Α-terpinene

Terpinenes

α-Terpinene β-Terpinene
γ-Terpinene δ-Terpinene (terpinolene)
Names
IUPAC names α: 4-Methyl-1-(1-methylethyl)-1,3-cyclohexadiene β: 4-Methylene-1-(1-methylethyl)cyclohexene γ: 4-Methyl-1-(1-methylethyl)-1,4-cyclohexadiene δ: 1-Methyl-4-(propan-2-ylidene)cyclohex-1-ene
Identifiers
CAS Number	99-86-5 (α) Y 99-84-3 (β) Y 99-85-4 (γ) Y 586-62-9 (δ) Y
3D model (Jmol)	(α): Interactive image (β): Interactive image (γ): Interactive image (δ): Interactive image
ChEBI	CHEBI:59159 Y
ChemSpider	60205 Y
ECHA InfoCard	100.029.440
InChI InChI=1S/C10H16/c1-8(2)10-6-4-9(3)5-7-10/h6,8H,3-5,7H2,1-2H3 Y Key: SCWPFSIZUZUCCE-UHFFFAOYSA-N Y
SMILES (α): CC1=CC=C(C(C)C)CC1 (β): C=C1CC=C(C(C)C)CC1 (γ): CC1=CCC(C(C)C)=CC1 (δ): C/C(C)=C1CCC(C)=CC/1
Properties
Chemical formula	C10H16
Molar mass	136.24 g·mol−1
Density	α: 0.8375 g/cm3 β: 0.838 g/cm3 γ: 0.853 g/cm3
Melting point	α: 60-61 °C
Boiling point	α: 173.5-174.8 °C β: 173-174 °C γ: 183 °C
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
Y  (what is YN ?)
Infobox references

The terpinenes are a group of isomeric hydrocarbons that are classified as terpenes. 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 and marjoram oils, and from other natural sources. β-Terpinene has no known natural source, but has been prepared synthetically from sabinene. γ-Terpinene and δ-terpinene (also known as terpinolene) are natural and have been isolated from a variety of plant sources.

α-Terpinene is a perfume and flavoring chemical used in the cosmetics and food industries. Its use in both the pharmaceutical and the electronics semi-conductor manufacturing industries has also proven to be valuable.

The biosynthesis of α-terpinene and other terpenoids occurs via the mevalonate pathway because its starting reactant, dimethylallyl pyrophosphate (DMAPP), is derived from mevalonic acid.

Geranyl pyrophosphate (GPP) is produced from the reaction of a resonance-stable allylic cation, formed from the loss of the pyrophosphate group from DMAPP, and isopentenyl pyrophosphate (IPP), and the subsequent loss of a proton. GPP then loses the pyrophosphate group to form the resonance-stable geranyl cation. The reintroduction of the pyrophosphate group to the cation produces GPP isomer, known as linalyl pyrophosphate (LPP). LPP then forms a resonance-stable cation by losing its pyrophosphate group. Cyclization is then completed thanks to this more favorable stereochemistry of the LPP cation, now 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.