Electron-nuclei hyperfine interactions in imino nitroxide radicals

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Abstract
The 1H and 13C N.M.R. spectra of a series of imino nitroxide radicals have been studied to obtain electron-nuclei hyperfine coupling constants. A comparison of the spin distribution in these radicals with that previously determined for a series of nitronyl nitroxide radicals indicates a similar mechanism of spin propagation from the heterocyclic ring to the aryl ring, in accord with theoretical predictions [1]. The methyl protons on the two sides of the imino nitroxide ring are found to have different coupling constants: these are discussed in terms of separate interactions with spin at the nitrogen and oxygen atoms. N.M.R. lines are observed from all of the aryl 13C atoms and from the α and β carbon atoms of the heterocyclic ring. The aromatic carbon spin polarization parameters are found to be in accord with those previously reported [2]. Polarization of the bridgehead-ortho bond by spin in the heterocyclic ring appears to contribute to the coupling constants of the ortho carbon atoms.