EPR AND FLASH-PHOTOLYSIS INVESTIGATIONS OF SOME P-QUINONE RADICAL CATIONS

EPR and flash photolysis investigations of some p-benzoquinone radical cations in a trifluoroacetic acid-trifluoroacetic anhydride solvent mixture (5:1 vol.) are reported. Coupling constants and g-values are estimated for the radical cations of p-benzoquinone, duroquinone, tetrachloro- and tetrafluoro-p-benzoquinone and anthraquinone The electron transfer rate between p-benzoquinone radical cation and N,N,N',N'-tetramethyl-p-phenylenediamine was measured by flash photolysis and found to be 4 x 10(9) dm3 mol-1 s-1. A protonation constant of 2.3 x 10(-5) dm3 mol-1 for p-benzoquinone in trifluoroacetic -acid-trifluoroacetic anhydride was found from conductivity measurements. Quantum chemical MNDO, AM-1 and ab initio calculations lead to the conclusion that the SOMO of the p-benzoquinone radical cation is sigma-type orbital.