X-RAY-INDUCED TRANSFORMATION OF O-VINYLBENZALDEHYDE AND 2-METHYLBENZOCYCLOBUTENONE TO AN O-QUINOID KETENE AND ITS RADICAL-CATION

Upon ionization in argon matrices by X-irradiation, o-vinylbenzaldehyd e (VBA) partially undergoes transfer of the formyl hydrogen atom to th e vinylic CH2 group, thereby forming a quinoketene radical cation of t he type previously described (Bally, T.; Michalak, J. J. Photochem. Ph otobiol. A: Chem. 1992, 69, 185). This process does not manifest itsel f clearly in the optical spectra because the transitions of the quinok etene cation coincide with the much more intense ones of VBA(.+) and a re mostly obscured by those. However, the IR spectra show unambiguousl y that the rearrangement occurs rather efficiently. Also they show tha t in the course of the X-irradiation, the tautomerized cations are ren eutralized to from the quinoketene tautomer of VBA in good yield. The quinoketene and its radical cation were independently obtained from 2- methylbenzocyclobutenone which undergoes spontaneous ring-opening on p hotolysis and/or ionization. The optical spectra of the radical cation s are assigned on the basis of CASPT2 calculations and the different s pecies involved in this study are characterized at the B3LYP/6-31G le vel.