Paramagnetic nuclear magnetic resonance spectroscopy

[1][2] Although most NMR measurements are conducted on diamagnetic compounds, paramagnetic samples are also amenable to analysis and give rise to special effects indicated by a wide chemical shift range and broadened signals.

Paramagnetism diminishes the resolution of an NMR spectrum to the extent that coupling is rarely resolved.

For example, the broadening of signals is compensated in part by the wide chemical shift range (often 200 ppm in 1H NMR).

Directly bound nuclei have hyperfine shifts of thousands of ppm but are usually not oberservable due to extremely fast relaxation and line broadening.

[6] The effect of the contact term arises from transfer of unpaired spin density to the observed nucleus.

[2] The effect of the pseudocontact term arises from magnetic anisotropy of the paramagnetic center (reflected in g-anisotropy in the EPR spectrum).

This europium complex is used as an "NMR shift reagent" because its presence shifts the NMR signals for many organic compounds.
1 H NMR spectrum of 1,1'-dimethyl nickelocene , illustrating the dramatic chemical shifts observed in some paramagnetic compounds. The sharp signals near 0 ppm are from solvent.