A comprehensive picture of the one-electron oxidation chemistry of enols, enolates and α-carbonyl radicals: oxidation potentials and characterization of radical intermediates

Oxidation potentials of 40 enols, enolates and some selected α-carbonyl radicals are presented along with their characterization by various techniques as applicable (X-ray, EPR, ENDOR, general TRIPLE, magnetic susceptibility measurements, UV–vis, fast scan cyclic voltammetry, isotope effects). The model compounds comprise representatives of stable simple enols linked to a multitude of substituents (alkyl, alkenyl, alkynyl, aryl, heteroaryl, propargyl alcohols) and of stable simple enols of amides. The results allow to clarify the primary reaction pathway of enol radical cations as a rapid deprotonation and—if warranted by the redox potential and the strength of the oxidant—a follow-up oxidation of the resultant α-carbonyl radical to the α-carbonyl cation. Moreover, the experimental oxidation potentials were linearly correlated with AM1 computed ionization potentials after correction for solvation. The correlation allows a reliable prediction of oxidation potentials of radicals including α-carbonyl radicals. After computing redox potentials of relevant radicals, the possibility of one-electron transfer between enolates and flavin and the involvement of various radicals of ascorbic acid in oxidation processes were assessed.