Diamagnetische afscherming van kernen: Lokale diamagnetische stroom

In a molecule, an applied magnetic field, B₀, causes the electron density surrounding the nuclei to circulate, setting up a local diamagnetic current, which induces a local magnetic field, B_local, opposing B₀.

So, the effective magnetic field experienced by these nuclei, B_effective, equals B₀ minus B_local, in a phenomenon called local diamagnetic shielding.

Essentially, B_local increases with the electron density surrounding the nuclei, leading to increased shielding and lower B_effective.

Since electron densities vary within a molecule, each nucleus is shielded to a different extent and experiences a different effective field.

A nucleus in an electron-dense environment is well-shielded from the applied magnetic field and experiences a lower B_effective.

So, the energy required to flip its spin is less than that required for a poorly-shielded nucleus in electron-poor surroundings.

As a result, shielded nuclei have lower absorption frequencies than deshielded nuclei.