The oxidations of cyclohexene (Ch) and tetralin (T) are induced by insertion of O-2 into their activated -C-H groups and primarily hydroperoxides, are formed. The onium salts promote the homolysis of the hydroperoxides formed. The efficiency of the catalysts depend on the polarizing power (partial charge) of the onium cations, the polarizability of the counteranions and the concentration of the catalyst. During the catalysed oxidation of substrates and during the catalysed decompositions of their hydroperoxides radical formation was detected by means of a spin trap, and some singlet O-2 was also evolved. The catalysed cooxidations demonstrated that the oxidation products mutually influence the transformations of these hydrocarbons. The onium-decavanadate ion-pair complexes are more effective catalysts than the pure onium salts. The Arrhenius parameters of the oxidations were determined and a possible mechanism is outlined. (C) 2003 Elsevier B.V. All rights reserved.