Illustrated Glossary of Organic Chemistry

Chemical shift (δ): The position of a signal along the x-axis of an NMR spectrum. More precisely, the difference between the frequency of photon required for nuclear spin flip of the nucleus in question and nuclear spin flip of a reference molecule -- sometimes tetramethylsilane (TMS) or CDCl3 -- divided by the operating frequency of the NMR spectrometer. (Equation given below.) Not to be confused with δ+ or δ-, symbols used to indicate partial charge.