77Se NMR Spectroscopy and Its Applications in Chemistry

Selenium (77Se) has attracted the widest nuclear magnetic resonance (NMR) spectroscopic interest among the group 16 elements. The most important 77Se NMR parameter is the chemical shift reflecting the chemical environment around the selenium atom. Chemical shift tensors can be obtained from the rotational side-band pattern in solid-state 77Se NMR spectra and offer more detailed information. Conformational analysis of selenium-containing compounds by temperature-variable NMR spectroscopy (DNMR) is facilitated by the great sensitivity of the 77Se chemical shift. Generally, chemical shift differences of selenium atoms in different conformers (at low temperatures) are much larger than those of carbon or hydrogen atoms. Therefore, the coalescence temperature in 77Se NMR spectra is higher than in 1H or 13C NMR experiments of the same compounds. The 77Se NMR chemical shift tensors of a selection of inorganic and organic selenium-containing compounds have been obtained from solid-state NMR, partly involving cross-polarization (CP) and magic angle spinning (MAS). 77Se NMR spectroscopy is recognized as a useful tool for the elucidation of molecular structures of selenium-containing compounds and intermediates. In other applications, 77Se nuclei are used as probes for detecting molecular chirality, intramolecular interactions, or bond situations. In addition, some methods have been invented where selenium-containing auxiliaries are applied to selenium-free compounds.