LASER FLASH, LASER-DROP, AND PREPARATIVE PHOTOCHEMISTRY OF 1,5-DIIODO-1,5-DIPHENYLPENTANE - DETECTION OF A HYPERVALENT IODINE RADICAL INTERMEDIATE

Studies of the laser flash and laser-drop photolysis of 1,5-diiodo-1,5-diphenylpentane (4) support the intermediacy of a cyclic hypervalent iodine radical, 19. Radical 19 has spectroscopic and chemical properties quite different from those of typical benzylic radicals; for example, the absorption spectrum of 19 is red-shifted and significantly broader than that for the 5-chloro-1,5-diphenylpentyl radical, 14. In addition, 19 is virtually unreactive toward oxygen. Laser-drop photolysis of 4 led to further decomposition of 19 to yield primarily a mixture of isomeric 1,2-diphenylcyclopentanes (18) presumably from the corresponding 1,5-biradical. The differences and similarities between this biradical and that produced in the photolysis of 1,5-diphenylcyclohexanone (15) are discussed.