The Odors of Optical Isomers

Scent through the Looking Glass

“…The individual enantiomers had been prepared by Werner and Conrad [16], and they reported that the dextrorotatory diester was almost odorless whereas the laevorotatory enantiomer possessed a strong odor. Over fifty years later, Posvic [9] re-investigated this work, and made an interesting discovery. Werner and Conrad had prepared the isomers from phthalic acid as shown in Scheme 2.…”

“…This was particularly so when starting from different feedstocks and especially those of natural origin. He, therefore, designed a synthesis of all stereoisomers of 3,5-dimethylcyclohexanone starting from a common achiral precursor, m-xylenol, i.e., 3,5-dimethylphenol (9) [3] [4] (Scheme 1).…”

“…In this carefully thought out experiment, von Braun and co-workers started by hydrogenating 3,5-dimethylphenol (9), and then oxidised the resultant cyclohexanol 10 to the ketone 11. Oximation of ketone 11 allowed them to separate the meso-isomer 12 from the pair of enantiomers 13 and 14.…”

“…This emotional element tended to cloud evaluation of facts, and it took a cool mind to retain objectivity. One such example was Posvic [9] who, having demonstrated (vide infra) that one particular pair of enantiomers possessed identical odors, reminded readers of his paper that this did not constitute a proof of the vibrational theory.…”