Multiple-pulse COSY NMR spectroscopy of oriented molecules in thermotropic cholesteric
Résumé
The coherent reduction of anisotropic NMR interactions in molecules oriented in a thermotropic cholesteric
phase, using a multiple-pulse COSY experiment, is described. The technique, which directly modifies the
spin part of the nuclear spin Hamiltonian, allows the transformation of second-order spectra into first-order
spectra. An experimental study of the evolution of the chemical shift and dipolar reduction factors is presented.
The effects of the finite pulse duration in the multiple-pulse sequence are discussed, and explicit equations
for the anisotropic interactions which take into account the pulse widths are obtained. The technique in
cholesteric solvents is illustrated by using two specific examples for AB and ABC type of spectra: 2,6-
dichloro-3-nitropyridine and 2-cyanofuran.