THE DIAZO GROUP AS AN EXAMPLE OF AN ISOLATED NUCLEAR-SPIN PAIR - N-15 ROTATIONAL RESONANCE

This solid-state nuclear magnetic resonance investigation is concerned with the N-15 spin pair present in the non-associated molecular solid, 5-methyl-2-diazobenzenesulphonic acid hydrochloride. The N-15 spectrum is investigated under both magic-angle and off-magic-angle conditions. For the magic-angle spinning case, when the isotropic shift difference of the two spins, or a submultiple thereof, precisely coincides with the frequency of sample rotation, spectral broadening is predicted. We observe unusually distinct and striking lineshape features for this compound under this rotational resonance condition from which we estimate a N-15-N-15 Separation of 1.110+/-0.004 Angstrom. A simplified description of the rotational resonance phenomenon is presented. The off-magic-angle spinning experiment allows us to deduce the relative orientations of the shielding tensors and the dipolar interaction. The experimental shielding parameters are compared with qualitative theoretical prediction.