Testing the Vibrational Theory of Olfaction: A Bio-organic Chemistry Laboratory Experiment Using Hooke’s Law and Chirality

Abstract

Sense of smell is one of the important senses that enables us to interact with our environment. The molecular basis of olfactory signal transduction is a fascinating area for organic chemistry educators to explore in terms of developing undergraduate laboratory activities at the interface of chemistry and biology. In this paper, a guided-inquiry laboratory experiment is described to test the vibrational theory of olfaction according to which a molecule’s vibrations determine its odor. Two key predictions of this theory were tested in this experiment. The first was that deuterated odorants and their nondeuterated counterparts would have different odors. This is because application of Hooke’s law leads one to predict that the frequency of a C–H bond vibration is different compared to a C–D bond vibration. The second key prediction that students tested was that enantiomeric odorants should have the same odor since their individual bond vibrations should be identical. Contrary to these predictions, students observed that the enantiomeric odorants had different odors whereas deuterated acetophenone and its nondeuterated counterpart had the same odor. Therefore, students concluded that their empirical evidence does not support the vibrational theory of olfaction. A postlab evaluation showed student comprehension of the principles underlying the olfaction laboratory experiment.