Molecular topology and the<i>Aufbau</i>principle

Abstract

It is pointed out that the σ-bond connectivity of the carbon atoms in a hypothetical, neutral, conjugated hydrocarbon predetermines whether or not it is possible, on the basis of the Aufbau Principle, to establish a unique, ground-state, π-electronic configuration from energy levels calculated via simple molecular-orbital theory. Such ‘molecular topology’ is relevant because it influences the relative ordering amongst the eigenvalues of the associated molecular graph. It is speculated that certain hypothetical conjugated-systems may not exist because their very topology precludes their having an energy-level family which will lead to a unique, ground-state configuration, on application of the Aufbau Principle.