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

The phototransposition (ortho, meta, para) in acetonitrile of a number (25) of disubstituted benzenes have been examined. For some cases (methylbenzon itriles, trifluoromethyltoluenes, and trifluoromethylbenzonitriles) photost ationary states could be reached but others (methylanisoles, methoxybenzoni triles dicyanobenzenes, and methy 4-toluyl sulfone) were unreactive. The ph otoaddition of 2,2,2-trifluoroethanol (TFE) to the same compounds as well a s 5 monosubstituted cases was also examined. The products obtained for reac tive compounds were all TFE ethers of bicyclo[3.1.0]hex-3-en-2-ol derivativ es. For benzene and alkylbenzenes (toluene, ortho-xylene) these photoadduct s are formed by ground state addition of TFE to benzvalene derivatives. For others (methylbenzonitriles), bicyclic diradicals or carbenes are likely i ntermediates. Many substituted compounds (anisole, fluorobenzene, methyl be nzoate, methyl anisoles, methoxybenzonitriles, dicyanobenzenes, trifluorome thylbenzonitriles, and fluorotoluenes) did not react with TFE. The trifluor omethylbenzonitriles did however undergo phototransposition in TFE, the onl y compounds to do so.