Carbon−Carbon Bond Fragmentation in Aminoalcohol Radical Cations. Kinetics, Thermodynamic Correlations, and Mechanism

A detailed study of the kinetics, thermodynamics and mechansim of carbon−carbon bond fragmentation in a series of aminoalcohol radical cations is presented. The compounds that provide the basis for this investigation are derived from the parent structure, erythro-2-(phenylamino)-1,2-diphenylethanol, by substitution at the para position of the N-phenyl with methoxy, methyl, (hydrogen), chloro, and cyano groups (compounds 1a−e, respectively). The rates for C−C bond fragmentation for radical cations 1a−e•+ in CH3CN solution were determined by laser flash photolysis and vary from 3.9 × 104 (1a) to 7.4 × 106 s-1 (1e). The activation parameters for bond fragmentation in 1c−e•+ are characterized by low activation enthalpies and relatively large, negative activation entropies. The bond fragmentation rates increase with the peak potential for anodic oxidation of the neutral aminoalcohols, Ep(1). Correlation of the free energy of activation for bond fragmentation (ΔGBF⧧) with FEp(1) (F is the Faraday constant) impl...