AM1 and PM3 semi-empirical study of the Diels–Alder reaction between N-, P-, O- and S-substituted aromatic heterocyclic five-membered rings with acrolein

Abstract

A semi-empirical study of the effect of substituent on the HOMO–LUMO energies of the 3,4-disubstituted five-membered heterocyclic aromatic compounds, the equilibrium constants of the Diels–Alder reaction of N-, P-, O- and S-substituted heterocyclic five-membered aromatic rings with acrolein and 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 E LUMO of the diene and σ p and σ m of 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 σ p and σ m, as expected for linear free energy relationships.