The 1e-,2H+ electrochemical reaction (six-member ladder scheme) is studied when the protonations are at equilibrium, and when the reaction products undergo irreversible dimerizations. The results are valid for a surface reaction (adsorbed species, Langmuir isotherm), or for a heterogeneous reaction. If the symmetry factors of the elementary electrochemical reactions are equal to 0.5, the system behaves as a simple monoelectronic process, with an apparent rate constant k(eapp), followed by a dimerization with an apparent constant k(app). The expressions of the variations of k(app) with pH are established : they allow discrimination between the diverse types of dimerizations.