Photoinduced reductive cleavage of some chlorobenzylic compounds. New insights from comparison with electrochemically induced reactions.

The photoinduced reductive cleavage of the carbon-chlorine bond in some chlorobenzylic nitro- and cyano-substituted compounds has been studied by transient absorption spectroscopy. The influence of the nature of the electroattractive group as well as its relative position and of the mixture composition of the solvent were investigated to give new clues into the mechanisms and into the factors that control the concerted or stepwise character of the process. Experimental results have been compared with previous results obtained by electrochemical techniques on the same molecules. Analysis leads to the conclusion that, beside the molecular structure, the solvation conditions and the driving force offered to the reaction, the formation of an excited state may control the reactivity.