Linear Variation of Proton Magnetic Shielding with Electric Field

Abstract

The linear variation of nuclear magnetic shielding with electric field is calculated semiquantitatively by a variation method and by a perturbation method. The effect is sufficiently large to be significant for protons in molecules containing polar groups or in ions, as these protons experience intramolecular electric fields of ∼10⁶ statV/cm. The effect on protons in solids for laboratory electric fields would only be a fraction of the (magnetic) dipolar linewidth and is therefore not observable. The calculation gives good agreement with the several experimental values from the literature. The intramolecular (electric) dipolar field is then used to explain the low‐field shift in resonance frequency of the methylene protons in in ethyl alcohol—an important example of the chemical ``inductive effect.''