text: CDAs are used with NMR spectroscopic analysis to determine enantiomeric excess and the absolute configuration of a substrate. Chiral discriminating agents are sometimes difficult to distinguish from chiral solvating agents (CSA) and some agents can be used as both. The speed of the exchange between the substrate and the metal center is the most important determining factor to differentiate between the use of a compound as a CDA or CSA. Generally, a CDA has a slow exchange whereas a CSA has a fast exchange. CDAs are more widely used than CSAs to determine absolute configurations because the covalent bonding to the substrate and auxiliary reagent produce species with greater conformational rigidity which creates greater differences in the NMR spectra. CDAs and CSAs can be used together to improve chiral recognition, although this is not a common.
  NMR shift reagents such as EuFOD, Pirkle's alcohol, and TRISPHAT take advantage of the formation of diastereomeric complexes between the shift reagent and the analytical sample.