14N and 2H quadrupole double resonance in salts of cytosine and adenine

Abstract

¹⁴ N and ²H quadrupole resonance frequencies have been measured at room temperature by double resonance techniques in four salts of cytosine and the dihydrobromide of adenine. By means of careful Zeeman measurements, consistent quadrupole coupling constants and asymmetry parameters have been deduced and assigned to specific nuclei in the molecule. The approximate orientation of the ¹⁴N electric field gradient tensor has been deduced by a comparison of the results with those for solid imidazole discussed in the previous paper. Protonation of the cytosine molecule is shown to increase the 2p_π conjugation of the exocyclic NH₂ group with the ring, so that much of the positive charge of the cation may reside on the amino group.