Additivity of vaporization enthalpy: Group and molecular contributions exemplified by alkylaromatic compounds and their derivatives

Abstract

Recently we proposed a system of methods for evaluation of the phase transition enthalpies of aromatic and heteroaromatic compounds, on the one hand, and aliphatic compounds, on the other. The present work is aimed at the prediction of the vaporization enthalpies of alkylaromatic compounds and their derivatives. According to the proposed approach, the vaporization enthalpy of an aliphatic compound carrying aromatic substituents can be derived from the vaporization enthalpy of an aliphatic compound, serving as a backbone, and a contribution of an aromatic fragment, which is also derived from the vaporization enthalpy of a pure aromatic compound. The additivity of the vaporization enthalpies of the fragments may fail if their combination is followed by the changes in (1) polarizability due to π-conjugation and (2) intermolecular hydrogen bonding strength. Independent procedures for accounting for both factors were proposed. The vaporization enthalpies of 174 compounds at 298.15 K were calculated and compared with the literature values. The average deviation and root-mean-square deviation were –0.2 and 1.5 kJ·mol−1, respectively, being competitive with the accuracy of experimental techniques.