Kinetic Solvent Effects on Hydrogen-Atom Abstractions:  Reliable, Quantitative Predictions via a Single Empirical Equation¹

The rate of hydrogen-atom abstraction from XH by a radical, Y•, can be solvent-dependent. In many cases, the kinetic solvent effect (KSE) is directly related to hydrogen-bonding interactions between XH and the solvent. The relative hydrogen-bond acceptor (HBA) properties of solvents are given by constants of Abraham et al. (Abraham, M. H.; Grellier, P. L.; Prior, D. V.; Morris, J. J.; Taylor, P. J. J. Chem. Soc. Perkin Trans. 2 1990, 521−529). Room-temperature rate constants for hydrogen-atom abstraction, , have been determined in a number of solvents, S, where XH refers to several substituted phenols, tert-butyl hydroperoxide or aniline and Y• is a tert-alkoxyl radical. In all cases, plots of log( /M-1 s-1) versus gave excellent linear correlations, the slopes of which, MXH, were found to be proportional to the hydrogen-bond-donating (HBD) ability of XH, as scaled with parameters of Abraham et al. (Abraham, M. H.; Grellier, P. L.; Prior, D. V.; Duce, P. P.; Morris, J. J.; Taylor, P. J. J. Chem. Soc., Per...