[Nescafe]

I read

"the difference in energy between the nuclear spin aligned with and against the applied field depends on how strong the magnetic field is, and also on the properties of the nucleus itself. The stronger the magnetic field we put our nucleus in, the greater the energy difference between the two alignments. Now here is an unfortunate thing about NMR: the energy difference between the nuclear spin being aligned with the magnetic field and against it is really very small—so small that we need a very, very strong magnetic field to see any difference at all"

If the energy difference between the two different aligned spins is two small, then we would have no sensitivity? all peaks would over lab? or would we just not see anything....

I am having a bit of a hard time understanding the importance of this gap, because at the end of the day we want the spins to oppose the field and when they come back to the aligned configuration there is an energy released and that is what is detected.

Nescafe.

[Babcock_Hall]

This is more of a question for a physical chemist, or at least for someone with greater command of the Boltzmann distribution than I have.  However, the smaller the energy difference is, the smaller the population difference between spins that are with the field versus spins against.  The issue is sensitivity; NMR is not a particularly sensitive technique, and it is worse for some nuclei than others.