AbstractThe redox behavior has been determined in acetonitrile solutions at a mercury and platinum electrode for 2,1,3‐benzo(group VI)diazoles, and 3,4‐disubstituted and fused 1,2,5‐thiadiazoles. The derivatives studied contained alkyl, phenyl, bromo, chloro, cyano, nitro, methylsulfonyl, and trifluoromethylsulfonyl groups. All ring systems and their derivatives are reversibly reduced initially in a one‐electron step, to their respective radical anion, but the nitro and bromo derivatives are reduced preferentially at the substituent group. The potential at which the production of the radical anion occurred became more anodic as the electron withdrawing ability of the substituent and the number of substituents in