Extraction of 1H1H and 1H13C dipolar couplings from spectra acquired in inhomogeneous magnetic fields

Abstract

AbstractExperimental procedures are presented for the extraction of 1H1H and 1H13C dipolar couplings from molecules oriented in high magnetic fields without a requirement for high field homogeneity. These couplings impose restrictions on structure in a manner similar to NOE distances and can serve as useful additional constraints for defining structure. The experimental procedures involve pulse sequences which refocus the effects of magnetic field inhomogeneities but which retain dipolar couplings, scalar couplings and, in cases of chemically distinct groups, chemical shift differences. The methods are important for the extension of experiments to higher fields and more complex media where field homogeneity is hard to maintain. The experiments are illustrated using samples containing sodium acetate‐99% 13C2 or alanine‐99% 13C3 dissolved in a nematic liquid crystal and oriented in an inhomogeneous magnetic field. Coupling constants obtained from the studies are in good agreement with couplings extracted from one‐dimensional spectra obtained in homogeneous fields.