15N 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 15N 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 15N 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 15N solid-state studies. The 15N 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. 1H-15N and 2H-15N distance measurements made by means of 1H detection are currently used in NMR crystallography. User friendly quantum chemical programs allow for the routine calculation of 15N chemical shielding and indirect spinspin coupling constants, especially using density functional theory (DFT). Applications of 15N 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.