The Equilibrium Structure of Benzene

The r e structure of benzene is revised on the basis of high-level quantum chemical calculations at the CCSD(T)/cc-pVQZ level as well a reanalysis of the experimental rotational constants using computed vibrational corrections. A least-squares fit to empirically determined B e constants yields r e ( CC ) = 1.3914 ± 0.0010 Å and r e ( CH ) = 1.0802 ± 0.0020 Å; the latter distance is significantly shorter than the best previous estimate based on experimental data. Comparison of computed r g and r z distances with experiment as well as considerations of bond lengthening due to anharmonicity are consistent with the estimated r e distance, indicating that the recommended structural parameters are very accurate.