Compensation effect in the thermodynamics of conformational equilibria

Abstract

The solvent dependence of thermodynamic parameters of conformational equilibria in trans-1,2-dichlorocyclohexane and trans-1,2-bromochlorocyclohexane was investigated by infrared absorption spectra. The results obtained show the existence of a compensation effect in the thermodynamics of conformational equilibria: the enthalpy (ΔH0) and entropy (ΔS0) differences change in the same direction when going from one solvent to another. A semi-quantitative estimation of the effect is given on the basis of the equations of statistical thermodynamics. It is shown that the temperature dependence of the ΔS0 value must be taken into account when determining the enthalpy difference of the conformers. This yields the equality of the true and observed ΔH0 values. © 1990.