This grant in the Organic and Macromolecular Chemistry Program supports research by Prof. W. Bentrude, which aims at elucidating mechanisms in chemical reactions of organophosphorus systems with free radicals as reaction intermediates. This work is important for two reasons: (1) It will provide understanding of the step- by-step processes by which certain phosphorus-containing organic molecules react to generate unpaired-electron-intermediates (free radicals) when excited by light absorption and other energizing events; and (2) many of these reactions may be used as synthetic methods for preparation of sensitive compounds. Studies of both free radical and photochemical reactions of organophosphorus molecules are planned. Both new investigations and new aspects of reactions discovered in the previous grant period will be pursued. A major theme is the design and investigation of reaction systems in which true biradicals or biradical-like electronic excited states react with tricovalent phosphorus in intra- or intermolecular processes. Mechanistic, exploratory new-reaction, and synthetic aspects of these systems are to be examined. Reactants included in this work are photoexcited alkenes, alkynes, allenes, carbonyls, and thiocarbonyls, along with biradicals from Norrish Type I photocleavage reactions and the photolyses of azo compounds. In addition, new reactions in which intact phosphoranyl radicals are trapped will be studied. The mechanistic aspects and synthetic applications of the intramolecular photo-Arbuzov reaction of benzyl phosphites, newly discovered in Bentrude's laboratory, will be explored. Also to be thoroughly studied is the photosolvolysis of benzyl phosphites in the presence of alcohols. Its mechanism and generality using other chromophores and leaving groups will be assessed.
