Photoinduced Paramagnetism in Solutions of Nitrobenzene in Tetrahydrofuran

ESR studies are reported of photoinduced paramagnetism in solutions of nitrobenzene in undeuterated and deuterated tetrahydrofuran (THF). The ESR spectrum exhibits a widely spaced set of identical triplets, and the extra proton hyperfine interaction (0.38 plus or minus 0.04 Oe) is due to a single alpha proton of the THF molecule. The experiments of Lagercrantz and Yhland with trinitrobenzene were also repeated, and the following mechanism for the production of the paramagnetic species is proposed: Light irradiation causes the nitro group to abstract an alpha hydrogen atom from the THF molecule, and the resulting THF free radicais rapidly dimerize or disproportionate, leaving a neutral nitrobenzene free radical in solution. The radical has a totai decay time of approximates 2 sec and is suspected to reside on an oxygen atom. (D.L.C.)