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K V Ramanathan

Publications and source records attributed to K V Ramanathan.

5 recordsLinked to original sources
PubMed2004

Assignment of 13C resonances of a nematic liquid crystal using off-magic angle spinning.

A novel method for assigning the resonances in the 13C NMR spectrum of a static liquid crystalline sample in its nematic phase is proposed. The method is based on the fact that the carbon chemical shifts in the isotropic phase and in the oriented phase under static and off-magic angle spinning (OMAS) conditions are uniquely related by the tensorial property of the CSA tensor, requiring just one OMAS spectrum and the assignment in the isotropic phase. A computational procedure is proposed to take into account deviations arising out of non-ideal experimental conditions and the assignments are made by identifying the minimum in the differences in the frequencies between calculated and experimental line positions. Practical implementation of the method has also been demonstrated in the case of the liquid crystal N-(4-ethoxybenzylidene)-4-n-butylaniline.

Algorithms↗
PubMed2002

Cross-polarization from the dipolar reservoir under the mismatched Hartmann-Hahn condition.

Cross-polarization from the dipolar reservoir for a range of mismatched Hartmann-Hahn conditions has been considered. Experiment, in general, agrees with the dispersive Lorentzian behavior expected on the basis of quasi-equilibrium theory. It is observed that inclusion of additional mechanisms of polarization transfer lead to an improvement of the fit of the experimental results. The utility of extending the technique to the case of ordered long chain molecules, such as liquid crystals, for the measurement of the local dipolar field is also presented.

Journal Article↗
PubMed1998

Off-resonance effects in two-dimensional NQR spectroscopy using a single crystal.

Two-dimensional nutation pure NQR experiments on 35Cl have been carried out on a single crystal of NaClO3. The 2D nutation experiment separates out different orientations of each chemically equivalent site in a unit cell as a separate frequency in the omega1 domain. The squares of the observed frequencies lie on a straight line with respect to the squares of the offsets, confirming the expected offset dependence quantitatively. The intercepts at zero offset yield the relative orientations of the efg tensors with respect to the axis of the radiofrequency coil.

Crystallization↗
PubMed1998

Natural abundance 2H NMR spectra of molecules oriented in liquid crystals.

It has been demonstrated that the natural abundance 2H NMR spectra of molecules dissolved in liquid crystals can be obtained easily with the help of present-day high-resolution FT NMR spectrometers. Such spectra obtained in the case of benzene and chloroform dissolved in liquid crystals are reported. These experiments could serve as valuable aids for the analysis of the complex proton NMR spectra of oriented molecules.

Benzene↗