The Hückel total π-electron energy puzzle

In spite of being based on drastic simplifications, the Huckel molecular orbital (HMO) quantum-mechanical model provides a reasonably good description of the properties of -electrons in conjugated molecules. The HMO approach is found to be particularly successful in the case of the total -electron energy (E), by means of which it is possible to calculate enthalpies of formation and similar thermodynamic character- istics 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.