The acid–base function in non-aqueous solution. Part IV. Evidence for entropy production by solvent exclusion in an aprotic solvent

Abstract

The entropies and enthalpies of some proton-transfer reactions in chlorobenzene solution have been measured spectrophotometrically. The results of these systems and some others previously measured are discussed. As the proton-transfer affinity is increased, either by increasing the strength of the acid or of the base, we find that the entropy of reaction, normally ca.–84 J K^–1 mol^–1, becomes strongly positive (ca.+76 J K^–1 mol^–1). We suggest that this is because solvent is excluded from the neighbourhood of the hydrogen bond if the latter is strong and therefore short.