PHOTOCHEMISTRY OF HALOKETONES-I. REACTIONS OF SOME α-HALOCYCLOHEXANONES

Article abstract of DOI:10.1016/S0040-4020(01)97653-7

α-Halocyclohexanones 1-4 on irradiation in cyclohexane have been found to involve competing radical and ionic photo-behaviour.The principal photoprocess observed in α-chloro-, α-bromo-, α-iodo-cyclohexanones was homolytic β-cleavage of carbon-halogen bond to afford radical products.These were usually accompanied by ionic products such as cyclohexenones, but in much lower proportions.Photo-Favorskii type ring contraction reported recently for α-chlorocyclobutanones was found to be completely absent.Sensitisation and quenching studies indicate that radical cleavage occurs from n-?^* triplet states whereas ionic cleavage could be a singlet derived reaction; thus providing for the first time experimental support to the proposed Wagner-model for the cleavage of carbon-halogen bond in α-haloketones.