DEPENDENCE OF ODOR INTENSITY ON THE HYDROPHOBIC PROPERTIES OF MOLECULES - QUANTITATIVE STRUCTURE ODOR INTENSITY RELATIONSHIP

The relationship between odor intensity and physicochemical properties of odorants was investigated using the Hansch approach, a quantitative structure-activity relationship technique which utilizes linear free energy relationship (LFER) parameters and multiple regression analysis. Literature odor threshold and suprathreshold data for homologous series of compounds whose members had noncolinear hydrophobic, steric, and polar parameters were successfully correlated only with the hydrophobicity parameter log P, the log [1-octanol/water partition coefficient]. Poor correlations were achieved with steric and polar parameters. This indicated that odor intensity depended upon the hydrophobic and not the odorant's steric or polar properties. Log P also correlated well with odor intensity data for a wide variety of odorants of different functionality. Addition of a hydrogen-bonding indicator parameter, HB, to equations relating odor intensity for nonhomologous series significantly improved the correlations. The successful correlations with the hydrophobicity term, log P, indicates that the ability of an odorant to partition from the medium in which it is dissolved into the atmosphere and its ability to partition through mucus and membrane layers to reach olfactory receptor sites are the important factors in determining odor intensity. © 1979, American Chemical Society. All rights reserved.