Quantitative structure-activity bulk parameters

The two major approaches currently in use and under discussion [50,57,58] for the prediction of Kqc of neutral compounds are KOCWIN, which is part of the EpiSuite package [39], and different pp-LEER equations [48,50,58]. KOCWIN is a quantitative structure-activity relationship (QSARs) developed with molecular connectivity indices (MCI) [59]. pp-LEERs describe partitioning based on a few fundamental solute-bulk phase intermolecular interactions such as van-der-Waals interactions and H-bonding. The partitioning behavior of a given solute can thus be represented by a small set of descriptors (Abraham solvation parameters), which indicate its capacity for a set of defined intermolecular interactions. 

Charton, M., and B.I. Charton Significance of Volume and Bulk Parameters in Quantitative Structure-Activity Relationships. J. Org. Chem. 44,2284-2288 (1979). 

Another classical measure of the molecular geometry of substituents is the Verloop steric parameter. This is calculated from bond angles and atomic dimensions— primarily the lengths of substituent groups and several measures of their width. Trivial as this may sound, the consideration of molecular bulk is an important and often neglected factor in making multiple quantitative correlations of structure and pharmacological activity. Balaban et al. (1980) devised several related methods that are still in use today. 

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