γ-terpinene
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The terpinenes are a group of
isomer In chemistry, isomers are molecules or polyatomic ions with identical molecular formula – that is, the same number of atoms of each element (chemistry), element – but distinct arrangements of atoms in space. ''Isomerism'' refers to the exi ...
ic hydrocarbons that are classified as
monoterpene 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 (monocyclic and bicyclic). Modified terpenes, such as those containing oxygen func ...
s. They each have the same molecular formula and carbon framework, but they differ in the position of carbon-carbon double bonds. α-Terpinene has been isolated from
cardamom Cardamom (), sometimes cardamon or cardamum, is a spice made from the seeds of several plants in the genus (biology), genera ''Elettaria'' and ''Amomum'' in the family Zingiberaceae. Both genera are native to the Indian subcontinent and Indon ...
and
marjoram Marjoram (, ''Origanum majorana'') is a cold-sensitive perennial plant, perennial herb or undershrub with sweet pine and citrus flavours. In some Middle Eastern countries, marjoram is synonymous with oregano, and there the names sweet marjoram ...
oils, and from other natural sources. β-Terpinene has no known natural source but has been prepared from
sabinene Sabinene is a natural bicyclic monoterpene with the molecular formula C10H16. It is isolated from the essential oils of a variety of plants including Marjoram, holm oak (''Quercus ilex'') and Norway spruce (''Picea abies''). It has a strained ...
. γ-Terpinene and δ-terpinene (also known as terpinolene) have been isolated from a variety of plant sources. They are all colorless liquids with a turpentine-like odor.


Production and uses

α-Terpinene is produced industrially by acid-catalyzed rearrangement of α-
pinene Pinene is a collection of unsaturated bicyclic monoterpenes. Two geometric isomers of pinene are found in nature, α-pinene and β-pinene. Both are chiral. As the name suggests, pinenes are found in pines. Specifically, pinene is the major comp ...
. It has perfume and flavoring properties but is mainly used to confer pleasant odor to industrial fluids. Hydrogenation gives the saturated derivative ''p''-menthane.


Biosynthesis of α-terpinene

The biosynthesis of α-terpinene and other terpenoids starts with the isomerization of
geranyl pyrophosphate Geranyl pyrophosphate (GPP), also known as geranyl diphosphate (GDP), is the pyrophosphate ester of the terpenoid geraniol. Its salts are colorless. It is a precursor to many thousands of natural product, natural products. Occurrence GPP is an int ...
to linalyl pyrophosphate (LPP). LPP then forms a resonance-stabilized cation by loss of the pyrophosphate group. Cyclization is then completed thanks to this more favorable stereochemistry of the LPP cation, yielding a terpinyl cation. Finally, a 1,2-hydride shift via a Wagner-Meerwein rearrangement produces the terpinen-4-yl cation. It is the loss of a hydrogen from this cation that generates α-terpinene.


Plants that produce terpinene

* ''
Cuminum cyminum Cumin (, ; ; ''Cuminum cyminum'') is a flowering plant in the family Apiaceae, native to the Irano-Turanian Region. Its seeds – each one contained within a fruit, which is dried – are used in the cuisines of many cultures in both whole ...
'' * '' Melaleuca alternifolia'' * ''
Cannabis ''Cannabis'' () is a genus of flowering plants in the family Cannabaceae that is widely accepted as being indigenous to and originating from the continent of Asia. However, the number of species is disputed, with as many as three species be ...
'' * '' Origanum syriacum'' *'' Coriandrum sativum'' * ''
Monarda fistulosa ''Monarda fistulosa'', the wild bergamot or bee balm,Wild Bergamot
, Edmonton Naturalization Group ...
''


References

{{Reflist Monoterpenes Dienes Cyclohexenes Cyclohexadienes