The magnetic moment of H b will be aligned with B 0 in (slightly more than) half of the molecules in the sample, while in the remaining half of the molecules it will be opposed to B 0 . The B eff ‘fel...The magnetic moment of H b will be aligned with B 0 in (slightly more than) half of the molecules in the sample, while in the remaining half of the molecules it will be opposed to B 0 . The B eff ‘felt’ by H a is a slightly weaker if H b is aligned against B 0 , or slightly stronger if H b is aligned with B 0 . In other words, in half of the molecules H a is shielded by H b (thus the NMR signal is shifted slightly upfield) and in the other half H a is deshielded by H b (and the NMR signal shift…
