The enthalpies of formation for fifteen alpha-hydroxyliydroperoxides and alpha-hydroxyperoxyl radicals with various structures were calculated. Using the crossing parabolas method, experimental data on the degradation of alpha-hydroxyperoxyl radicals were analyzed and the kinetic parameters that characterize these reactions were calculated. The activation energies of the degradation rate constants of fifteen alpha-hydroxyperoxyl radicals were calculated from these parameters. The enthalpies of degradation for six alpha-hydroxyperoxyl radicals of polyhydric alcohols and the enthalpies of their formation were calculated using the experimental data. The rate constants of the backward reaction, namely, hydroperoxyl radical addition to a number (21) of carbonyl compounds, and the enthalpies and Gibbs energies for H2O2 addition to some aldehydes and ketones to form alpha-hydroxyhydroperoxides were calculated. The kinetic characteristics of the degradation of alpha-hydroxyperoxyl radicals are compared to those of other reactions of intramolecular hydrogen-atom transfer in oxygen-centered radicals. An important role of low triplet repulsion in these reactions, which ensures their fast rate, was noted.