N-15 NMR Spectroscopy in structural analysis: An update (2001-2005)

Since our previous review article (Curr. Org. Chem. 2002, 6, 35), significant improvements and an array of N-15 NMR applications in structural analysis have been published. This report aims to update coverage of improvements in methodology and various types of applications published over the period 2001-2005. Substantial progress in cryogenic probe technology and the commercial availability of cryoprobes have facilitated the measurement of N-15 NMR parameters. The number of solid-state applications has increased significantly during the past few years. In contrast to our previous review, this article covers N-15 solid-state studies. The N-15 NMR chemical shifts of organic molecules are routinely measured by using cross-polarization magic-angle spinning (CP/MAS) techniques. The principal values of the chemical shift tensors can also be determined. H-1-N-15 and H-2-N-15 distance measurements made by means of H-1 detection are currently used in NMR crystallography. User friendly quantum chemical programs allow for the routine calculation of N-15 chemical shielding and indirect spin-spin coupling constants, especially using density functional theory (DFT). Applications of N-15 NMR spectroscopy in various fields of chemistry are summarized here. Major sections represent tautomerism, complexation, protonation, and hydrogen bonding. The other topics comprise N-alkylation, N-oxidation, regioisomerism, and changes in configuration or conformation.