The diradical nature of ketocarbenes occurring in the Wolff rearrangement. An MC-SCF study

Abstract

Using MC–SCF gradient optimisation techniques (at the 6–31G^* basis-set level) the minima and transition structures occurring in the rearrangements of formylmethylene to oxirene have been characterised. The triplet-state and singlet-state surfaces and the crossing region have been studied. The results show that the lowest-energy singlet state of formylmethylene is a pure diradical. The related triplet state has a very similar geometrical structure and lies only slightly lower in energy. Further, both states have the two unpaired electrons in sigma orbitals and the minimum-energy singlet–triplet crossing point occurs very near singlet–triplet diradical minimum of formylmethylene.