Question

Explain why NMR proton signal from CHCl3 is downfield-shifted verse that of CH3Cl.

Answer 1

NMR spectroscopy

In NMR spectroscopy, greater is the shielding, higher would be the field and lower would be the NMR shift.

In CHCl3, the three Cl pulls electron towards itself, making the proton less shielded, thus the proton appears at much lower field (downfield) position in the NMR spectrum. This means higher NMR shift for this proton.

On the other hand, with one Cl, CH3Cl has greater shielding and thus the protons appear at much higher field. That means a lower chemical shift for CH3Cl protons.