Intramolecular hydrogen bond and molecular conformation. Part 3.—Effect of temperature and pressure on the IR spectra of o-halophenols in dilute solutions

Abstract

The effects of temperature and pressure on the IR OH stretching bands of o-halophenols in dilute solutions with various solvents have been examined. From an analysis of the relative band intensities as functions of temperature and pressure, changes in enthalpy and in partial molar volume due to breakage of an intramolecular hydrogen bond have been obtained. The relative stability of the hydrogen-bond-free trans conformer compared with the hydrogen-bonded cis conformer increases with increasing solvent polarity. The partial molar volumes of the trans conformers are smaller than those of the cis conformers by the same extent irrespective of the solvent polarity. These facts have been discussed on the basis of a dielectric model of solvation.