Why is electronegativity a factor that influences NMR spectra?

Question

Paisley Boney · Accepted Answer

Electronegativity is an important factor in NMR spectroscopy because it affects the shielding of the nuclei.

When the electrons in a molecule are subjected to an external magnetic field #B_0#, they generate their own magnetic field that opposes #B_0#.

This induced field shields the nearby protons from the full force of #B_0#.

This effect is called diamagnetic shielding.

The nuclei experience only the effective field #B_"eff"#.

(from chemwiki.ucdavis.edu)

The #"Cl"# atom removes enough electron density to shift the frequency of an adjacent proton from δ 0.9 to δ 3.4 ppm.

We see the same effect in #""^13"C"# NMR spectra.

The carbon atom in ethane has a resonance frequency at δ 7 ppm.

In ethanol, the electronegative #"O"# atom deshields the #"C"# atom, and its resonance frequency shifts to δ 58 ppm.

Easton Jones · Answer

undefined Electronegativity influences NMR spectra because it affects the distribution of electron density within a molecule, which in turn influences the local magnetic field experienced by nuclei. This can lead to differences in chemical shift values and peak intensities in the NMR spectrum.