Definitions for "Chemical shift"
Keywords:  nmr, larmor, resonant, ppm, shift
The difference between the resonance frequencies of a given nucleus and a standard reference nucleus. It arises due to interactions of electrons with the applied magnetic field that generate local magnetic fields around atomic nuclei.
(delta - see Greek symbols) - the change in the Larmor frequency of a given nucleus when bound in different sites in a molecule, due to the magnetic shielding effects of the orbiting electrons. Chemical shifts make possible the differentiation of different molecular compounds and different sites within the molecules in high resolution NMR spectra. The amount of the shift is proportional to magnetic field strength and is usually specified in parts per million (ppm) of the resonance frequency relative to a standard.
a variation in the nominal Larmor frequency for a particular isotope within the imaging volume. The amount of shift introduced is directly proportional to the strength of the magnetic field, and is specified in parts per million (ppm) of the resonant frequency.