Effects of a Strong Electric Field on N.M.R. Spectra: The Absolute Sign of the Spin Coupling Constant

Abstract

High-resolution nuclear magnetic resonance spectra are dependent on two types of molecular constants, the shielding constant σA and the parameters JAX coupling the spins of nuclei A and X. This chapter provides an equation derived for the changes in the high-resolution nuclear magnetic resonance spectrum of a fluid subjected to a strong electric field E. The changes are proportional to E2 and are of three types: the field distorts the electronic structure of the molecules, there is a temperature-dependent orientation of the molecules, and the partial orientation of the molecules causes the magnetic dipole of nucleus X to produce a nonvanishing magnetic field at nucleus A. The measurements of the effects of a strong electric field on high-resolution nuclear resonance spectra could give the absolute signs of spin coupling constants J as well as the anisotropy in the shielding constant tensor σαB.Previouslytechniques were available for the determination of the relative signs of the coupling constants JAx and JAy in the molecule AXY; but no experimental method of obtainingabsolute signs has hitherto been available.