ELECTROCHEMICAL OXIDATION OF 5-UNIT HETEROCYCLES - A DISCUSSION ON THE POSSIBLE DIMERIZATION MECHANISMS

Several five-ringed heterocyclic oligomers (containing thiophene and p yrrole units) have been studied by cyclic voltammetry and double-step chronoamperometry in dichloromethane. The variation of the redox poten tials with the substitution has been correlated with both electronic a nd steric effects. Most of the compounds studied have been found to el ectrodimerize by a cation radical-cation radical dimerization mechanis m, and the corresponding rate constants have been extracted. In additi on, it has been thoroughly discussed whether a possible slow deprotona tion step following the irreversible dimerization step would affect th e determination of the rate constants and also its possible effects on the apparent number of electrons exchanged per oligomer.