Charge density and NMR parameters. Aliphatic derivatives

The charge distribution in several substituted aliphatic derivatives was determined by a parametric MOLCAO method. The charges were successfully employed to interpret NMR parameters, namely proton and carbon chemical shift and vicinal proton-proton coupling constants in ethyl derivatives and carbon-proton coupling constants.The linear correlations found between NMR parameters and charge densities are restricted to substituents of the same row of the periodic system. The decay along the aliphatic chain of the perturbation induced by substituents on proton chemical shift is also reproduced by charge distribution. Some results also seem to indicate that the substituents affect the hybridization of the attached carbon atom.