On the basis of voltammetric behaviors obtained for the electrochemical reduction of a series of alpha-NH-quinones (Q) of increasing basicity (5H-benzo[b]carbazole-6,11-dione (BCD), 2-{[4'-(trifluoromethyl)phenyl]amine}-1,4-naphthalenedione (p-CF(3)PAN), 2-(phenylamine)-1,4-naphthalenedione (PAN), 2-[(4'-methoxyphenyl)amine]-1,4-naphthalenedione (p-MeOPAN), and 2,5-di(alpha-methylbenzylamine)1,4-benzoquinone (DMeBABQ)), in the presence of additives with increasing acidity [ethanol (EtOH), phenol(PhOH), benzoic acid (HBz), perchloric acid (HClO4)], it was possible to identify some of the species present in the diffusion kinetic layer, allowing to control the protonation steps and/or hydrogen bond formation prior to and/or following the electron transfer processes. EtOH and PhOH act as hydrogen bonding donors with the corresponding semiquinone radical anion, (Q(.-)), and dianion hydroquinone, (Q(2-)), electrogenerated species. Due to the low acidity level of EtOH, the hydrogen bonding association process was detected only for [EtOH]/[Q] ratio > 100; meanwhile, with PhOH a strong hydrogen bonding process was detected, even at 0.3 equivalents of PhOH. The diagrams of average number of "ligands" (n(av)) vs. log [EtOH]/[Q] for Q(.-)(EtOH)(n) and Q(2-)(EtOH)(m) complexes were constructed using the successive association constants obtained from the experimental half-wave potential displacements. These diagrams show that the maximum number of molecules of EtOH hydrogen bonded to Q(.-) and Q(2-) directly depends on the basicity of the corresponding quinone. With HBz, the voltamperometric behavior shows the direct protonation of the electrogenerated Q(.-) provoking a typical electrochemical-chemical-electrochemical mechanism, with "the chemical step" being a proton transfer. Finally, the use of a completely dissociated acid HClO4 in acetonitrile solution, allowed to observe the successive interaction of protons with each of the different species appearing in the quinone/hydroquinone systems, including mono- and di-protonation of the neutral quinones. (C) 2004 The Electrochemical Society.