N-15 NMR spectroscopy in structural analysis

The implementation of both the directly and the inversely detected N-15 NMR techniques at the natural abundance level of the N-15 isotope is demonstrated for a diverse array of structural problems in organic chemistry. Following the application of N-15 NMR to the elucidation of the structures of natural compounds and synthetic products, the N-15-detected electron distribution in such molecules and following their reactions with other molecules and ions is discussed. A significant part of the N-15 structural analysis is devoted to the description of tautomers, rotamers, conformers, configurational isomers, and regioisomers. The changes in the N-15 parameters induced in structurally related compounds are described briefly. At present, the optimum probe-tube-sample configuration makes it possible to acquire inverse-detected H-1-N-15 correlation spectra on samples, where the total available sample is limited to amounts of < 1 mg (for molecules similar to <1000 Da and magnetic fields similar to > 400 MHz). N-15 NMR spectroscopy at the natural abundance level of N-15 nuclei has become a powerful tool which has substantially extended the analytical arsenal of organic chemists.