One-electron reduction studies on some aroyl/heteroacyl-1,4-benzoquinones (RCO-BQ)

A series of newly synthesized nine aroyl/heteroacyl-1,4-benzoquinones (RCO- BQ) undergoes one-electron reduction in pulse radiolytic reducing condition s in an aqueous-2-propanol-acetone mixed solvent (MS). The radical centre i s mainly located in the quinone ring, though a small probability exists for reduction at the carbonyl (CO) group. The intramolecular hydrogen bonding between the OH group of the semiquinone ring and the adjacent CO group make s the radical more stable as compared to the simple benzosemiquinone radica l. A red-shifted absorption band arises mainly due to large conjugation in the semiquinone. The substitutions (R), thiophenyl, phenyl and furanyl grou ps at the keto position reduce their one-electron reduction potential (El) values from -30 mV for BQ to < -300 mV in some of these quinones.