Question

Explain why we need/want a large magnetic field in NMR based on the following concepts:

a. kT and the Boltzmann distribution

b.the energy difference between the ground and excited states

c.the net magnetization of the sample

Answer 1

1. At room temperature the population of ground state is very large compared to excited state. Which may interact. Hence large magnetic field is required.

2. There is a energy gap present between ground state and excited state. Hence sometimes the gap may be large such that external energy is required.

3. Each proton is having a local magnetic field due to the presence of other protons which may be shielding that is opposing the external magnetic field or deshielding that is adding to the external magnetic field. In case of shielding effect i.e when attached to electron donating groups the net magnetic field required is large.