¹⁴N quadrupolar, ¹⁴N and ¹⁵N chemical shift, and ¹⁴N^-1H dipolar tensors of sulfamic acid

A ¹⁴N solid-state NMR single crystal study was used to determine the ¹⁴N quadrupolar, chemical shift, and ¹⁴N^-1H dipolar tensors of sulfamic acid. The quadrupolar tensor is nearly axially symmetric, with the quasiunique axis aligned 3° away from the N-S bond. The quadrupole coupling constant of 0.794 MHz is substantially less than the gas-phase value (1.6682 MHz); ab initio calculations show that the difference can be attributed almost entirely to the significantly shorter N-S bond in the solid state. The single crystal study, together with ¹⁵N CP/MAS and CP/static experiments, yields an isotropic chemical shift that lies close to its solution value, and a chemical shielding anisotropy of about -80 ppm, and the dipolar couplings are about 10% smaller than computed from the neutron structure, probably because of vibrational averaging. All three tensors are almost collinear. HF, MP2, CI, and DFT(B3LYP) calculations of the nitrogen quadrupole coupling constant and shielding are also reported.