High-Resolutjon nuclear-magnetic-resonance spectra of hydrocarbon groupings VI. The hydrogen spectra of carbon-13 substituted ethane, ethylene and acetylene

Abstract High-resolution spectra have been obtained from the hydrogen nuclei of appropriate isotopic mixtures of ethane, ethylene and acetylene containing one or two magnetic 13C nuclei. Analysis of these spectra has yielded the magnitudes of all but one of the possible inter - nuclear coupling constants in these molecules, including those between pairs of carbon nuclei. Where a given molecule has several coupling constants between pairs of the same type of nuclei the relative signs of these have also been determined. Discussion of the experimental results in terms of current theoretical treatments shows that in nearly all cases the contact, H3, term is the most important one in determining the magnitude of the coupling constants. Only in the case of the JCC and the long-range J'CH coupling constants of acetylene does it appear to be necessary to consider appreciable contributions from other terms.