Photochemistry of some allenic counterparts of cyclohexenones and 2,5-cyclohexadienones

Article abstract of DOI:10.1021/ja00055a014

Allenic analogs of 4,4-diphenylcycIohexenone and a similar counterpart of 4,4-diphenyl-2,5-cyclohexadienone were synthesized. These molecules have a 2-electron π-MO perpendicular to the six-ring π-system. This perpendicular π-orbital is analogous to the oxygen p_y orbital which is orthogonal to the carbonyl π-bond. The photochemistry of the allenic systems was explored with the finding that the triplets were unreactive and the singlets underwent a phenyl migration to form bicyclic photoproducts whose structures were established by spectral means, degradation, and independent synthesis. Excited states involving appreciable out-of-plane to π or π to out-of-plane excitations are defined as π^- * and -π*, respectively. MNDO-CI level and CASSCF ab initio computations with geometry optimization were carried out with the objective of determining the role of -π* and π^-* transitions and for comparison with the experimental results.