N.M.R. studies of dimethyl-acetylene and perfluorodimethylacetylene in nematic solvents

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Abstract
The high-resolution N.M.R. spectra of dimethyl-acetylene and perfluorodimethyl-acetylene have been observed in nematic phases. The effect of spinning the sample tube in the nematic range is examined. The indirect long-range HH and FF couplings are +2·7 and +2·2 hz. Structural information obtained, on the assumptions that the effects of nuclear vibrations and anisotropy in the indirect couplings are negligible, is compared with microwave and electron diffraction data, and the FCF angle is found to be 110.5° + 0.5° in contrast to earlier estimates of 107·5°. The anisotropy of the chemical shift for a CF bond in perfluorodimethyl-acetylene is about + 145 p.p.m.