Question

1. Carvone exists as a pair of enantiomers(see structure p 23). (R)-(-)-carvone smells like spearment, whereas (S)-(+)-carvone smells like caraway. Why do these enantiomers have different smells (i.e., different biological activity) ?

2. Why must enantiomers be converted to diastereomers before separation processes such as crystallization ?

Answer 1

1. The strong dipoles (c=o bond in carvone) show polarization effects. In mint carvone, the c=o is not detected because it is wrongly oriented. Adding back the carbonyl vibration by smelling simultaneously a small carbonyl bearing odorant (e.g acetone,butanone) with mint carvone would change the smell from mint to caraway.

2. Usually enantiomers are separated preceding conversion of enantiomers to diastereomers because of their practical identical chemical and physical properties entantiomers cannot be separated directly