Partition coefficients of 5-(substituted benzyl)-2,4-diaminopyrimidines.

: The pK-values of 19 and the partition coefficients P of 79 5-benzyl-2,4-diaminopyrimidines substituted in the benzene moiety were experimentally determined. The results of a multiple regression analysis show that the partition coefficients cannot be calculated with reasonable accuracy starting from fragmental constants. Interactions between substituents can reduce P-values by an order of magnitude below those obtained by applying Hansch's and Rekker's models. Interaction terms between different substituents were calculated. Similar effects are to be expected for other poly-substituted aromatic compounds.