H. Hombrecher, P. Margaretha
Mar 29, 1983
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Journal
ChemInform
Abstract
The photochemical behaviour of 2-Bromo-4,4-dimethyl-2-cyclohexenone (1) was studied in 2-propanol and cyclohexane. In both solvents (n-π*)-excitation followed by intersystem crossing leads to population of a low-lying triplet (T1) state, which can be quenched by 1,3-cyclohexadiene but does not undergo chemical transformation efficiently. (π-π*)-Excitation affords 4,4-dimethyl-2-cyclohexenone (2) as the only product. While in 2-propanol 2 is formed in 60% from the S2-state and in 40% from the T2-state, in cyclohexane reduction occurs exclusively from this upper triplet state. The T2-state can also be populated via energy transfer using acetone or benzene as sensitizer. The mechanistic dissimilarities for the reduction of excited 1 in either 2-propanol or cyclohexane are discussed.