons of the same composition had other names. Kekulé coined the term « terpene » to avoid confusion. The name « terpene » is a shortened form of « terpentine », an obsolete spelling of « turpentine ».
Terpenoids (or isoprenoids), while sometimes used interchangeably with « terpenes », are modified terpenes, containing functional groups, usually oxygenated. Some use the terms terpenes and terpenoids interchangeably. Both have strong and often pleasant odors that can protect their hosts or attract pollinators. The inventory of terpenes and terpenoids is estimated at 55,000 chemical units.
The Nobel Prize in Chemistry was awarded to Leopold Ružička in 1939 « for his work on polymethylenes and higher terpenes », « including the first chemical synthesis of the male sex hormones ».