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Magnetic field induced dipolar couplings in the pretransitional region of a nematic liquid crystal

Magnetic field induced dipolar couplings in the pretransitional region of a nematic liquid crystal
Magnetic field induced dipolar couplings in the pretransitional region of a nematic liquid crystal
C-13 and H-1 NMR spectroscopy have been used to study the orientational order which develops when a nematogenic compound, 4-pentyl-4' -cyanobiphenyl (5CB), approaches the transition from the isotropic to the nematic phase at T-NI. The experiments yield values of field induced dipolar couplings, D-1(CHi)B, between all of the directly bonded carbon and hydrogen nuclei in the molecule, and 2D(HH)(B), the geminal dipolar coupling between protons in the first methylene group in the alkyl chain. The temperature dependence of these couplings shows that in each case they follow a divergence behavior governed by (T - T*)(-1),where T* is a temperature determined from the experimental data and which is close to but less than TNI. Experiments performed at spectrometer field strengths of 11.75 and 18.79 T confirm the prediction that the induced couplings should depend on the square of the applied field strength. It was found that, within experimental error, T* is the same for each field-induced coupling, and that T-NI - T* is the same at 11.75 and 18.79 T. It is shown that the set of field-induced couplings 1D(CHi)(B) obtained at a temperature close to T-NI can be used to derive a conformer distribution for 5CB in the isotropic phase.
behavior, resonance, molecules
1089-5639
5070-5078
Merlet, Denis
d2995516-205e-4bbb-b8e5-4aa521202eea
Lesage, Anne
bf3518dc-c688-4b8b-ab85-62ce2d6cbae0
Emsley, James W.
9d219d5e-28c0-4a8c-bf3d-1f78cd707c17
Merlet, Denis
d2995516-205e-4bbb-b8e5-4aa521202eea
Lesage, Anne
bf3518dc-c688-4b8b-ab85-62ce2d6cbae0
Emsley, James W.
9d219d5e-28c0-4a8c-bf3d-1f78cd707c17

Merlet, Denis, Lesage, Anne and Emsley, James W. (2005) Magnetic field induced dipolar couplings in the pretransitional region of a nematic liquid crystal. Journal of Physical Chemistry A, 109 (23), 5070-5078. (doi:10.1021/jp050665t).

Record type: Article

Abstract

C-13 and H-1 NMR spectroscopy have been used to study the orientational order which develops when a nematogenic compound, 4-pentyl-4' -cyanobiphenyl (5CB), approaches the transition from the isotropic to the nematic phase at T-NI. The experiments yield values of field induced dipolar couplings, D-1(CHi)B, between all of the directly bonded carbon and hydrogen nuclei in the molecule, and 2D(HH)(B), the geminal dipolar coupling between protons in the first methylene group in the alkyl chain. The temperature dependence of these couplings shows that in each case they follow a divergence behavior governed by (T - T*)(-1),where T* is a temperature determined from the experimental data and which is close to but less than TNI. Experiments performed at spectrometer field strengths of 11.75 and 18.79 T confirm the prediction that the induced couplings should depend on the square of the applied field strength. It was found that, within experimental error, T* is the same for each field-induced coupling, and that T-NI - T* is the same at 11.75 and 18.79 T. It is shown that the set of field-induced couplings 1D(CHi)(B) obtained at a temperature close to T-NI can be used to derive a conformer distribution for 5CB in the isotropic phase.

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More information

Published date: 16 June 2005
Keywords: behavior, resonance, molecules

Identifiers

Local EPrints ID: 20866
URI: http://eprints.soton.ac.uk/id/eprint/20866
ISSN: 1089-5639
PURE UUID: 2aacc331-5c84-4b7d-8024-6601d99b2a7a

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Date deposited: 02 Mar 2006
Last modified: 15 Jul 2019 19:25

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Contributors

Author: Denis Merlet
Author: Anne Lesage
Author: James W. Emsley

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