Scalar coupling constants, in particular vicinal (3J) couplings, are widely used in NMR for the determination of relative stereochemistry and preferred conformation of molecules.A number of different empiric equations to correlate the dihedral angle with the 3J values have been proposed, the Karplus equation being the most famous.
The NOE (nuclear Overhauser effect) experiment is also extensively used, primarily, to define the stereochemistry within a molecule. Unlike scalar couplings, its mode of operation relies on the direct, through-space interaction between nuclei, and is independent of the presence of through-bond couplings.
The residual dipolar coupling (RDC) is able to provide global orientations between remote internuclear vectors. RDC have been widely used for the analysis of proteins and nucleic acids, but to a lesser extent in the small molecules area.More information