Carvone

Carvone is a member of a family of chemicals called terpenoids. Carvone is found naturally in many essential oils, but is most abundant in the oils from seeds of caraway (Carum carvi), spearmint (Mentha spicata), and dill.

Stereoisomerism and odor

Carvone forms two mirror image forms or enantiomers: R-(–)-carvone smells like spearmint leaves. Its mirror image, S-(+)-carvone, smells like caraway seeds. The fact that the two enantiomers are perceived as smelling different is evidence that olfactory receptors must contain chiral groups, allowing them to respond more strongly to one enantiomer than to the other. Not all enantiomers have distinguishable odors. Squirrel monkeys have also been found to be able to discriminate between carvone enantiomers.

The two forms are also referred to by the older names of laevo (L) referring to R-(–)-carvone, and dextro (D) referring to S-(+)-carvone.

Occurrence

S-(+)-Carvone is the principal constituent (60-70%) of the oil from caraway seeds (Carum carvi), which is produced on a scale of about 10 tonnes per year. It also occurs to the extent of about 40-60% in dill seed oil (from Anethum graveolens), and also in mandarin orange peel oil. R-(–)-Carvone is also the most abundant compound in the essential oil from several species of mint, particularly spearmint oil (Mentha spicata), which is composed of 50-80% R-(–)-carvone. Spearmint is a major source of naturally produced R-(–)-carvone. However, the majority of R-(–)-carvone used in commercial applications is synthesized from R-(+)-limonene. The R-(–)-carvone isomer also occurs in kuromoji oil. Some oils, like gingergrass oil, contain a mixture of both enantiomers. Many other natural oils, for example peppermint oil, contain trace quantities of carvones.