The correlation of chemical structure and odor has been a puzzling problem for chemists as well as perfumers since the emergence of synthetic aromatic chemicals for over 100 years. Several theories have been proposed to model the interaction between an odorous chemical substance and a receptor expected to be directly at the nerve ends in the regio olfactoria.
One generally accepted explanation assumes a correlation between a basic shape of the molecule and its prevalent odor character in analogy to the classical key-lock interaction between an active agent and its receptor site. This does not interfere with theories which assume that the same molecule may bind to several receptor sites, thereby generating a varied i.e. “mixed" response to explain the seemingly endless multitude of olfactorial perceptions.
All of the current theories lack a biochemical foundation and knowledge of the true geometry of the receptor site in the olfactory bulbus. This and a still unexplained fact that not only diverse chemical structures but also analogues of a similar basic structure sometimes smell quite differently is one of tbe reasons we still need more information about the correlations between different chemical structures and their odor perceptions.