Interpreting Nuclear Magnetic Resonance Spectroscopy

There are two key things to look at when interpreting an NMR spectrum. The shift of each signal and it’s multiplicity. The further downfield a signal is, the more deshielded the electrons are. That means that the nucleus that creates a signal that is pretty far downfield has something quite electron withdrawing near it. Carboxyl groups withdraw electrons by resonance. This is stronger than inductance so nuclei that are near them show up further downfield than those that stand next to halides or other things that loose electron density by inductance.

Multiplicity tells you how many neighbors a nucleus has. It follows the n + 1 rule. A nucleus will have one more signal than it has neighbors. A proton with two neighbors will be a triplet. A proton with three neighbors will be a quartet.

NMR can only measure asymmetric nuclei like ¹H and ¹³C. In other words, it only measures nuclei with an odd number of particles. Since ¹³C is not as abundant as ¹²C, it takes a longer time to run a carbon NMR experiment.