imonene, a compound synthesized by plants, is sequestered by butterflies of the genus Papilio (the swallowtails) and used as a defensive substance. Explain the difference in the two limonene molecules shown below, why would they have different scents? -limonene (lemon scent) (R)- limonene orange scent) Solution (S)-limonene and (R)-limonene are two different compounds known as enantiomers which are mirror images of each other. Enantiomers are two different compounds which have different biological activity. Enantiomers differ in the arrangement of the groups around the chiral center which means the spatial arrangement of the groups around the chiral center is different in each enantiomer and thus they display different biological activity. This difference in biological ctivity arises due to the binding of the active sites (functional group) present in the molecule with the chiral receptors. The binding of one enatiomer to the chiral receptors is different from the other enantiomer and hence they have different biological activity. Due to the same reason, (S)- limonene has lemon scent while (R)-limonene has orange sent..