nuclear+magnetic+resonance

If you have ever gotten a medical MRI (magnetic resonance image), then you have experienced a sophisticated version of nuclear magnetic resonance (NMR).



Any odd-numbered nucleus (mass number) has a built-in magnetic moment, meaning it is sensitive to an external magnetic field. The most common nucleus that chemists use in NMR is that of hydrogen (called proton NMR, or 1-H NMR). The second-most common nucleus studied is carbon-13, since about 1 out of every 100 carbon atoms is this isotope.

An NMR device is essentially a giant electromagnet. When a chemical sample is placed in this magnet, all of the odd-numbered nuclei (those that are magnetic) align to this magnet's field when it is turned on. Then, the magnetic field is disturbed by pulsing radio-frequency (RF) electromagnetic radiation. The frequencies that respond to this RF pulse generate information on the structure of the chemical sample.

Hydrogen atoms will generate a signal, which will show up as a peak on the output. If all the hydrogens are identical, and not next to any other hydrogens, they will show up as a single, strong peak. If any other hydrogens are on adjacent carbons, the signal will get split. The amount of splitting tells you how many other types of hydrogens (and thus carbons) there are in the compound. Chemical structure can therefore be interpreted from the output.

Here are some example outputs.











For a much better explanation of proton NMR, please visit James' site, and watch his videos.

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