Assigning stereochemistry with NOEs

Relative stereochemistry can often be determined by analysis of nuclear Overhauser effects or NOEs. I have seen many papers where the stereochemistry was defined based on the observation of one particular peak, but this may not be sufficient and some care must be taken when interpreting NOEs. Here I offer a few pointers on how best to interpret the crosspeaks in NOESY and ROESY spectra.

Residual chemical shift anisotropy

Residual chemical shift anisotropy (RCSA) is another parameter that is being incorporated into the structure elucidation toolbox. As its name suggests, RCSA is similar to residual dipolar coupling (RDC) in that it requires partial alignment of the sample so that differences between the aligned and unaligned states can be measured.

Homodecoupling

Homodecoupling is a technique for selectively removing coupling in 1D NMR spectra. Often 1D ¹H spectra show complex splitting patterns that are difficult to interpret. Selectively eliminating one coupling may allow a multiplet to be interpreted or enable measurement of couplings that could not otherwise be quantified. Recently, we used homodecoupling to assign the stereochemistry of a pair of enantiomers.