AN APPLICATION OF SOME ELECTRON DENSITY, ELECTRIC DIPOLE, AND MAGNETIC DIPOLE MODELS TO THE GAS PHASE PROTON SHIFTS OF SOME SUBSTITUTED ETHYLENES

Abstract

Measurements in the gas phase of the proton shifts relative to ethylene of methyl vinyl ether, of vinyl chloride, and of the three dichloroethylenes are reported. It is suggested that available molecular orbital calculations somewhat overestimate delocalization in the chloroethylenes. If this is so, then a model involving electrostatic fields arising from excess π-electron densities and from electric dipoles originating from the substituents, as well as magnetic fields from a point dipole representing the anisotropy of the substituents, predicts shifts in reasonable agreement with experiment for β-protons. The agreement for α-protons is not as good. The gas phase measurements are compared to measurements in the inert solvents, tetramethyl-silane or cyclohexane.