title: Measurement of Large Dipolar Couplings of a Liquid Crystal with Terminal Phenyl Rings and Estimation of the Order Parameters.
abstract: NMR spectroscopy is a powerful means of studying liquid-crystalline systems at atomic resolutions. Of the many parameters that can provide information on the dynamics and order of the systems, (1) H-(13) C dipolar couplings are an important means of obtaining such information. Depending on the details of the molecular structure and the magnitude of the order parameters, the dipolar couplings can vary over a wide range of values. Thus the method employed to estimate the dipolar couplings should be capable of estimating both large and small dipolar couplings at the same time. For this purpose, we consider here a two-dimensional NMR experiment that works similar to the insensitive nuclei enhanced by polarization transfer (INEPT) experiment in solution. With the incorporation of a modification proposed earlier for experiments with low radio frequency power, the scheme is observed to enable a wide range of dipolar couplings to be estimated at the same time. We utilized this approach to obtain dipolar couplings in a liquid crystal with phenyl rings attached to either end of the molecule, and estimated its local order parameters.
authors.affiliation: NMR Research Centre, Indian Institute of Science, Bangalore 560012 (India).|Department of Physics, Indian Institute of Science, Bangalore 560012 (India).
authors.forename: R V Sudheer
authors.initials: RV
authors.lastname: Kumar
authors.affiliation: NMR Research Centre, Indian Institute of Science, Bangalore 560012 (India). kvr.nmr@gmail.com.
authors.forename: Krishna V
authors.initials: KV
authors.lastname: Ramanathan
keywords: NMR spectroscopy; heteronuclear dipolar couplings; liquid crystals; local field spectroscopy; order parameters