Limonene is a colourless liquid hydrocarbon and is the major component in the oil of citrus fruit peels. It is a chiral molecule, and biological sources produce one enantiomer. The principal industrial source, citrus fruit, contains D-limonene, which is the (R)-enantiomer. Racemic limonene is known as dipentene.
The D-isomer occurs more commonly in nature as the fragrance of oranges and is used as a flavouring agent in food manufacturing.