The photoequilibration of the ortho-, meta-, and para-isomers of substituted benzenes in ace- tonitrile and the photoaddition of 2,2,2-tri- fluoroethanol (TFE) to the same isomers: a survey

Abstract

The phototransposition (ortho, meta, para) in acetonitrile of a number (25) of disubstituted benzenes have been examined. For some cases (methylbenzonitriles, trifluoromethyltoluenes, and trifluoromethylbenzonitriles) photostationary states could be reached but others (methylanisoles, methoxybenzonitriles, dicyanobenzenes, and methy 4-toluyl sulfone) were unreactive. The photoaddition of 2,2,2-trifluoroethanol (TFE) to the same compounds as well as 5 monosubstituted cases was also examined. The products obtained for reactive compounds were all TFE ethers of bicyclo[3.1.0]hex-3-en-2-ol derivatives. For benzene and alkylbenzenes (toluene, ortho-xylene) these photoadducts are formed by ground state addition of TFE to benzvalene derivatives. For others (methylbenzonitriles), bicyclic diradicals or carbenes are likely intermediates. Many substituted compounds (anisole, fluorobenzene, methyl benzoate, methyl anisoles, methoxybenzonitriles, dicyanobenzenes, trifluoromethylbenzonitriles, and fluorotoluenes) did not react with TFE. The trifluoromethylbenzonitriles did however undergo phototransposition in TFE, the only compounds to do so.Key words: substituted benzenes, phototransposition, photoaddition.