The Chemical Shift

Abstract

The chemical shift (as defined by IUPAC) in terms of measured frequencies1{\$}{\$}{\backslash}delta = {\backslash}left( {\{}{\backslash}nu - {\backslash}nu {\_}{\{}{\{}{\backslash}text{\{}ref{\}}{\}}{\}} {\}} {\backslash}right){\{}{\backslash}text{\{}/{\}}{\}}{\backslash}nu {\_}{\{}{\{}{\backslash}text{\{}ref{\}}{\}}{\}}{\$}{\$}is related to a fundamental molecular property, the nuclear magnetic shielding, $σ$. For a molecule held in a fixed orientation in a uniform magnetic field B, the field at a selected point in the vicinity of the molecule is different from B because of the small field arising from the circulations of the electrons induced by the magnetic field*:2{\$}{\$}B{\_}{\{}{\{}{\backslash}text{\{}local{\}}{\}}{\}} {\{}{\backslash}text{\{} = {\}}{\}}{\backslash}left( {\{}1 - {\backslash}sigma {\}} {\backslash}right)B{\$}{\$}