The Hückel total π-electron energy puzzle

Abstract

In spite of being based on drastic simplifications, the Hückel molecular orbital (HMO) quantum-mechanical model provides a reasonably good description of the properties of π-electrons in conjugated molecules. The HMO approach is found to be particularly successful in the case of the total π-electron energy (E), by means of which it is possible to calculate enthalpies of formation and similar thermodynamic characteristics of conjugated compounds. In this paper it is shown that expressions equivalent to E can be deduced within much more accurate quantum mechanical considerations. This might explain why E agrees so well with experimental findings.