Long-Range Nuclear Magnetic Shielding in Molecules and the Anisotropy in the Magnetic Susceptibility of a Carbon-Carbon Single Bond

Abstract

A method is discussed for obtaining quantitative measurements of long-range NMR shielding effects in molecules based on the theory of Ramsey as extended by McConnell. These effects are shown to arise principally from the diamagnetic part of the magnetic susceptibility of the individual bonds when the origin of coordinates is taken at the geometric center of the bond. Application is made to saturated hydrocarbon alcohols for which the only long-range shielding contributions come from tetrahedral carbon-carbon bonds. From high-resolution NMR measurements of tertiary protons on carbocyclic molecules the existence of these effects is verified and the magnitude of the magnetic anisotropy on the individual bonds causing such effects is determined.