Mechanistic and theoretical studies in cation radical chemistry: The cation radical mechanism of polymerization, polar vs. cation radical mechanisms, and inner sphere vs. outer space electron transfer.

摘要

Mechanistic studies in cation radical chemistry, along with supporting theoretical computations, are presented. The use of cation radicals as reactive intermediates for polymerization (a fundamentally new polymerization method) has been developed. Several bifunctional monomers were synthesized and it was found that the peak oxidation potential (E{dollar}rmsb{lcub}p{rcub}sp{lcub}ox{rcub}){dollar} needed to be in the range of 1.1-1.3 V vs. SCE in order to obtain polymers that arose from a cation radical process. If the E{dollar}rmsb{lcub}p{rcub}sp{lcub}ox{rcub}{dollar} was too high, the monomer had a tendency to deprotonate and undergo Bronsted acid catalyzed reactions instead of the desired cation radical catalyzed pericyclic reactions. Polymerization was attempted using chemical oxidation, electrochemistry and photochemistry with chemical oxidation giving the highest molecular weight polymer, electrochemistry giving low molecular weight oligomers and photochemistry giving no polymer. Model compounds were synthesized and careful analysis of the {dollar}sp1{dollar}H and {dollar}sp{lcub}13{rcub}{dollar}C NMR spectra was required in order to determine whether or not they had been generated via an acid or cation radical process. Most of the polymers had molecular weights in the range of 2,000 to 10,000 daltons with the best result being 37,000.; Detailed mechanistic and kinetic studies have been performed on the cation radical Diels-Alder reaction of a series of aryl vinyl sulfides with 1,3-cyclopentadiene catalyzed by tris(p-bromophenyl)aminium hexachloroantimonate. These studies have permitted the formulation of the detailed mechanism of this reaction and a new mechanistic tool. This tool is useful in the determination of whether a reaction proceeds by a polar or cation radical mechanism and whether an electron transfer event occurs by the inner sphere or outer sphere mechanism.