residual chemical shift anisotropy residual chemical shift anisotropy residual chemical shift anisotropy (rcsa) is the difference between the chemical shift anisotropy (csa) of aligned and non-aligned molecules. it is normally three orders of magnitude smaller than the static csa, with values on the order of parts-per-billion (ppb). rcsa is useful for structural determination and it is among the new developments in nmr spectroscopy.