Correlation 2D-NMR experiments involving both 13C and 2H isotopes in oriented media: methodological developments and analytical applications

Correlation 2D-NMR experiments for C-13 and H-2 isotopes turn out to be powerful methods for the assignment of the quadrupolar doublets in the H-2 NMR spectra of isotopically modified (polydeuterated or perdeuterated) or unmodified solutes in homogeneously oriented solvents, such as thermotropic systems or lyotropic liquid crystals. We review here the different pulse sequences, which have been employed, their properties, and their most salient applications. These 2D-NMR sequences have been used for (i) C-13-H-2 correlation with and without H-1 relay and (ii) H-2-H-2 correlation with C-13 relay. The C-13-H-2 correlation experiments without H-1 relay have been achieved for specifically deuterated or non-selectively deuterated analytes, but also more recently for isotopically unmodified ones thanks to the high sensitivity of very high-field NMR spectrometers (21.1T) equipped with cryogenic probes. The C-13-H-2 correlation 2D-NMR experiments are especially useful for the assignment of overcrowded deuterium spectra because the H-2 signals are correlated to C-13 signals, which benefit from a much larger dispersion of chemical shifts. In this contribution, particular attention will be paid to the use of correlation 2D-NMR experiments for H-2 and C-13 nuclei in weakly aligning, polypeptide oriented chiral solvents, because these methods are useful and original tools for enantiomeric and enantiotopic analyses. Copyright (c) 2014 John Wiley & Sons, Ltd.