What is nuclear spin?
All nuclei carry a charge. In some nuclei this charge “spins”, causing the nucleus to behave like a tiny bar magnet. This is why it aligns with or against the magnetic field of an NMR spectrometer. However unlike a bar magnet, the low energy state is aligned with the field and the high energy state is aligned against the field. Up to now we have been talking about nuclei with a uniform spherical charge distribution. These nuclei are said to have a spin of ½. Protons, 13C and 31P are all spin half nuclei. Note that the most common isotope of carbon, 12C, has no spin and can therefore not be observed using NMR. Nuclei with a non-spherical charge distribution have a spin number I of 1, 3/2 or higher (in steps of ½ ), and are referred to as quadrupolar nuclei. Spin ½ nuclei have two orientations (with or against the field). Spin 1 nuclei have three orientations, spin 3/2 nuclei have 4 orientations, etc. Deuterium is an example of a spin 1 nucleus. Although deuterium is chemically the same
