15N NMR Spectroscopy in Structural Analysis

The implementation of both the directly and the inversely detected 15N NMR techniques at the natural abundance level of the 15N isotope is demonstrated for a diverse array of structural problems in organic chemistry. Following the application of 15N NMR to the elucidation of the structures of natural compounds and synthetic products, the 15N-detected electron distribution in such molecules and following their reactions with other molecules and ions is discussed. A significant part of the 15N structural analysis is devoted to the description of tautomers, rotamers, conformers, configurational isomers, and regioisomers. The changes in the 15N parameters induced in structurally related compounds are described briefly. At present, the optimum probe-tube-sample configuration makes it possible to acquire inverse-detected 1H-15N correlation spectra on samples, where the total available sample is limited to amounts of < 1 mg (for molecules [sim] 400 MHz). 15N NMR spectroscopy at the natural abundance level of 15N nuclei has become a powerful tool which has substantially extended the analytical arsenal of organic chemists.