Chapter 5: ¹⁴N Solid-state NMR Check Access

Nitrogen is commonly found in organic, inorganic and biological solids, yet is extremely challenging to study by solid-state NMR. This chapter presents an overview of modern methods for observing the almost-100% naturally abundant ¹⁴N isotope, a spin-1 nucleus typically subject to a large quadrupolar interaction. Either the fundamental (Δm=1) or overtone (Δm=2) ¹⁴N transitions can be observed, and these two options require very distinct experimental approaches. The former transitions are usually broadened over several MHz and require frequency-swept pulses and piecewise acquisition, while the latter transition gives far narrower linewidths and higher spectral resolution, but exhibits some unusual spin physics, particularly under magic-angle spinning. The possibility of sensitivity enhancement by polarisation transfer, or by the indirect detection of ¹⁴N signals using more amenable nuclei, is also discussed.