A linear free energy analysis of the surface tension of organic liquids

The surface tensions (gamma(2)) of organic liquids have been shown to correlate with empirical solute parameters by the linear free energy relationship (LSER): gamma(2) = 14.8 + 11.4 R-2 + 10.6 pi(2) + 3.4 (Sigma alpha(2) x Sigma beta(2))(1/2) + 2.95 V-X + 0.87 N-C where R-2, pi(2), Sigma alpha(2), Sigma beta(2), and V-X are medium-insensitive solute parameters representing, respectively, the excess molar refraction, dipolarity, the hydrogen bond acidity and basicity, and the molar volume of the organic liquid. The term N-C, which is specific to the n-alkanes, is a function of the total number of carbon atoms in the n-alkane. The free energy contribution from intermolecular hydrogen bond formation is modeled by using the geometric mean parameter (Sigma alpha(2) x Sigma beta(2))(1/2). This new LSER provides a useful conceptual framework for understanding the interaction of surface molecules with the underlying molecules of the bulk liquid, as well as permitting estimation of surface tension directly from molecular structure.