The continuing debate over the basis of odorant recognition with respect to the molecular shape ("lock and key") theory versus the vibrational theory could potentially be resolved by the testing of (13)C-labeled odorants. The application of (13)C isotopomers is discussed herein by means of DFT-calculated IR vibrations and Gibbs' free energies (ΔG) for acetophenone and octan-1-ol, two odorants for which the (2)D (deuterium) isotopomers have previously been shown to be discernible from their respective (1)H (normal) counterparts by Drosophila melanogaster.