Flash photolysis and electron spin resonance study of p-chloranil

Abstract
The photochemistry of p-chloranil in dioxan and in isopropyl alcohol was re-investigated by a combination of flash-optical e.s.r.-rotating sector techniques. The transient photoradical is identified as the p-tetrachlorobenzosemiquinone neutral radical based on e.s.r. and kinetic evidence. The radicals decayed by self-disproportionation with a second order rate constant of approximately 8.2 × 108 M–1 s–1 in dioxan and about 1.7 × 108 M–1 s–1 in isopropyl alcohol. The combined optical e.s.r. data yielded the following optical molar extinction coefficients for the neutral semi-quinone radicals in dioxan: 7.3 × 103 M–1 cm–1(420 nm); 7.7 × 103 M–1 cm–1(435 nm) and 6.0 × 103 M–1 cm–1(448 nm).

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