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Terpenes

Terpenes are widespread in nature, mainly in plants as constituents of essential oils. Many terpenes are hydrocarbons, but oxygen-containing compounds such as alcohols, aldehydes or ketones (terpenoids) are also found. Their building block is the hydrocarbon isoprene, CH2=C(CH3)-CH=CH2 (isoprene rule, Wallach 1887). Terpene hydrocarbons therefore have molecular formulas (C5H8)n, they are classified according to the number of isoprene units: 
                  number of isoprene units
monoterpenes      2
sesquiterpenes    3
diterpenes        4
triterpenes       6
tetraterpenes     8
Examples of monoterpenes are: pinene, nerol, citral, camphor, menthol, limonene. Examples of sesquiterpenes are: nerolidol, farnesol. Examples of diterpenes are: phytol, vitamin A1. Squalene is an example of a triterpene, and carotene (provitamin A1) is a tetraterpene.

Scheme: Formulas of several terpenes

Terpene

Burkhard Kirste, 1994-08-19, 1998-02-02

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