"Although deuteration does not appreciably change molecular shape, atom size, or bond length or stiffness, it doubles hydrogen mass, thus affecting the overall vibrational modes of an odorant. Therefore, if recognition of molecular shape alone was the sole determinant for odor character (2, 3), then flies should not respond differentially to deuterated [d, where d(x) denotes replacement of x nonexchangeable hydrogens with deuterium atoms] and nondeuterated/normal (i.e., H-) odorants. To address this hypothesis, we took advantage of the commercial availability of acetophenone (ACP) carrying three, five, or eight deuterium atoms (d3, d5, and d8) in place of the respective hydrogens in the normal molecule (h-ACP). Equal amounts (75 μL) of each odorant were diluted to 1 mL in isopropyl myristate and we quantified (Fig. 1A) the response of groups of flies to each odorant versus unscented air traversing the arms of a standard T-maze (Materials and Methods) (19, 20). When given a choice between normal ACP (i.e., h-ACP) and air, the excess flies present in the odor-delivering maze arm indicated that, at the dilution used, the odorant was attractive. However, replacing only three hydrogen atoms with deuterium eliminated this spontaneous preference as the flies distributed nearly equally in the arms of the maze. The d5-ACP was mildly aversive and the fully substituted d8-ACP was the most aversive of the four isotopes."

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3048096/