Thermodynamics of some model reactions useful for understanding theoretical background of correlation analysis

Abstract

Six isodesmic gas-phase reactions have been studied out of which three reactions represent a redistribution of two methyl substituents and the other three represent a redistribution of two chloro substituents between two benzene nuclei. The thermodynamics of these reactions has been evaluated on the basis of the partition functions and observed heats of formation at room temperature. The partition functions have been constructed with the help of observed structural and vibrational data. If the internal rotation was present, the frequence of the corresponding torsional vibrational mode has been determined by a fit to the observed thermodynamic data.The energy characteristic calculated for these reactions (the standard change of Gibbs free energy ΔGT0, enthalpy ΔHT0, enthalpy at absolute zero ΔH00, and potential energy change ΔE) have been evaluated from the standpoint of their applicability to organic correlation analysis. The studies form a part of a wider project, and, in accordance with the findings already presented within this project elsewhere and concerning reactions of fluorobenzenes, they indicate a certain preferred role of the term ΔH00 in these contexts.