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The type II photoelimination reaction of a series of -aminoacetophenones has been studied. Quantum yields and rate constants for product formation were determined in several solvents. These ketones were found to undergo photoelimination with extraordinarily high rates but with modest quantum efficiency. Photoelimination of «-amino ketones with low-lying -* triplet states also occurs with enhanced reaction rates. Attachment of an electron-withdrawing benzoyl group to the nitrogen atom decreases the rate of photoelimination. The results can best be rationalized by an electron-transfer route for which the rate constant may exceed diffusion control.tudies of the photochemistry of ketones that possess a hydrogen-bearing y carbon have shown that two major reaction pathways are available.2-21 The (1) Alfred P. Sloan Foundation Research Fellow, 1968-1970 (2) This work was presented in part at the 161st National Meeting of the American Chemical Society, Los Angeles, Calif., March 1971. the formation of cyclobutanols.23 Both reactions appear to be intramolecular with little or no detectable side reactions and have been visualized as arising from a common biradical intermediate. In the case of aryl alkyl ketones, both reactions proceed by way of a triplet which leads to a 1,4-biradical intermediate which may either cyclize, undergo cleavage, or revert to starting ketone by reabstraction of hydrogen. The lines of evidence implicating the reversibility of the hydrogen transfer step are based on kinetic data4 24 and are reinforced by stereochemical25•26 and deuterium isotope ef-

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