What is NMR?
Nuclear Magnetic Resonance (NMR) spectroscopy takes advantage of the natural magnetism present in certain atomic nuclei. The nuclei most often studied in biological applications of NMR are: 1H, 13C, 15N, and 31P. All of these nuclei are stable (non-radioactive) isotopes. When a molecule is placed in a magnetic field, these nuclei act like tiny little bar magnets and align like iron filings. The nuclear bar magnets can align either in the same direction (up) or in the opposite direction (down) as the external magnetic field; these two alignments have different energies. An analogy of this energy difference can be physically experienced by holding the north poles of two magnets together versus holding the north and south poles together. In the first case, they repel and in the latter they attract. It is the difference in energy between these two alignments of the nuclei in the magnetic field that is the fundamental quantity measured by NMR. The great strength of the technique comes from
