ELECTROCHEMICAL STUDIES OF THE OXIDATION OF STERICALLY HINDERED PYRROLES AND THIOPHENES

The electrochemical oxidation of several alpha,alpha'-di-tert-butyl py rroles and thiophenes has been investigated in acetonitrile. Reversibl e cyclic voltammograms for the oxidation of one-ring alpha,alpha'-di-t ert-butyl thiophenes or pyrroles were obtained at low scan rates (0.05 -5 V s(-1)), indicating a large stability of their cation-radicals. Ch emical evolutions without polymerization of the cation-radical were ob served at longer time scales. The formal potentials E degrees and elec tron exchange standard rate constants k(s) were determined and compare d with preceding reports for the unsubstituted analogues. From the sub stituent variations, the E degrees values for the oxidation of the uns ubstituted thiophene and bithiophene were estimated as +1.97 and +1.49 V(SCE) respectively.