Simple model for nonassociative organic liquids and water

A simple model that has been derived from molecular-level considerations (J. Phys. Chem. B 1998, 102, 5715) is revisited and extended. It is shown that it gives a unified and adequate description of a variety of properties related to intermolecular interactions, including boiling point, enthalpy of vaporization, vapor pressure, surface tension, and a number of partition and solubility data for organic liquids that do not contain associative or strongly polar substituents. All corresponding equations were derived from the same free energy expression that forms the basis of the model. For the organic liquids considered here that include haloalkanes, aromatics, haloaromatics, eaters, and ketones, molecular size as the sole descriptor (characterized here by molecular volume) can account for 80-90% of the variance. Furthermore, water, which is a highly abnormal liquid, seems to be integrable within the model by a simple modification of the interaction-related constant. This modification is consistent with the modified hydration-shell hydrogen-bond model of Muller, with data on partition and solubility in water, and with the large surface tension value of water. Within this approach, the controversy related to different macroscopic/microscopic free energies of interactions per surface area that was raised by Tanford and has recently resurfaced in the work of Honig, Sharp, and co-workers is also avoided.