Natural Abundance 2H NMR for Liquid Crystal Studies. Application to 4‘-(Hexyloxy)-4-cyanobiphenyl

2H Natural-Abundance MAS NMR Spectroscopy: An Alternative Approach to Obtain1H Chemical Shifts in Solids

(2)H NMR was examined as an approach to determine (1)H chemical shifts in solids. For high-resolution observation, the line width due to (2)H quadrupole interaction and chemical-shift anisotropy was removed by magic-angle spinning and that due to (1)H-(2)H dipolar interactions by (1)H decoupling. Further, we showed that the sensitivity can be enhanced by applying (1)H to (2)H cross polarization and by adding spinning-sideband spectra. These make it possible to obtain (2)H natural-abundance MAS spectra revealing highly resolved (2)H signals. The second-order quadrupole effects of (2)H are also examined.

Indirect NMR detection in solids with multiple cross-polarization periods

The use of indirect detection for signal enhancement in solids is much less common than in liquids, but has attracted renewed interest recently. In this work we describe an indirect detection scheme that offers a large signal enhancement for rare spins in solids. The method uses multiple periods of cross polarization, each followed by an evolution period. The latter is increased stepwise in a pseudo 2D experiment, in which the signal of the rare spin is detected as modulation of the abundant spin. As an illustration of this method, the natural abundance deuterium NMR spectrum of a static powder sample of 1,2,4,5-tetramethylbenzene is presented.

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.