THE DIAZO GROUP AS AN EXAMPLE OF AN ISOLATED N-15-N-14 NUCLEAR-SPIN PAIR - A STATIC AND VARIABLE SPINNING FREQUENCY INVESTIGATION

The N-15-N-14 heteronuclear spin pair present in the polycrystalline compound 5-methyl-2-diazobenzenesulphonic acid hydrochloride singly labelled with N-15 at either the alpha- or the beta-position is investigated by solid-state nuclear magnetic resonance. The N-15 spectrum is obtained both under static and spinning conditions. Unusually well resolved fine structure is observed in both cases and, in particular, the static spectra allow a direct and straightforward measurement of the N-15-N-14 internuclear dipolar coupling in addition to values of the principal components of the shielding tensors for N-15 labelling (at either the alpha- or the Beta-positions of the diazo moiety) and their orientation relative to a molecular frame. We also present a preliminary theoretical discussion concerning the origin of the observed spinning frequency dependence of the sideband fine structure.