Explorations of molecular structure-property relationships

The problem of the relationship between the structure of a molecule and its physical, chemical, and biological properties is one of the most fundament al in chemistry. Three molecular structure-properly studies are discussed a s illustrations of different approaches to this problem. In the first study the carcinogenic activities of polycyclic aromatic hydrocarbons and their derivatives are examined. Molecular orbital calculations of the presumptive activation steps and species for these compounds (based on the "bay region " theory of activation) are seen to yield a surprisingly good guide to the observed carcinogenic activities. Both activation and deactivation steps ar e considered. The second study reviews structure-properly work on the tissu e solubilities of halogenated hydrocarbons. Relatively simple structural de scriptors give a good account of the solubilities of these compounds in blo od, muscle, fat, and liver tissue. With the aid of principal components ana lysis it is shown that there are two dominant dimensions to this problem, w hich can be interpreted in terms of solubilities of the compounds in lipid and saline environments. The final study, which examines the boiling points of aliphatic alcohols, illustrates the value of using more than one descri ptor set. The (perhaps surprising) conclusion is that a theoretical model c an sometimes be more accurate than the data upon which it is based. Moreove r, two models are better than one.