SUBSTITUENT EFFECTS ON HYDROGEN BONDING AND RATE-DRIVING FORCE RELATIONSHIPS IN N—H OXIDATIVE PCET REACTIONS

Abstract

Oxidative proton-coupled electron transfer (PCET) of amides has been shown to be influenced by hydrogen bonding and preliminary studies have indicated that substrate affects may influence reaction kinetics. Herein we present an investigative study on observed effects to hydrogen bonding equilibrium constants and PCET rate constants in response to substrates with different atoms α to the carbonyl and different para- aromatic substituents. Hydrogen bonding equilibrium was found to vary with this α-atom, decreasing over two-fold when a carbon atom was replaced with an oxygen. Slopes of rate-driving force relationships were smaller than predictions from Marcus theory predictions. Rationalization of this discrepancy is ascribed to either asynchrony or non-perfect synchronization. No change in slope was observed with the addition of steric hindrance to thiophenol substrate.