Fields
of Research, NMR of Oriented Molecules
Quadrupolar Interactions
Origin of Quadrupolar Interactions
Quadrupolar Interactions
Nuclei with spin I > 1/2 possess nuclear electric quadrupole moments.
The anisotropic orientational distribution of solute molecules in liquid
crystals makes it possible to use the NMR observables for the determination
of the quadrupole couplings for nuclei with spin >=1.
The Hamiltonian for a such partially aligned spin system contains an
extra term (see Theory of Liquid Crystal NMR Spectra).
For convenience we will write
qizz = eVizzQi/h
As in isotropic solutions, for anisotropic solutions the line broadening
effect will also appear, but in addition there may be a non-zero average value
of qizz, and this gives rise to extra lines in the spectrum.
In practice, for most quadrupolar nuclei splittings are not observed because
of rapid relaxations. Thus nuclei such as Iodine, Bromine and Chlorine, which
have large values of QCC do not give resolved high resolution NMR spectra in
liquid crystals.
Much smaller values of QCC occur for nuclei 10B, 11B,
14N and particularly 2H.
Return to "NMR of Oriented Molecules"
Last Update: April 22th, 1997
By: Alexan Shahatuni (msrc@moon.yerphi.am)