Trans-cis photoisomerization of 14C-labelled 1,3-diphenylpropenes. Part 2.—Sensitized photolysis

Abstract

Trans-1,3-diphenyl[1-¹⁴C] propene and cis-1,3-diphenyl [3-¹⁴C] propene and their inactive counterparts were photolysed in benzene at 365 nm in the presence of acetophenone (at 60°C and at room temperature) and Michler's ketone as sensitizers. The cis-trans isomerization can be explained within the mechanistic framework given for the stilbenes. Accompanying the cis-trans isomerization, there is a transposition of the ¹⁴C from the 1 to 3 position or vice versa; this transposition is interpreted as being caused by a [1,3] allylic shift on the olefin triplet. The observed effects on temperature changes are consistent with the proposed interpretation.