Aminoxyl (R2N-O-center dot), amidoxyl (RCO-N(O-center dot)-R) and imidoxyl ((RCO)(2)N-O center dot) radicals play a key role in the aerobic oxidation catalyzed by N-hydroxyderivatives. The rationalization of the mechanisms of a variety of oxidations is based on thermochemical, kinetic and spectroscopic investigations and on solvent effects and it has suggested new selective synthetic developments. In collaboration with CIBA Speciality Chemicals a new catalytic system resulting from the combination of a persistent macrocyclic aminoxyl radical and the couple Mn(NO3)(2)/Co(NO3)(2) has been developed: it is particularly effective for the aerobic oxidation of alcohols to aldehydes and ketones under mild conditions (air at room temperature and atmospheric pressure); above all it presents the great advantage of an easy recovery and recycling providing the possibility of practical applications. The kinetic iinvestigation of the substituent effect in the oxidation of benzyl alcohols has allowed identifying the rate-determining step of the oxidation. The amidoxyl radicals, generated "in situ" from N-hydroxyamide, revealed particularly effective catalysts for the aerobic peroxidation of polyunsaturated fatty acids and esters, which is involved in the origin of several important pathologies, such as tumor initiation and atherosclerosis. The kinetic investigation has contributed to explain the mechanism of the oxidation and to develop the most effective methodology for the synthesis of hydroperoxides. The importance of enthalpic, polar, captodative, solvent effects and "molecule-induced homolysis" has been emphasized in the oxidation. halogenation and acetoxylation of a variety of classes of organic compounds (hydrocarbons, alcohols, aldehydes, amines. ainides. silanes) by O-2 and N-hydroxyimide catalysis. The high selectivity often observed and the very mild experimental conditions, based on the mechanistic interpretation, provide industrial potentiality to the catalytic processes. (c) 2006 Elsevier B.V. All rights reserved.