Available experimental data on the rate constants of reactions of nitroxyl radicals with phenols, aromatic amines and thiophenols have been analysed within the framework of a parabolic model of the transient state, and the parameters characterizing the reactivity of compounds of each of these groups have been calculated. As regards the activation energy of the thermoneutral reaction E-e0, these inhibitors break down in the following sequence (E-e0, J/mole): aromatic amines (38.3), phenols (45.8), hydroxylamines (45.8), thiophenols (49.3), sterically hindered phenols (52.5). These parameters have been used to calculate the activation energies and rate constants for 150 reactions with the participation of nitroxyl radicals.