The spin-coupled valence bond description of benzenoid aromatic molecules

Abstract

Clear theoretical evidence is presented to show that the π-electron systems of benzenoid aromatic molecules are described well in terms of localized, non-orthogonal, singly-occupied orbitals. The characteristic properties of molecules such as benzene or naphthalene arise from a profoundly quantum mechanical phenomenon, namely the mode of coupling of the electron spins, rather than from any supposed delocalization of the orbitals. Other systems considered include azobenzenes, such as pyridine, five-membered rings, such as furan, and inorganic heterocycles, such as borazine (“inorganic benzene”).

This description is furnished by spin-coupled theory, which represents the modern development of valence bond theory. The approach incorporates from the outset the chemically most important effects of electron correlation, but it retains a simple, clear-cut visuality.