THE ELECTRON SPIN RESONANCE ABSORPTION SPECTRA OF SEMIQUINONE IONS: PART III. FREE RADICAL SALTS OF QUINHYDRONES

Electron spin resonance absorption was observed in alkali salts of tetrachloro-p-benzoquin-hydrone, p-biphenoquinhydrone, and its tetrachloro and tetrabromo derivatives. The magnitude of g-value was found to be in the order of unsubstituted < chloro derivative < bromo derivative, and benzoquinhydrone salt < the corresponding p-biphenoquinhydrone salt. The frequency of C—O stretching vibration was observed in the range 1525 to 1550 cm−1. Based on these frequencies the estimation of the parameters which are necessary for the molecular orbital treatment of semiquinone ions was attempted. A set of αO = α + (l/3−l/2)β and βCO = β were derived. Independently values of αO = α + 2/3β and βCO = β were estimated using the hyperfine structure of the electron spin resonance spectrum of the α-naphthosemiquinone ion.