The McClelland approximation and the distribution of π-electron molecular orbital energy levels

摘要

The total π-electron energy E of a conjugated hydrocarbon with n carbon atoms and m carbon-carbon bonds can be approximately calculated by means of the McClelland formula E ≈ g 2mn, where g is an empirical fitting constant, g ≈ 0.9. It was claimed that the good quality of the McClelland approximation is a consequence of the fact that the π-electron molecular orbital energy levels are distributed in a nearly uniform manner. It will now be shown that the McClelland approximation does not depend on the nature of the distribution of energy levels, i.e., that it is compatible with a large variety of such distributions. .