In this work, it is considered that charged molecules, such as the semiquinone (Q .À ) and the benzoquinone dianion (Q 2À ), interact with weak donor protons (DH) via hydrogen bonding through consecutive association steps which depend on the concentration of DH. On the basis of a reversible voltammetric behavior, a model is presented for determining integer numbers of associated molecules of DH and the thermodynamic constants (b i ) related with each association equilibrium. The electrochemical reduction of 1,4-benzoquinone (Q) in the presence of different aliphatic alcohols and diols, in dimethylsulfoxide (DMSO), illustrates the utility of the model. Based on analysis of half-wave potential variation according to the DH concentration, the association constants were determined for the Q .À and Q 2À complexes with the different alcohols studied and mole-fraction distribution diagrams were constructed. These diagrams explain the fractional values, produced using the typical model, widely reported in the literature, for study the hydrogen bonding between the electrochemically generated charged species with donor protons.

The study of the electrochemical reduction of several quinones, Q, in the presence of alcohols, n­ROH, and diols, 1,n­Rfalse(OH)2, with different chemical structures is reported. From the stoichiometry and the formation constants of the different association complexes, obtained from voltammetric results, mole-fraction distribution and average-number-of-ligand diagrams were constructed to analyze structural effects on hydrogen bonding association between the quinone dianion species and the alcohols. It was demonstrated that the association process can be determined by the quinone basicity, steric effects, and by the α-hydrogens in the quinone nucleus. The quinone basicity determines the strength of the association process when no α-hydrogens are present. Meanwhile, the strength of this interaction is intensified when the number of α-hydrogens is increased in the quinone nucleus. The passage from a situation of an association sterically controlled to a situation controlled by the basicity of the quinone can be modulated with the structure and the amount of the hydrogen-bonding donor present in the medium. © 2003 The Electrochemical Society. All rights reserved.

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