HYDROGEN-BONDING .35. RELATIONSHIP BETWEEN HIGH-PERFORMANCE LIQUID-CHROMATOGRAPHY CAPACITY FACTORS AND WATER-OCTANOL PARTITION-COEFFICIENTS

The solvation equation log SP = c + rR(2) + s pi(2)(H) + a Sigma alpha(2)(H) + b Sigma beta(2)(H) + nu V-x has been applied to reversed-phase HPLC capacity factors, as log k', for solutes on a C-18 bonded phase, with various water-methanol mobile phases, using data by Yamagami and Takao. Here, SP is a property for a series of solutes in a fixed solvent system, and the explanatory variables are solute descriptors as follows: R(2) is an excess molar refraction, pi(2)(H) is the solute dipolarity/polarizability, Sigma alpha(2)(H) and Sigma beta(2)(H) are the solute overall or effective hydrogen-bond acidity and basicity, and V-x, is the McGowan characteristic volume; c, r, s, a, b and nu are constants. It is shown that the blend of factors that influence log k' in any given system is not the same as that which influences log P-oct. In particular, solute hydrogen-bond acidity considerably influences log k', but has no effect on log P-oct. It follows that when log k' values are used to estimate log P-oct, great care has to be taken to match the training set of solutes in the correlation equation, with the solutes for which log P-oct is to be determined.