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The orientation of molecules with internal rotation in nematic phases

 

作者: LeonC. Ter Beek,   DanS. Zimmerman,   E. Elliott Burnell,  

 

期刊: Molecular Physics  (Taylor Available online 1993)
卷期: Volume 80, issue 1  

页码: 177-189

 

ISSN:0026-8976

 

年代: 1993

 

DOI:10.1080/00268979300102161

 

出版商: Taylor & Francis Group

 

数据来源: Taylor

 

摘要:

The anisotropic couplings obtained from the1H nuclear magnetic resonance (NMR) spectra of partially oriented molecules with internal rotation are difficult to analyse because the order parameters for each conformer cannot be deduced without assumptions. The purpose of this paper is to show how a model for the anisotropic short-range potential can be useful in the interpretation of the high-resolution1H NMR spectra of the flexible molecules furfural, 2-chlorobenzaldehyde, and 2,2′-dithiophene dissolved in a 55% Merck ZLI 1132-45%N-(p-ethoxybenzylidene)-2,6-dideutero-p'-n-butylaniline (w/w) mixture. In this nematic mixture there is no contribution to the anisotropic potential from the interaction between the solute molecular quadrupole moment and the average electric field gradient of the liquid crystal solvent; the dominant anisotropic intermolecular potential in this mixture is taken to result solely from short-range interactions. We find good agreement between experiment and the order parameters calculated by the model of short-range interactions. The ratios of order parameters for the s-cisand s-transconformers predicted by the model are used to calculate the statistical weights of the s-transconformation for the solutes: at 304 K,ptrans(furfural) = 0·45 ± 0·02,ptrans(2-chlorobenzaldehyde) = 0·901 ± 0·006 andptrans(2,2′-dithiophene) = 0·6094 ± 0·0008.

 

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