Dimerization cyclic voltammetric responses

The simplest electrodimerization mechanism occurs when the species formed as the result of a first electron transfer reaction reacts with itself to form a dimer (Scheme 2.7). This mechanism is usually termed radical-radical dimerization (RRD) because the most extensive studies where it occurs have dealt with the dimerization of anion and cation radicals formed upon a first electron transfer step as opposed to the case of radical-substrate dimerizations, which will be discussed subsequently. It is a bimolecular version of the EC mechanism. The bimolecular character of the follow-up reaction leads to nonlinear algebra and thus complicates slightly the analysis and numerical computation of the system. The main features of the cyclic voltammetric responses remain qualitatively similar, however. Unlike the EC case, however, the dimensionless parameter,... 

Structurally related monomers and dimers such as in MCl2(dppf-P, P ) and [M(/i-Cl)(dppf-P,P )]2[BF4]2 (M = Pd, Pt) [315] may also show similar cyclic voltammetric responses (in terms of its shape and current). 

Cyclic voltammograms of 48 recorded in ACN solutions containing as much as fivefold excess of pyridine are almost identical to those obtained without this base89. In both cases the product of the anodic reaction is the dimer 49. Identical electrochemical responses in the presence and in the absence of pyridine imply that there are no detectable interactions between the cation radical 48 and the pyridine molecules. However, diverse transformation of the decay profiles of 48 depending on the concentration of pyridine was observed using an electron transfer stopped-flow technique. The last observation was ascribed to the interaction between 48+ and pyridine, in which the proton is extracted by the molecule of the base89. One can therefore assume that this is an example of the process for which the voltammetric measurements at conventional scan rates cannot give full information about the pathway of the electrochemical reaction. 

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