Phellandrene is the name for 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.
alpha-Phellandrene was named after Eucalyptus phellandra, now called Eucalyptus radiata, from which it can be isolated. It is also a constituent of the essential oil of Eucalyptus dives. beta-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 alpha phellandrene isomer can form hazardous and explosive peroxides on contact with air at elevated temperature.