Illustrated Glossary of Organic Chemistry

Magnetic induction: Magnetic field generation due to the presence of another magnetic field. In NMR spectroscopy, application of an external magnetic field B0 to a pi electron cloud causes these pi electrons to circulate. Because electrons bear an electric charge and are moving they create their own magnetic field. Depending upon their position within this induced magnetic field, nuclei may be deshielded (common) or shielded (uncommon).

Magnetic induction in a pi bond (viewed from the end). In the presence of B0 the pi electrons circulate, creating a magnetic field (shown in red). Where the vinyl protons are the lines of the induced magnetic field are parallel B0, so the magnetic field strength experienced by the vinyl protons is B0 plus the induced field. Compared to the case without the induced field, these vinyl protons are deshielded.