The Wolff Rearrangement: The Relevant Portion of the Oxirene-Ketene Potential Energy Hypersurface

The portion of the C[sub 2]H[sub 2]O potential energy hypersurface that includes oxirene, formylmethylene, and ketene has been studied with ab initio methods incorporating high levels of electron correlation and basis sets that include up to f and g functions. Our best geometries were determined at the CCSD(T)/6-3 UG(df,p) level of theory. Single-point energies were then determined by using CCSD(T) and BD(T) calculations with the cc-pVTZ basis set augmented with additional f and g polarization functions. Our main conclusion is that there is little or no barrier separating formylmethylene from oxirene, the potential energy surface linking these two species begin extremely flat. On the other hand, a more significant barrier (21-23 kJ mol[sup [minus]1]) separates formylmethylene or oxirene from ketene. These results strongly support the previously postulated intermediacy of oxirene in the Wolff rearrangement. Ketene is found to lie 325 kJ mol[sup [minus]1] lower in energy than oxirene. Our predicted energy threshold for the scrambling of carbon atoms in ketene (348 kJ mol[sup [minus]1]) is in close agreement with a recent experimental value (340 kJ mol[sup [minus]1]). 42 refs., 5 figs., 3 tabs.