In anhydrous CH3CN, 4-benzoyl-N-methylpyridinium cations undergo two reversible, well- separated (Δ E 1/2~ 0.6 V) one-electron reductions in analogy to quinones and viologens. If the solvent contains weak protic acids, such as water or alcohols, the first cyclic voltammetric wave remains unaffected while the second wave is shifted closer to the first. Both voltammetric and spectroelectrochemical evidence suggest that the positive shift of the ...