Ab initio quantum mechanical calculations on the singlet ground state of C2H2O have yielded geometries and rearrangement paths for ketene, hydroxyacetylene, formylmethylene, and oxirene. Geometries and rearrangement paths were determined by the single configuration self-consistent field method first by using the 4-31G basis set and then refined by using a double-ζ plus polarization basis set. Correlation energy corrections were calculated by using the configuration interaction method with a wave function which included all singly and doubly substituted configurations. The results show that hydroxyacetylene is 36 kcal/mol less stable than ketene, and there is a high barrier of 73 kcal/mol in the rearrangement path to ketene. Formylmethylene is unstable with respect to rearrangement to ketene, while oxirene is 82 kcal/mol above ketene with a small activation barrier of 2 kcal/mol for rearrangement to formylmethylene. These results together with preliminary results obtained for excited-state surfaces are used to elucidate the mechanism of the Wolff rearrangement. An analysis of the effects of polarization function and correlation energy on relative energy is also carried out to assess the accuracy of the results. © 1980, American Chemical Society. All rights reserved.