Collect. Czech. Chem. Commun. 1988, 53, 1745-1752

Photochemistry of α-halocycloalkanones and α,α-dihalocycloalkanones. Ionic and radical photochemical carbon-halogen bond cleavage

Boris Šket and Marko Zupan

Department of Chemistry and J. Stefan Institute, E. Kardelj University of Ljubljana, Ljubljana, Yugoslavia


The nature of the photochemical carbon-halogen bond cleavage in α-halo cycloalkanones depends on the halogen atom bonded and on the ring size of the cycloalkanone. In the 2-halo-1-indanone series the amount of radical products increased from iodine to chlorine, while in the case of 2-halo-3,4-dihydro-1(2H)-naphthalenone 43% for iodo, 32% for bromo, and 53% for the chloro derivative were found. On the other hand, photochemical carbon-chlorine bond cleavage in 2,2-dichloro-1-indanone led to only radical products, while the formation of both radical and ionic products in the ratio 1 : 1 was observed in the case of 2,2-dibromo-1-indanone. In the 2,2-dihalo-3,4-dihydro-1(2H)-naphthalenone series, the ratio of the radical to ionic products formed strongly depended on the halogen atom bonded: preferential formation of the radical product in the case of the chloro derivative (92%), in contrast to 94% of the ionic products in the case of the bromo derivative, was observed.