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Title: Measurement and assignment of long-range C-H dipolar couplings in liquid crystals by two-dimensional NMR spectroscopy

Abstract

We describe multidimensional NMR techniques to measure and assign {sup 13}C-{sup 1}H dipolar couplings in nematic liquid crystals with high resolution. In particular, dipolar couplings between aromatic and aliphatic sites are extracted, providing valuable information on the structural correlations between these two components of thermotropic liquid crystal molecules. The NMR techniques are demonstrated on 4-pentyl-4`-biphenylcarbonitrile (5CB), a well-characterized room-temperature nematic liquid crystal. Proton-detected local-field NMR spectroscopy is employed to obtain highly resolved C-H dipolar couplings that are separated according to the chemical shifts of the carbon sites. Each {sup 13}C cross section in the 2D spectra exhibits several doublet splittings, with the largest one resulting from the directly bonded C-H coupling. The smaller splittings originate from the long-range C-H dipolar couplings and can be assigned qualitatively by a chemical shift heteronuclear correlation (HETCOR) experiment. The HETCOR experiment incorporates a mixing period for proton spin diffusion to occur, so that maximal polarization transfer can be achieved between the unbonded {sup 13}C and {sup 1}H nuclei. To assign the long-range C-H couplings quantitatively. we combined these two techniques into a novel reduced-3D experiment, in which the {sup 1}H chemical shift-displaced C-H dipolar couplings are correlated with the {sup 13}C chemical shifts. 34more » refs., 6 figs., 2 tabs.« less

Authors:
;  [1];  [2]
  1. Lawrence Berkeley National Lab., CA (United States)
  2. BCH-Dorigny, Lausanne (Switzerland)
Publication Date:
OSTI Identifier:
380768
DOE Contract Number:  
AC03-76SF00098
Resource Type:
Journal Article
Journal Name:
Journal of Physical Chemistry
Additional Journal Information:
Journal Volume: 100; Journal Issue: 35; Other Information: PBD: 29 Aug 1996
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; LIQUID CRYSTALS; NMR SPECTRA; STRUCTURAL CHEMICAL ANALYSIS; CHEMICAL SHIFT; ORGANIC COMPOUNDS; MEASURING METHODS; COUPLING

Citation Formats

Hong, M, Pines, A, Univ. of California, Berkeley, CA, and Caldarelli, S. Measurement and assignment of long-range C-H dipolar couplings in liquid crystals by two-dimensional NMR spectroscopy. United States: N. p., 1996. Web. doi:10.1021/jp960972m.
Hong, M, Pines, A, Univ. of California, Berkeley, CA, & Caldarelli, S. Measurement and assignment of long-range C-H dipolar couplings in liquid crystals by two-dimensional NMR spectroscopy. United States. https://doi.org/10.1021/jp960972m
Hong, M, Pines, A, Univ. of California, Berkeley, CA, and Caldarelli, S. 1996. "Measurement and assignment of long-range C-H dipolar couplings in liquid crystals by two-dimensional NMR spectroscopy". United States. https://doi.org/10.1021/jp960972m.
@article{osti_380768,
title = {Measurement and assignment of long-range C-H dipolar couplings in liquid crystals by two-dimensional NMR spectroscopy},
author = {Hong, M and Pines, A and Univ. of California, Berkeley, CA and Caldarelli, S},
abstractNote = {We describe multidimensional NMR techniques to measure and assign {sup 13}C-{sup 1}H dipolar couplings in nematic liquid crystals with high resolution. In particular, dipolar couplings between aromatic and aliphatic sites are extracted, providing valuable information on the structural correlations between these two components of thermotropic liquid crystal molecules. The NMR techniques are demonstrated on 4-pentyl-4`-biphenylcarbonitrile (5CB), a well-characterized room-temperature nematic liquid crystal. Proton-detected local-field NMR spectroscopy is employed to obtain highly resolved C-H dipolar couplings that are separated according to the chemical shifts of the carbon sites. Each {sup 13}C cross section in the 2D spectra exhibits several doublet splittings, with the largest one resulting from the directly bonded C-H coupling. The smaller splittings originate from the long-range C-H dipolar couplings and can be assigned qualitatively by a chemical shift heteronuclear correlation (HETCOR) experiment. The HETCOR experiment incorporates a mixing period for proton spin diffusion to occur, so that maximal polarization transfer can be achieved between the unbonded {sup 13}C and {sup 1}H nuclei. To assign the long-range C-H couplings quantitatively. we combined these two techniques into a novel reduced-3D experiment, in which the {sup 1}H chemical shift-displaced C-H dipolar couplings are correlated with the {sup 13}C chemical shifts. 34 refs., 6 figs., 2 tabs.},
doi = {10.1021/jp960972m},
url = {https://www.osti.gov/biblio/380768}, journal = {Journal of Physical Chemistry},
number = 35,
volume = 100,
place = {United States},
year = {Thu Aug 29 00:00:00 EDT 1996},
month = {Thu Aug 29 00:00:00 EDT 1996}
}