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UBC Theses and Dissertations

An electron spin resonance study of nitrogen heterocyclic anions and ion pairs Paulus, Kurt Friedrich Gerhard


The purpose of this investigation has been to make a comparison of the experimental and theoretically calculated electron spin resonance spectra of nitrogen heterocyclic radical ions. Because of the recent nature of the field, and because of recent advances in theoretical aspects, the theory of ESR and of the calculation of spin density distributions is reviewed in some detail in Chapter I. In Chapter III the ESR spectra of methyl substituted pyrazine and pyridine anions prepared by chemical reduction with alkali metals are described. Huckel and McLachlan calculations have been performed using various theoretical models and it has been found that presently used simple theories of spin density distributions give a reasonably good explanation of the ESR spectra of these aromatic radical ions. The modified ESR spectra of the ion-pairs of methyl substituted pyrazine, pyridine, and benzene anions with alkali metal cations are examined in Chapter IV. Factors influencing the stability of the ion-pairs are discussed and the theory of alkali metal hyperfine interaction is considered in some detail. It is found likely that in future work attention will have to be directed at the estimation of the energy of excitation from the anion to the cation. Finally, the ESR spectra of some aromatic heterocyclic N-oxide anions generated electrolytically are examined in Chapter V and the results of Huckel and McLachlan calculations of the spin density distributions in the ions are discussed. Because of the perturbed nature of the molecules agreement with the experimental distributions is found to be not quite as satisfactory as with the pyrazine anions. The mechanism of the nitrogen hyperfine interaction in N-oxide anions is investigated and it is suggested that this interaction is overwhelmingly due to the spin density on the nitrogen itself. This last aspect of the ESR spectra of N-oxide anions awaits more complete experimental confirmation.

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