Terpene

Terpenes (/ˈtɜːrpiːn/) are a large and diverse class of natural products with the general formula (C₅H₈)_n, where n ≥ 2. They serve as crucial biosynthetic building blocks in many organisms, particularly plants. Comprising more than 30,000 compounds, these unsaturated hydrocarbons are produced predominantly by plants, particularly conifers. In plants, terpenes and terpenoids are important mediators of ecological interactions, while some insects use some terpenes as a form of defense. Other functions of terpenoids include cell growth modulation and plant elongation, light harvesting and photoprotection, and membrane permeability and fluidity control.

Terpenes are classified by the number of carbons: monoterpenes (C₁₀), sesquiterpenes (C₁₅), diterpenes (C₂₀), as examples. The terpene alpha-pinene is a major component of turpentine, a common solvent.

One terpene that has major applications is natural rubber (i.e., polyisoprene). The possibility that other terpenes could be used as precursors to produce synthetic polymers has been investigated. Many terpenes have been shown to have pharmacological effects. Terpenes are also components of some traditional medicines, such as aromatherapy, and as active ingredients of pesticides in agriculture.

The term Terpen (German) was coined in 1866 by the German chemist August Kekulé to denote all hydrocarbons having the empirical formula C₁₀H₁₆, of which camphene was one. Previously, many hydrocarbons having the empirical formula C₁₀H₁₆ had been called "camphene", but many other hydrocarbons of the same composition had different names. Kekulé coined the term "Terpen" in order to reduce the confusion. The name is a shortened form of "Terpentin", the german word for "turpentine".

Although sometimes used interchangeably with "terpenes", terpenoids (or isoprenoids) are modified terpenes that contain additional functional groups, usually oxygen-containing. The terms terpenes and terpenoids are often used interchangeably, however. Furthermore, terpenes are produced from terpenoids and many terpenoids are produced from terpenes. Both have strong and often pleasant odors, which may protect their hosts or attract pollinators. The number of terpenes and terpenoids is estimated at 55,000 chemical entities.

The 1939 Nobel Prize in Chemistry was awarded to Leopold Ružička "for his work on polymethylenes and higher terpenes", "including the first chemical synthesis of male sex hormones."

Terpenes are major biosynthetic building blocks. Steroids, for example, are derivatives of the triterpene squalene. Terpenes and terpenoids are also the primary constituents of the essential oils of many types of plants and flowers. In plants, terpenes and terpenoids are important mediators of ecological interactions. For example, they play a role in plant defense against herbivory, disease resistance, attraction of mutualists such as pollinators, as well as potentially plant-plant communication. They appear to play roles as antifeedants. Other functions of terpenoids include cell growth modulation and plant elongation, light harvesting and photoprotection, and membrane permeability and fluidity control.

Higher amounts of terpenes are released by trees in warmer weather, where they may function as a natural mechanism of cloud seeding. The clouds reflect sunlight, allowing the forest temperature to regulate.