Linear solvation energy relationships. A comparison of molar volume and intrinsic molecular volume as measures of the cavity term in reversed phase liquid chromatography

Reversed-phase liquid chromatographic capacity factors are well correlated by an equation of the form: {Mathematical expression} where mV/100 measures the cavity term and π^*, β, and α are the solvatochromic parameters that measure solute dipolarity/polarizability, hydrogen bond acceptor basicity, and hydrogen bond donor acidity respectively. Liquid molar volume (molecular weight divided by liquid density at 20°C) {Mathematical expression}, and computer-calculated intrinsic (van der Waals) molecular volume, {Mathematical expression}, are compared as measures of the cavity term in a number of correlations. {Mathematical expression} leads to more precise correlations as well as to a "cleaner" dissection of the multiple solute/solvent interactions. The opposing exoergic effect of solvent donor/solute acceptor hydrogen bonding, and endoergic cavity term are the main factors influencing HPLC capacity factors.