NMR of liquid crystals

Abstract

The analysis of NMR spectra of molecules in the liquid crystal phase gives rise to information that can be used to determine molecular structure and internal flexibility. The information extracted, the dipolar couplings, are directly related to the separation between atomic pairs averaged over the entire motion of the molecules in the liquid crystal phase. The dipolar couplings are modelled using the Additive Potential model, which yields the order parameters and the potential barriers for rotation within flexible molecules.

Traditionally, due to the complexity of these spectra, studies have been restricted to small molecules dissolved in liquid crystal solvents, often with simplified spin systems from chemical substitution. The analysis of phenyl benzoate is an example of this type of work and is presented here. In order to advance beyond these limitations, the possibilities of Variable Angle Sample Spinning combined with ¹³C-{¹H} NMR spectroscopy are explored. Early work concentrates on the analysis of fluorobenzene and 2,2'-difluorobiphenyl dissolved in nematic liquid crystal solvents. VASS has proved to be a powerful tool which has allowed the analysis of NMR spectra to be simplified and has demonstrated that spectra taken near the magic angle can be used to determine the absolute signs of the scalar couplings simply. Different decoupling schemes are also investigated and compared to further optimise the procedure being developed. Finally, the NMR spectra of the liquid crystals I35 and I52 in the liquid crystal phase were successfully analysed combining all the preceding techniques, and the internal motion of the molecules successfully modelled.

More information

Identifiers

Catalogue record

Export record

ASCII CitationAtomBibTeXData Cite XMLDublin CoreDublin CoreEP3 XMLEndNoteHTML CitationHTML CitationHTML ListJSONMETSMODSMPEG-21 DIDLOpenURL ContextObjectOpenURL ContextObject in SpanRDF+N-TriplesRDF+N3RDF+XMLRIOXX2 XMLReferReference ManagerSimple Metadata