Terpenes are a class of unsaturated aliphatic hydrocarbons distinguished by at least one branched 5-carbon ring structure (an isoprene unit). Additional isoprene units and other organic functional groups may be attached. Terpenes are insoluble in water, but dissolve in alcohol. The lighter terpenes are volatile and aromatic. These are derived from plants, or are synthesized from isoprene, and are a component of essential oils. Steroids and xanthophylls are larger molecules that contain terpene structures.

A few terpenes with which you might already be familiar:
• menthol, an alcohol present in peppermint oil
• limonene, an aldehyde in lemon oil
• nerol, derived from orange blossoms
• nepetalactone, present in catnip
• zingiberene, an aldehyde from ginger
• thujone, present in aniseed oil
• turpentine, a solvent
• camphor

Sources consulted:
An article on toxicity, www.emedicine.com/emerg/topic572.htm
Article on the structure and chemistry of terpenes, www.contentotrade.com/Terpene/eng/Chimica%20del%20Terpene.htm
General information regarding the class of terpenes, www.chemie.fu-berlin.de/chemistry/oc/terpene/terpene_en.html
An article on biosynthesis of terpenes, sbl.salk.edu/noel/terpenoid_natural_products.html and www.biologie.uni-hamburg.de/b-online/e20/20b.htm

Ter"pene (?), n. [See Turpentine.] Chem.

Any one of a series of isomeric hydrocarbons of pleasant aromatic odor, occurring especially in coniferous plants and represented by oil of turpentine, but including also certain hydrocarbons found in some essential oils.

 

© Webster 1913.