IS SUPERBENZENE SUPERAROMATIC

The electronic structure calculations on the kekulene (superbenzene) molecule were carried out at the HF/STO-3G and HF/6-31G** levels. The HF/6-31G** energies were also calculated for a number of benzenoid hydrocarbons. The energies were decomposed into average nodal contributions from which a "superconjugation-free" reference energy for the kekulene molecule was estimated. The computed HF energy of kekulene was found to be lower than its reference counterpart by 32.9 kcal/mol at the STO-3G level and by 25.4 kcal/mol at the 6-31G** level. This indicates the extra stabilization (superaromaticity) due to the presence of a circular formation of benzenoid rings. Geometry optimizations of the kekulene molecule at the HF/STO-3G and HF/6-31G** levels yielded planar geometries in agreement with the experimental structure. The inner hydrogen atoms are found to be linked by "weak" bonds according to Bader's theory of atoms in molecules.