Quantum-chemical studies on the aromaticity of conjugated systems-II. Aromatic and anti-aromatic annulenes: The (4n + 2)-π electron rule

The LCAO-BETA method described in Part I of this series21 has been applied to the calculation of the heats of atomization of annulenes up to C30H30 and to a number of even linear polyenes. It is shown that, in the compounds of the second type, the heats of atomization are additive functions of "single" and "double" CC bond energies. The results obtained were used to investigate the aromaticity of the annulenes according to Breslow's and Dewar's definition. Hückel's rule is verified, the (4n + 2)-π electron systems showing increased stability with respect to the "localised" model compound; the (4n)-π electron annulenes on the other hand are anti-aromatic. © 1970.SCOPUS: ar.j