A semi-empirical study of the thermodynamics of the Diels-Alder reactions of N, P, O, and S substituted five membered heterocyclic aromatic rings with acrolein /

Abstract

A semi-empirical study of the effect of substituent on the HOMO-LUMO energies of the 3,4 disubstituted 5-membered heterocyclic aromatic compounds, on the equilibrium constants of the Diels-Alder reaction of N, P, 0 and S substituted heterocyclic 5-membered aromatic rings with acrolein, and on the enthalpy change of the reactions, gave results in accordance with the familiar Diels-Alder reaction. A linear correlation was found between E HOMO and ELUMO of the diene and (Jp and (Jm of the Hammett equation. The log of the equilibrium constant calculated from the computed enthalpy and entropy of the reactions at 298 K, and the reaction enthalpy itself, also correlated with (Jp and (Jm, as expected for linear free energy relationships.