NMR studies of spherical molecules dissolved in smectic liquid crystal solvents

Abstract

The proton NMR spectra of the nearly tetrahedral molecules CH 3CCl 3 and CH 3SiCl 3 and the tetrahedral molecules (CH 3) 4Si and (CH 3) 4C in smectic liquid crystal solvents are discussed. The relatively large magnitudes observed for the orientation parameter S zz in the smectic phase enable the 1H chemical shielding anisotropies of CH 3CCl 3 and CH 3SiCl 3 to be obtained with good accuracy. In addition, it was also observed that the intramolecular direct dipole-dipole interaction did not vanish for the spherical (CH 3) 4Si and (CH 3) 4C systems. A splitting is observed in the 1H spectra for these molecules which is an order of magnitude larger than previous values obtained using nematic liquid crystal solvents. Values of the direct dipole-dipole coupling constant D HH, and orientation parameter S zz for the two molecules are reported, as well as D 13 CH for (CH 3) 4Si.