The polarographic reduction potentials E1/2 of the pyrazinium, quinoxalinium, benzoquinoxalinium, pyrido[2,3-b]pyrazinium, and pteridinium cations were determined. Annellation of a benzene ring increases the electrophilicity of the diazinium cations to a greater degree than the introduction of such electron acceptors as aza, aminocarbonyl, or methoxycarbonyl groups. The boundary between the active and inactive 1,4-diazinium salts was determined; cations with E1/2 values more negative than −0.50 V do not form either stable covalent adducts or cyclic diadducts through annellation of the dinucleophiles to the pyrazine ring.