Three bond coupling constants are particularly useful for determining stereochemistry as the Karplus relationship relates them to torsion angles. Typically, however, only a qualitative analysis to define rotamers is used, as measuring the couplings accurately is not easy. Homonuclear 3JHH couplings are normally obtained from 1D 1H spectra, and are fairly straightforward to measure, but heteronuclear 3JCH couplings are more difficult to obtain. There are a variety of methods available for measuring long range heteronuclear couplings, each with their own advantages and disadvantages. Three of them, that have been implemented at the Skaggs NMR Facility, will be described below.
