PHOTOCHEMISTRY AND RADIATION-CHEMISTRY OF BENZOCYCLOBUTENONE - FORMATION OF AN O-QUINOID KETENE AND ITS RADICAL CATION

Upon X-ray irradiation of benzocyclobutenone (BCB) in an Ar matrix, the valence isomeric o-quinoid vinylketene (QK) is formed efficiently next to its radical cation (QK+.) which is characterized for the first time by its UV/vis and IR spectrum. It is argued that QK arises by the neutralization of QK+. which forms spontaneously upon ionization of BCB in Ar. The mechanism of the facile BCB+. --> QK+. rearrangement is discussed on the basis of semi-empirical and ab initio quantum chemical calculations.