Molecular descriptors, group additive

Group Additive Molecular Descriptors Log P values were... 

The derivation of the topological distance matrix from the molecular graph is followed by the assignment of PPPs to the nodes of the graph. The following list provides chemical definitions of the five PPP types that are implemented in the CATS descriptor. The upper-case letter in parentheses is the abbreviation of each PPP type. Additionally, a functional group description is paired with its corresponding SMARTS in square brackets ... 

The negative signs are physically reasonable because these additional parameters would be expected to be associated with increased intramolecular attractions. The authors provided no measure of intercorrelation indeed, one might expect some correlation of a, the average molecular polarizability, with the presence of C=0, COOH, NO2, and CN groups. The counting descriptors are not QM quantities their inclusion is not philosophically satisfying, but they do improve the fit. 

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