Nuclear Magnetic Resonance Study of Tetrafluoro-1,3,-Dithietane in an Isotropic and a Lyotropic Liquid Crystalline Medium

Abstract

Fluorine magnetic resonance experiments on tetrafluoro‐1,3‐dithietane (F₄C₂S₂) in a lyotropic mesophase show conclusively that the molecule possesses $D_{\text{2h}}$ symmetry. Analysis of ¹⁹F spectra in the nematic mesophase over a range of temperatures from 299–321°K indicate that the anisotropic contribution to the spin–spin coupling constant is negligible. From the observed spectra it is impossible to determine all bond distances. However, assuming a C–F distance of 1.334 Å and a C–C distance of 2.413 Å, an FCF angle of 109.2° ± 0.5 can be calculated. In addition, high‐resolution spectra have been obtained for both the ¹³C nuclei and ¹³C–F satellites in the isotropic phase. The geminal F–F coupling is found to be +137.06 Hz. Although the ¹³C and ¹³C–F satellite spectra in isotropic media are insensitive to permutation of the cis and trans F–F couplings, the nematic phase results permit the unambiguous assignment of the smaller coupling to the cis arrangement. The variation of the motional constants with temperature, the determination of the absolute signs of spin–spin coupling constants, and anisotropy in the chemical shift are discussed.