High resolution nuclear-magnetic-resonance spectra of hydrocarbon groupings

Abstract

The interpretation of ABC-type spectra is discussed in relation to several series of calculated spectra; some frequency and intensity sum rules are indicated. The hydrogen spectra of some vinyl derivatives, X. CH = CH₂ (X = F, Cl, Br, O and C) have been analysed. It is shown that and that a modified correlation holds between the J^gem coupling constants of CH₂ groups and the H-C-H angle in a range of molecules. All three coupling constants of the vinyl compounds decrease approximately linearly with the electronegativity of X; these effects are probably transmitted through the sigma bonds. By contrast the difference between the chemical shift of the = CH₂ group and that of the XHC = group is approximately linearly dependent on Taft's resonance parameter, σ_R , suggesting that the pi-electron distribution is principally concerned in this case.