Monoterpenes are a class of terpenes that consist of two isoprene units and have the molecular formula C10H16. Monoterpenes may be linear (acyclic) or contain rings. Biochemical modifications such as oxidation or rearrangement produce the related monoterpenoids.
1 Acyclic monoterpenes 2 Monocyclic monoterpenes 3 Bicyclic monoterpenes 4 Role in climate 5 Uses 6 See also 7 References
Acyclic monoterpenes Biosynthetically, isopentenyl pyrophosphate and dimethylallyl pyrophosphate are combined to form geranyl pyrophosphate.
Myrcene, a monoterpene
Elimination of the pyrophosphate group leads to the formation of acyclic monoterpenes such as ocimene and the myrcenes. Hydrolysis of the phosphate groups leads to the prototypical acyclic monoterpenoid geraniol. Additional rearrangements and oxidations provide compounds such as citral, citronellal, citronellol, linalool, and many others. Many monoterpenes found in marine organisms are halogenated, such as halomon. Monocyclic monoterpenes In addition to linear attachments, the isoprene units can make connections to form rings. The most common ring size in monoterpenes is a six-membered ring. A classic example is the cyclization of geranyl pyrophosphate to form limonene.
The terpinenes, phellandrenes, and terpinolene are formed similarly.
Other bicyclic monoterpenes include carene, sabinene, camphene, and thujene. Camphor, borneol and eucalyptol are examples of bicyclic monoterpenoids containing ketone, alcohol, and ether functional groups, respectively. Role in climate Monoterpenes are emitted by forests and form aerosols that can serve as cloud condensation nuclei (CCN). Such aerosols can increase the brightness of clouds and cool the climate. Uses Several monoterpenes derivatives have antibacterial activity, such as linalool. See also
Diterpene Iridoid Sesquiterpene Triterpene
^ D. V. Spracklen; B. Bonn; K. S. Carslaw (2008). "Boreal forests, aerosols and the impacts on clouds and climate" (PDF). Philosophical Transactions of the Royal Society A. 366 (1885): 4613–26. Bibcode:2008RSPTA.366.4613S. doi:10.1098/rsta.2008.0201. PMID 18826917.
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Types of Terpenes and Terpenoids (# of isoprene units)
Acyclic (linear, cis and trans forms)
Monocyclic (single ring)
Bicyclic (2 rings)
Iridoids (cyclopentane ring)
Limonene Terpinene Phellandrene Umbellulone
Linalool Citronellal Citral Citronellol Geraniol Geranyl pyrophosphate
Grapefruit mercaptan menthol p-Cymene thymol Perillyl alcohol Carvacrol
Camphor Borneol Eucalyptol Halomon Eucalyptol Pinene Ascaridole
Farnesyl pyrophosphate Artemisinin Bisabolol
Geranylgeranyl pyrophosphate Gibberellin Retinol Retinal Phytol Taxol Forskolin Aphidicolin Salvinorin A
Campesterol beta Sitosterol gamma sitosterol Stigmasterol
Saponins Squalane Lanosterol Acids
Oleanolic acid Ursolic acid Betulinic acid Moronic acid
Tetraterpenoids (Carotenoids) (8)
Alpha-Carotene Beta-Carotene Gamma-Carotene Delta-Carotene Lycopene Neurosporene Phytofluene Phytoene
Canthaxanthin Cryptoxanthin Zeaxanthin Astaxanthin Lutein Rubixanthin
sap, resins, latex of many plants, e.g. rubber
Activated isoprene forms