Within the framework of a parabolic model of reactions of radical detachment, the activation energies and rate constants of reactions of hydrogen atom detachment from the C-H bond of forty three hydrocarbons of different structure have been calculated. In calculations, use was made of a kinetic parameter calculated from experimental data concerning reactions of NO3 with hydrocarbons. The contribution of the reaction of NO2 with RH to overall initiation during the oxidation of hydrocarbons is discussed.