Electron spin resonance and kinetic study of the photolysis of p-Flouranil (tetrafluoro-p-benzoquinone) in dioxane

The photochemistry of p-fluoranil in dioxane was studied by electron spin resonance (ESR) and the ESR-rotating sector technique. The transient photoradical is identified as the p-tetrafluorobenzosemiquinone neutral radical with a hyperfine splitting of 1.1 gauss for the hydroxy proton and the fluorine hyperfine splittings of 3.8 and 14.1 gauss for the meta and ortho fluorines, respectively. The radicals decayed by self-disproportionation with a second-order rate constant at room temperature of approximately 3.2 × 10⁹M^?1s^?1. The activation energy of the decay process is found to be about 2.4 ± 0.4 kcal/mole.