Calculations of magnetic resonance parameters for the protonated nitroxide radical

Electron and magnetic resonance parameters of the protonated H₂NO radical have been calculated by the INDO and CNDO/SP methods for different models. Calculated changes of magnetic resonance parameters on protonation are consistent with experiment. The most appropriate structure has been found to be one in which the proton is in the plane of the radical with r(O?.H⁺) = 1.05 A.Calculated signns of the proton spin density for the models concerned are opposite to those of the spin density on the proton of a ligand involved in the hydrogen bonding for analogous models of hydrogen bond systems formed by the nitroxide radical.In the case of the protonated radical, taking into account the interaction with a solvent molecule leads to more reasonable results for large O?.H⁺ distances.