Hordieieva I. The reactivity of N oxyl radicals in the H atom abstraction reactions from molecules of benzyl alcohols

A predictive model for the rate constants of hydrogen atom transfer (HAT) from the a-C-H bond of p-substituted benzyl alcohols by N-oxyl radicals of different structures is proposed. A multivariate regression analysis was carried out to quantitatively evaluate the factors that control the reactivity of N-oxyl radicals and benzyl alcohols using various combinations of the reactivity parameters of the reagents. The regression analysis was based on a 2D array of 35 HAT reactions, the rate constants of which varied in the range of 4 orders. The proposed final polyparameter equation approximates with high reliability the experimental rate constants of reactions when using three independent parameters: Brown-Okamoto σ+ constants of substituents in alcohol molecules and the spin populations on O and N atoms of N-O fragments in N-oxyl radicals, which calculated by method DFT/B3LYP/6-31G(d,p). The absolute rate constants of HAT reactions from para substituted benzyl alcohols by a series of aryl-substituted phthalimide-N-oxyl radicals containing either electron-withdrawing groups (4-Cl, 4-HOOC) or electron-donating group (4-CH3O), quinolinimide-N-oxyl, benzotriazole-N-oxyl and violuric acid radical were experimentally determined at 30 ℃ in acetonitrile.