Steric and Electronic Effects in Methyl-Substituted 2,2‘-Bipyrroles and Poly(2,2‘-Bipyrrole)s:  Part I. Synthesis and Characterization of Monomers and Polymers

The effects of N - and C -methyl substitution on electrical and spectral properties of pyrrole, 2,2‘-bipyrrole, and the corresponding polymers were investigated. The whole series of monomethyl and N - or C β -dimethyl-substituted 2,2‘-bipyrroles was synthesized, and the electrochemical and spectral properties of all the compounds were investigated under identical testing conditions. The corresponding polymers were prepared by electrochemical anodic oxidation under comparable experimental conditions and their spectroscopic and conductivity properties evaluated for comparison. The higher degree of efficiency in transmission of electronic effects associated with methyl substitution at C β with respect to substitution at N was clearly demonstrated. The influence of the symmetry of the starting monomer ( C 2 v or C s ) on the electrical properties of the resulting polymers is discussed.