What is shielding and deshielding in NMR? Give an example.

By Ritesh|Updated : November 11th, 2022

In NMR, when the electron density is high around the nucleus, the opposing magnetic field to electrons is also bigger which in turn gives huge shielding. Deshielding is when electron density falls around the nucleus, the magnetic field opposing it reduces and then the nucleus feels more of the external magnetic field.

Shielding

  • The stronger the magnetic field that opposes the electrons and, thus, the more shielding there is, the denser the electron population is all around the nucleus.
  • The chemical shift shifts upfield as a result of the proton's diminished external magnetic field necessitating a lower frequency to achieve resonance (lower ppm).

Example of shielding:

When an atom splits, shielding happens when the electrons that are the furthest from the nucleus are driven away.

Deshielding

  • The opposing magnetic field B0 shrinks as the electron density around a nucleus increases, causing the nucleus to sense more of the external magnetic field.

Example of Deshielding:

Here, it is possible to take into consideration the chemical shift of CH4 protons and CH3Cl protons. The hydrogen nucleus becomes unshielded because the electronegative chlorine atom attracts electron density. The trend will therefore be toward higher ppm. Since CH4's hydrogen nucleus is shielded, the peak is seen on the lower ppm side.

Summary:

What is shielding and deshielding in NMR? Give an example.

When the electron density around the nucleus is high in NMR, the magnetic field that opposes the electrons is likewise increased, providing significant shielding. Deshielding occurs when the nucleus's surrounding electron density decreases, the magnetic field that opposes it weakens, and the nucleus then experiences a stronger external magnetic field.

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