Hydrogen Atom Transfer from Benzyl Alcohols to <i>N</i>-Oxyl Radicals. Reactivity Parameters
О. V. Kushch, I. O. Hordieieva, M. O. Kompanets, Olha O. Zosenko, I. A. Opeida, A. N. Shendrik
Abstract
A model for predicting the rate constants of hydrogen atom transfer (HAT) from the α–C–H bond of p-substituted benzyl alcohols to N-oxyl radicals was proposed. To quantify the factors governing the reactivity of both N-oxyl radicals and benzyl alcohols, multivariate regression analysis was performed using various combinations of reactivity parameters. The analysis was based on a 2D array of 35 HAT reactions, the rate constants of which span 4 orders of magnitude. The proposed polyparameter equation approximates the experimental rate constants of reactions with high accuracy using three independent parameters: Brown and Okamoto’s substituent constants σ+ in alcohol molecules and the spin population on O and N atoms in the N–O• fragment of N-oxyl radicals [calculated by DFT/B3LYP/6-31G(d,p)]. The rate constants of HAT reactions from p-substituted benzyl alcohols to a series of aryl-substituted phthalimide-N-oxyl radicals containing either electron-withdrawing or electron-donating substituents (4-Cl, 4-HOOC, 4-CH3O), quinolinimide-N-oxyl, benzotriazole-N-oxyl, and violuric acid radicals were experimentally determined at 30 °C in acetonitrile.