Hydrogen bonding, steric effects and thermodynamics of partitioning

Abstract

Abstract The descriptors in the Abraham solvation equation, especially the solute hydrogen bond acidity descriptor, A , have been compared to values of Δ H o and Δ S o for partitioning in the water–cyclohexane and water–octanol systems obtained by Dearden and Bresnen. It is shown that effects on Δ H o and Δ S o due to internal hydrogen bonding parallel very closely effects on A values for substituted phenols and substituted benzoic acids, thus suggesting a common structural origin. Steric effects of ortho ‐substituted methyl groups in phenols, benzoic acids and acetanilides on Δ H o and Δ S o also parallel effects on the Abraham solvation parameters. Some of these steric effects, such as those in 2,6‐dimethylacetanilide, can be very large. Both the thermodynamics of partitioning and the Abraham descriptors suggest that in 2,6‐dihydroxybenzoic acid there is only one internal hydrogen bond, and that 2‐nitroresorcinol behaves as though it had two internal hydrogen bonds. Copyright © 2006 John Wiley & Sons, Ltd.