Nitrogen NMR Spectroscopy

Abstract

Publisher Summary Nitrogen nuclear magnetic resonance (NMR) is finding new applications. This chapter presents some of the applications of the nitrogen NMR. The element nitrogen in its natural occurrence has two isotopes; 14N and 15N. The nuclei of both possess magnetic moments; consequently, both give nuclear magnetic resonance (NMR) spectra and additionally may affect the spectra of other nuclei. The NMR spectra of nitrogen nuclei may provide an important contribution to the development of the general theory of chemical shifts, by allowing a rigorous check of current theories. This arises from the variety of nitrogen valence states occurring in the molecules, including more or less non-bonding electron pairs, many types of bonds of varying polarity and hydrogen bonding, as well as the common occurrence of nitrogen atoms in both neutral and ionic species. 14N nucleus has an electric quadrupole moment and this is responsible for producing broad-line NMR spectra. Broad lines often occur both in the spectrum of the 14N nucleus and in the spectrum of any nucleus spin coupled to the nitrogen nucleus that may preclude the detection of any spin-spin coupling between these nuclei. The electric quadrupole relaxation process of the 14N nucleus may influence the NMR spectra of nuclei that are spin-coupled to it. The most frequently encountered example is the N-H coupling. The chapter presents some examples of nitrogen chemical shifts in the organic and inorganic molecules. However, spin-spin coupling, involving nitrogen nuclei, is readily observed for the 15N isotope than for 14N. As 15N nuclei possess a spin of 1/2 and no quadrupole moment, these give NMR spectral patterns similar to those arising from lH and 19F interactions.