Figure 1.

Molecular structures of the enantiomers of limonene, α-pinene, and carvone. The enantiomers have distinct odor characteristics (quality and threshold), which are attributed to the enantiomeric configuration. R-(−)-Carvone is the main consitutent in spearmint essential oil, and S-(+)-carvone is the main constituent in the essential oil of carraway and dill. R-(+)-Limonene is the main constituent of the volatile oils expressed from the fresh peel of Citrus spp. fruits. S-(−)-limonene is present in the oil of fir and the needles and young twigs of Abies alba (Pinaceae).