Answer to Question #301191 in Physical Chemistry for Yogesh

Question

The shielded proton requiring a external magnetic field of PMR signal is said to absorb upfield

Answer 1

The higher the electron density around the nucleus, the higher the opposing magnetic field to B0 from the electrons, the greater the shielding. Because the proton experiences lower external magnetic field, it needs a lower frequency to achieve resonance, and therefore, the chemical shift shifts upfield (lower ppms)