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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.

Contents

1 Acyclic monoterpenes 2 Monocyclic monoterpenes 3 Bicyclic monoterpenes 4 Role in climate 5 Uses 6 See also 7 References

Acyclic monoterpenes[edit] Biosynthetically, isopentenyl pyrophosphate and dimethylallyl pyrophosphate are combined to form geranyl pyrophosphate.

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[edit] 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. Hydroxylation
Hydroxylation
of any of these compounds followed by dehydration can lead to the aromatic p-cymene. Important terpenoids derived from monocyclic terpenes are menthol, thymol, carvacrol and many others. Bicyclic monoterpenes[edit] Geranyl pyrophosphate
Geranyl pyrophosphate
can also undergo two sequential cyclization reactions to form bicyclic monoterpenes, such as pinene which is the primary constituent of pine resin.

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[edit] 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.[1] Uses[edit] Several monoterpenes derivatives have antibacterial activity, such as linalool. See also[edit]

Diterpene Iridoid Sesquiterpene Triterpene

References[edit]

^ 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. 

v t e

Types of Terpenes and Terpenoids (# of isoprene units)

Basic forms:

Acyclic (linear, cis and trans forms) Monocyclic (single ring) Bicyclic (2 rings) Iridoids (cyclopentane ring) Iridoid
Iridoid
glycosides (iridoids bound to a sugar) Steroids (4 rings)

Hemiterpenoids (1)

Isoprene
Isoprene
(C5H8) Prenol Isovaleric acid

Monoterpene
Monoterpene
(C10H16)(2)

Acyclic

Ocimene Myrcenes

Monocyclic

Limonene Terpinene Phellandrene Umbellulone

Bicyclic

Pinene
Pinene
(β and α Camphene Thujene Sabinene Carene

Monoterpenoids (2,modified)

Acyclic

Linalool Citronellal Citral Citronellol Geraniol Geranyl pyrophosphate

Monocyclic

Grapefruit mercaptan menthol p-Cymene thymol Perillyl alcohol Carvacrol

Bicyclic

Camphor Borneol Eucalyptol Halomon Eucalyptol Pinene Ascaridole

Sesquiterpenoids
Sesquiterpenoids
(3)

Farnesyl pyrophosphate Artemisinin Bisabolol

Diterpenoids (4)

Geranylgeranyl pyrophosphate Gibberellin Retinol Retinal Phytol Taxol Forskolin Aphidicolin Salvinorin A

Sesterterpenoids (5)

geranylfarnesol

Triterpenoids (6)

Steroids

Phytosterols

Campesterol beta Sitosterol gamma sitosterol Stigmasterol

Tocopherols Cholesterol Testosterone Cholecalciferol
Cholecalciferol
(Vit D) Ecdysones

Other

Saponins Squalane Lanosterol Acids

Oleanolic acid Ursolic acid Betulinic acid Moronic acid

Sesquarterpenes/oids (7)

ferrugicadiol tetraprenylcurcumene

Tetraterpenoids (Carotenoids) (8)

Carotenes

Alpha-Carotene Beta-Carotene Gamma-Carotene Delta-Carotene Lycopene Neurosporene Phytofluene Phytoene

Xanthophylls:

Canthaxanthin Cryptoxanthin Zeaxanthin Astaxanthin Lutein Rubixanthin

Polyterpenoids (many)

sap, resins, latex of many plants, e.g. rubber

Norisoprenoids (modified)

3-oxo-α-ionol 7,8-dihydroionone

Synthesis

Terpene
Terpene
synthase enzymes (many), having in common a Terpene
Terpene
synthase N terminal domain (protein domain)

Activated isoprene forms

Isopentenyl pyrophosphate
Isopentenyl pyrophosphate
(IPP) Dimethylallyl pyr

.