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In the past, some authors [40] have questioned the radical-radical (RR) coupling mechanism on the ground that the strong coulomb repulsion between small cation radicals renders a direct dimerization of such particles improbable. Instead, they postulated a radical-substrate (RS) coupling. An electrophilic attack by the radical cation on the neutral monomer or oligomer produces the single-charged coupling product, which eliminates its protons only after a further charge transfer, becoming a neutral oligomer. However, the principal objection to the RR path-the strong coulombic repulsion between charged particles-is not convincing for reactions in solution. Using the Debye-Smoluchovski theory [41], it has been shown that even small molecules that are equally charged are able to dimerize at a diffusion-controlled rate [42]. Recently, applying the oligomer approach, several authors have demonstrated that the "dimerization" reactions of the heterocyclic monomers and oligomers involve coupling between two electrogenerated cation radicals rather than with the starting molecule [28c,32,33,38,39]. Careful quantitative kinetic studies of the coupling steps of oligomeric pyrroles and thiophenes have confirmed this mechanistic pattern [43].