Quadrupolar coupling

From NMR Wiki

Quadrupolar coupling is an interaction that occurs in nucleus that has more than 2 different spin states. Only nuclei with spin 0 or 1/2 do not have this interaction. On one hand this interaction is source of addtional information, but on the other hand it could make the signal decrease too fast to be observed (as it is for ¹⁴N). This interaction exists even without any applied magnetic field, where the energy of corresponding splitting (even in the absence of external field) between the different states could be quite strong (several hundreds of kHz, to some MHz). This splitting is what is detected by nuclear quadrupolar resonance (NQR).

Contents 1 Source of this interaction 2 Consequence of the interaction 3 Strength of this interaction 4 Usage of this interaction 5 References

Source of this interaction

Nucleus for spin equal or higher than 1 have an energy splitting that happens when their is an electric field gradient on the nucleus. So highly symmetric molecules will not have this electric field, and so their will not be this energy splitting. The electric field depend on the geometry of the molecule. The splitting that appear because of this interaction could allow to determine the relative orientation.

Consequence of the interaction

The rapid change caused by the fluctuation of the electric field could lead to fast relaxation, this occures slow enough to be observed for deuterium nucleus. But in the the case of 14N that is much more strongly coupled to the local electric field gradient, the relaxation is too fast to be observed. Even nearby nucleus relax faster due to the Scalar coupling to this very fast relaxing nucleus.

Strength of this interaction

Usage of this interaction

• determination the orientation of methyl groups using deuterium NMR in solid state.
• determination of dynamics using the fast relaxation of deuterium in solution for macromolecules
• determining the binding of water (²³Na or ²H)

References

[1]