SOLVENT EFFECTS IN THE HYDROGEN ABSTRACTIONS BY TERTBUTOXY RADICAL - VERACITY OF THE REACTIVITY SELECTIVITY PRINCIPLE

The Hammett correlations and primary deuterium kinetic isotope effects were obtained to investigate the solvent effects on hydrogen abstractions from thiophenols, phenols, and toluenes by tert-butoxy radical, where the latter proved to be a more sensitive probe than the former. The limitations of the reactivity/selectivity principle are discussed in terms of either anti-Hammond effects or Marcus theory and attributed to the duality in substituent (solvent) effects, that is thermodynamic substituent (solvent) effects differing from kinetic substituent (solvent) effects. While the polar transition states for the homolytic reactions should invite dual substituent effects, the dual solvations of tert-butoxy radical could trigger the dualism of solvent effects. The influence on the rates in general may dwindle in the order of structure > substituent > solvent.