Equilibrium structure of gas phase o-benzyne

An equilibrium structure has been derived for o-benzyne from experimental rotational constants of seven isotopomers and vibration-rotation constants calculated from MP2 (full)/6-31G(d) quadratic and cubic force fields. In the case of benzene, this method yields results that are in excellent agreement with those obtained from high quality ab initio force fields. The ab initio-calculated vibrational averaging corrections were applied to the measured A0, B0 and C0 rotational constants and the resulting experimental, near-equilibrium, rotational constants were used in a least squares fit to determine the approximate equilibrium structural parameters. The C-C bond lengths for this equilibrium structure of o-benzyne are, beginning with the formal triple bond (C1-C2): 1.255, 1.383, 1.403 and 1.405 Å. The bond angles obtained are in good agreement with most of the recent ab initio predictions.