Photochemistry of 4,4-Dimethyl-1-phenyl-2-pentyn-1-one

Article abstract of DOI:10.1021/jo00274a039

The photochemistry of 4,4-dimethyl-1-phenyl-2-pentyn-1-one has been examined by a combination of laser flash photolysis experiments and product studies.The triplet ketone is relatively long-lived in inert solvents such as acetonitrile but reacts readily with hydrogen donors via hydrogen abstraction to give the corresponding ketyl radical and with substituted aromatics via charge-transfer quenching.For example, rate constants for quenching by cyclohexane and anisole are 2.9 x 10⁷ and 2.8 x 10⁸ M^-1s^-1, respectively, in acetonitrile.The ketone undergoes efficient photodecomposition in cyclohexane (Φ=0.86) to give the expected radical coupling products but is unreactive in benzene.The ketone radical anion (λ_max = 510 nm in acetonitrile) is formed directly by quenching the triplet with 1,4-diazabicyclo<2.2.2>octane.It may also be generated indirectly in the reaction with triethylamine by reduction of the parent ketone by the amine-derived radical produced by hydrogen abstraction by the triplet ketone.