Lanthanide induced paramagnetic shifts—derivation of equilibrium constants and absolute shifts in Eu(DPM)3 systems

Relationships between the magnitude of induced ¹H NMR shifts and the equilibrium conditions in solutions containing lanthanide shift reagents are discussed and applied to the shifts induced in several organic molecules by Eu(DPM)₃. Evidence that monoadduct formation is the predominant equilibrium in these solutions, and values of absolute shifts and equilibrium constants are reported. The results indicate that a contact mechanism makes the major contribution to the observed shifts in 4-methylpyridine. In the case of 2,4,6-trimethylpyridine the observed shifts are largely pseudocontact in origin.