EPR studies of the structure of transient radicals formed in photolytic reactions of some 2-nitrobenzyl compounds. Characterisation of aryl alkoxy aminoxyls and nitroaromatic radical-anions in the photolysis of caged ATP and related compounds

Radical species generated on photolysis of 2-nitrobenzyl compounds, including derivatives of 1-(2-nitrophenyl)ethyl phosphate (caged ATP 1 and caged monomethyl phosphate 3) have been studied by EPR spectroscopy and their identity confirmed by independent chemical generation of the appropriate nitrogen-centred radicals. The reactions which occur include photo-isomerisation, photo-fragmentation, photo-assisted electron-transfer, intramolecular addition and spin-trapping reactions of the nitroso compounds produced via molecular rearrangement. In particular, a mechanistic scheme is advanced to explain the co-formation of a radical-anion and a cyclic aryl alkoxy aminoxyl (2 and 30, respectively, from caged ATP). Which of these species is observed in the EPR spectrum depends upon the particular experimental conditions.