Photoinduced hydrogen abstraction reaction of 2,6-dichloro-p-benzoquinone studied by time-resolved electron spin resonance

Abstract

Steady-state and time-resolved ESR spectra of the dichloro-p-benzosemi-quinone (DCSQ) radicals were measured in the photochemical hydrogen abstraction reaction of 2,6-dichloro-p-benzoquinone (2,6-DCBQ) in chloroform at room temperature. The 2,6-DCSQ radical was observed by steady-state ESR and the magnetic parameters (hyperfine coupling constants and g values) were obtained from its high resolution steady-state ESR spectrum and a computer simulation. The chemically induced dynamic electron polarization (CIDEP) signals of the 2,6- and 3,5-DCSQ radicals were obtained in sub-microsecond time regions after laser excitation of the chloroform solution of 2,6-DCBQ, and were explained by a combination of the radical pair mechanism and the triplet mechanism of CIDEP. The CIDEP signals of the 3,5- and 2,6-DCSQ radicals disappeared with different decay rate constants of (1·57 ± 0·2) × 106 s-1 and (1·10 ± 0·1) × 106 s-1, respectively. These results show that two types of radical (2,6- and 3,5-DCSQ) are produced indiv...