The NMR phenomenon relies on the interaction of the nuclei of certain atomic isotopes with a static magnetic field. NMR uses a large magnet to probe the intrinsic spin properties of atomic nuclei with the help of electromagnetic radiation. This magnetic field makes the possible spin-states of the nucleus differ in energy, and using NMR techniques the spins can be made to create observable transitions between the spin states. Nuclear Magnetic Resonance is used in quality, control and research for determining the content and purity of a sample as well as its molecular structure *
The principle behind NMR is that many nuclei have spin and all nuclei are electrically charged. If an external magnetic field is applied, an energy transfer is possible between the base energy to a higher energy level (generally a single energy gap). The energy transfer takes place at a wavelength that corresponds to radio frequencies and when the spin returns to its base level, energy is emitted at the same frequency. The signal that matches this transfer is measured in many ways and processed in order to yield an NMR spectrum for the nucleus concerned.

Chemical Shift describes the fact that all nuclei containing an odd number of protons and neutrons have something called a “spin” –a built-in type of movement which is also called resonance. This movement is slightly different for different protons in a given molecule, and can change depending on the chemical environment.

The Zeeman Effect explains what happens when a spectral line—an emission or absorption point in an otherwise uniform spectrum—is split into components while in the presence of a magnetic field.

In NMR spectroscopy, magnetic nuclei are aligned with a constant magnetic field. This alignment is then disturbed by applying an alternating magnetic field to the nuclei. Both NMR spectroscopy and NMR imaging analyze the response of the nuclei to the alternating magnetic field to gather information about the composition of the sample under analysis

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How it works 1. A spinning charge generates a magnetic field, and the resulting spin-magnet has a magnetic moment (μ) proportional to the spin. 2. In the presence of an external magnetic field (B0), two spin states exist, +1/2 and-1/2. The magnetic moment of the lower energy +1/2 state is aligned with the external field, but that of the higher energy -1/2 spin state is opposed to the external field. 3. The difference in energy between the two spin states is dependent on the external magnetic field strength, and is always very small.

Proton Chemical Shift Ranges* | Low Field Region | | High Field
Region |

Applications 1. This is the technology used in magnetic resonance imaging (MRI) 2. Chemists can use NMR to determine the structure of many compounds. Nuclei | Spin | Gyromagetic Ratio (MHz/T) | Natural Abundance (%) | 1H | 1/2 | 42.576 | 99.9985 | 13C | 1/2 | 10.705 | 1.07 | 31P | 1/2 | 17.235 | 100 | 27Al | 5/2 | 11.103 | 100 | 23Na | 3/2 | 11.262 | 100 | 7Li | 3/2 | 16.546 | 92.41 | 29Si | 1/2 | -8.465 | 4.68 | 17O | 5/2 | 5.772 | 0.038 | 15N | 1/2 | -4.361 | 0.368 |

The nucleus consists of elementary particles called neutrons and protons, which contain an intrinsic property called spin. Like electrons, the spin of a nucleus can be described using quantum numbers of I for the spin and m for the spin in a magnetic field. Atomic nuclei with even numbers of protons and neutrons have zero spin and all the other atoms with odd numbers have a non-zero spin.