A term used to characterize @[email protected] which have lifetimes of several minutes or greater in @[email protected] in @[email protected] solvents. Persistence is a kinetic or reactivity property. In contrast, radical @[email protected], which is a thermodynamic property, is expressed in terms of the C–H bond strength of the appropriate hydrocarbon. The @[email protected] of a radical is profoundly influenced by steric @[email protected] of the radical centre by bulky substituents.