NMR studies of C-13-iodomethane: Different behavior in thermotropic and lyotropic liquid crystals

High-resolution NMR spectra of C-13-iodomethane dissolved in thermotropic and lyotropic liquid crystalline solvents have been used to measure H-1-H-1 and C-13-H-1 dipolar couplings. The ratio of these two couplings, which is a function of the H-C-H bond angle in C-13-iodomethane, is, in general, different from that expected from the known molecular structure; solvent-solute interactions in liquid crystalline solutions are responsible for this difference. In thermotropic liquid crystalline solutions, the apparent bond angle deviation (Deltatheta(a)) increases with decreasing molecular ordering. In contrast, in lyotropic liquid crystals, no significant spectral aberration has been observed. These results indicate a fundamental physicochemical difference between the intermolecular interactions that prevail in thermotropic and lyotropic liquid crystals.