Determination of complex association constants from gas chromatograhic data

Abstract

Abstract The equilibrium constants for hydrogen bonding of a series of β-substituted alcohols with a number of monofunctional hexadecyl derivatives and dioctyl compounds have been measured by gas chromatography. For ethanol, propanol and butanol, the enthalpy and standard entropy of hydrogen bonding have also been determined. An analysis is presented on the precision and the accuracy of the data. The acceptor strengths of the proton acceptors are compared on the basis of the enthalpies and standard entropies of hydrogen bonding, and a comparison is made of the enthalpies of inter- and intra-molecular hydrogen bonding with the same proton-acceptor group. The influence of the substituents in the alcohols on the values of the association constants is investigated; evidence is presented for a mesomeric substituent effect, probably caused by intra-molecular hydrogen bonding in the substituted alcohols. It is shown that the effect of intra-molecular interaction of two substituents on partition equilibria is, formally, full analogous to the effect of intra-molecular interaction between a substituent and the reaction centre on chemical equilibria. By using the mathematical technique of factor analysis, it is shown that the factors governing substituent effects on both types of equilibria are closely related.