SOLVENT HARD-SPHERE DIAMETER FROM VANDERWAALS VOLUME - A STATISTICAL-ANALYSIS OF COMPUTED AND SOLUBILITY DETERMINED SOLVENT DIAMETERS

Hard sphere diameters (d(HS)) of solvent molecules are useful quantiti es in evaluating the effect of the solvent by means of scaled particle theory, but they can be obtained only through elaborate experiments. It is shown here that d(HS) can be conveniently replaced with the diam eter of van der Waals equivalence sphere (d(V)). Deviations were found in such replacements for polar, hydrogen-bonding and long-chain hydro carbon solvents, and a procedure is proposed to obtain the contact cor relation function for a real solvent, used to evaluate the reversible work for cavity formation, by multiplying the contact correlation func tion of a hard sphere solvent with a correction factor. The factors ar e derived from the static dielectric constants for the polar (H-bondin g) solvents, and from the molecular shape indices for the long-chain a lkane solvents. The relationship between the correction coefficient an d the macroscopic dielectric constant for polar solvents suggests that the dielectric continuum-medium model of the solvent may include solv ent-solvent repulsive interactions through the experimentally determin ed dielectric constant. The final correlation coefficient between expe rimental d(HS) and the computed d(V) is 0.992 for a series of 44 solve nts. Our results suggest close correspondence between the solid packin g and solution structure at the microscopic level. (C) 1998 Elsevier S cience B.V. All rights reserved.