IUPAC names
α: 2-Methyl-5-(1-methylethyl)-1,3-cyclohexadiene
β: 3-Methylene-6-(1-methylethyl)cyclohexene
3D model (JSmol)
ECHA InfoCard 100.014.121 Edit this at Wikidata
EC Number
  • (α): 202-792-5
  • (β): 209-081-9
  • (−)-(α): 224-167-6
Molar mass 136.24 g/mol
Appearance Colorless oil (α and β)
Density α: 0.846 g/cm3
β: 0.85 g/cm3
Boiling point α: 171-172 °C
β: 171-172 °C
Insoluble (α and β)
GHS pictograms GHS02: FlammableGHS08: Health hazard
GHS Signal word Danger
H226, H304
P210, P233, P240, P241, P242, P243, P280, P301+310, P303+361+353, P331, P370+378, P403+235, P405, P501
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

Phellandrenes are a pair of organic compounds that have a similar molecular structure and similar chemical properties. α-Phellandrene and β-phellandrene are cyclic monoterpenes and are double-bond isomers. In α-phellandrene, both double bonds are endocyclic and in β-phellandrene, one of them is exocyclic. Both are insoluble in water, but miscible with ether.

α-Phellandrene was named after Eucalyptus phellandra, now called Eucalyptus radiata, from which it can be isolated.[2] It is also a constituent of the essential oil of Eucalyptus dives.[3] β-Phellandrene has been isolated from the oil of water fennel and Canada balsam oil.

The phellandrenes are used in fragrances because of their pleasing aromas. The odor of β-phellandrene has been described as peppery-minty and slightly citrusy.

The α-phellandrene isomer can form hazardous and explosive peroxides on contact with air at elevated temperatures.[4]


The biosynthesis of phellandrene begins with dimethylallyl pyrophosphate and isopentenyl pyrophosphate condensing in an SN1 reaction to form geranyl pyrophosphate. The resultant monoterpene undergoes cyclization to form a menthyl cationic species. A hydride shift then forms an allylic carbocation. Finally, an elimination reaction occurs at one of two positions, yielding either α-phellandrene or β-phellandrene.[5]


  1. ^ The Merck Index, 12th Edition, 7340, 7341
  2. ^ Jacobs, S.W.L., Pickard, J., Plants of New South Wales, 1981, ISBN 0-7240-1978-2.
  3. ^ Boland, D.J., Brophy, J.J., and A.P.N. House, Eucalyptus Leaf Oils, 1991, ISBN 0-909605-69-6.
  4. ^ Urben, Peter (2007). Bretherick's Handobook of Reactive Chemical Hazards. 1 (7 ed.). Butterworth-Heinemann. p. 1154.
  5. ^ Dewick, Paul M. Medicinal natural products : a biosynthetic approach (3rd ed.). Chichester, West Sussex, United Kingdom. ISBN 9780470741689. OCLC 259265604.