91. Nuclear Magnetic Resonancerename
yaboiemil's version from 2016-02-04 12:06
Section1. NMR stands for Nuclear Magnetic Resonance.
2. Every atom with an odd number of nucleons (or just odd number of protons) has a
Nuclear Magnetic Moment.
3. Light atomic nuclei with odd numbers of nucleons have 1/2 spin.
4. Magnetic Moment: The force that the magnet can exert on electric currents. A vector
relating the aligning torque of an object from an externally applied magnetic field to the
Relating Magnetic Moment and Angular Momentum:
|Mu symbol||Magnetic Moment|
|Gamma Symbol||Gyromagnetic Ratio|
5. When you apply a magnetic field to all the non-aligned nuclei, they will all align either in the
direction of, or opposite the direction of the magnetic source.
6. Their axis of nuclear rotation will all be the same, and will rotate slightly at a frequency called
the Larmour Procession.
|B||Amplitude of Applied Magnetic Field|
Origin of NMR Signal and Relaxation:7. When subjected to a magnetic field, the aligned atoms will then absorb a quanta of
electromagnetic radiation, and move up to a higher energy level.
8. Then relaxation may occur, whereby the atom releases its electromagnetic signal. This is
and NMR signal.
9. Relaxation times can be Longitudinal (T1) or Transversal (T2).
|Longitudinal||Time taken to return nuclear population to the original state.|
|Transversal||2-10x shorter than Longitudinal.|
10. T1 ranges from 300-2000ms in biological media.
11. The relaxation time can be altered by the presence of PARAMAGNETIC ATOMS and
12. Paramagnetic atoms decrease the time relaxation takes, amplifying the signal.
13. Gadolinium is often used as a contrast agent.
14. Temperature affects it because of the hydrogen bonds in water. These alter the time taken
for the atom to return to its random alignment.
NMR Spectroscopy15. The relaxation time will differ depending on the chemical environment (i.e. the bonds and
surrounding atoms) of the atom.
16. Therefore a C-H bond will produce a different relaxation time to the C=C bond. This enables
you to discover the chemical structure of a compound.