MOLECULAR SIZE-BASED MODEL TO DESCRIBE SIMPLE ORGANIC LIQUIDS

A simple, molecular size-based model is presented that allows unified description of solubilities, partition coefficients, vapor pressures, enthalpies of vaporization, and boiling points for a variety of simple organic liquids where no specific interactions are present. A free en ergy expression obtained from specific, molecular-level assumptions is used. This makes it unnecessary to rely on standard state and activit y concepts, and it also leads to relations that cannot be obtained fro m purely thermodynamic arguments. Molecules in the liquid phase are co nsidered as moving in a fraction of the volume not excluded by their o wn size and in an average attractive potential of the surrounding mole cules that can be described by molecular volume through a simple, line ar relationship. These assumptions allow the development of a model th at gives unified and reasonably good description of organic liquids th at have no hydrogen bonding or strongly polar substituents. In practic ally all of the individual correlations presented, molecular size alon e as measured by computed van der Waals molecular volume, accounts for more than 90% of the variance in these properties. In addition, inter action constants derived from enthalpies of vaporization can describe not only boiling points but partition and solubility properties as wel l. A previously described, fully computerized method that estimates oc tanol-water partition properties for a large variety of organic solute s (Bodor, N.; Buchwald, P. J. Phys. Chem. B 1997, 101, 3404) can also be integrated within this approach.