Nuclear Magnetic Resonance - A Technique Every Scientist Should Know

Every chemist must know the principles behind NMR. Nuclear magnetic resonance is a technique which utilizes the properties of the nucleus of the atom, in order to understand the structure of the molecule. It is thus an important tool for chemists who would need it for the possible reasons:

1. It can be used to check if a reaction gives the product desired.

2. It can help ensure if the compound is pure

3. It can deduce the structure of the molecule

For these reasons, Nuclear Magnetic Resonance or NMR has become a necessary tool in any organic synthesis department.

One must therefore ask the question, how does it work? The principles of NMR are quite complicated. To simplify this we must take a look at the basics of magnetism. A rotating charged species can create a magnetic field. Thus the nucleus of atoms which has protons and which spins about its axis produces a magnetic field. In NMR spectrometry, the instrument tries to irradiate a radiowave for which the nucleus would resonate, and in return the instrument tries to acquire the signal. However, not every nucleus shows this property.

The hydrogen atom is the most commonly observed atom in NMR. A hydrogen atom has just one proton and therefore it is simple to monitor as well as abundantly found in nature. Also hydrogen atoms which are shielded or deshielded by electrons would give different frequencies of signals and therefore be able to differentiate between functional groups.

One of the main boons of using NMR over other techniques is that the sample being tested is unharmed and it can be recovered. Another advantage is that it is easy to use and one can deduce the chemical structure of an unknown compound to some extent using just one or two experiments within the time span of few minutes.

Advanced techniques in NMR such as 2D NMR, can not only give information about the atoms, but also give information about the bonds connecting the atoms together. Some two dimensional NMR experiments can even predict shapes of the molecules in the solution of the sample.

Three dimensional NMR (3D-NMR) has also been developed and has been useful in deducing structures of proteins and macromolecules. This experiment has several advantages over others for determination of protein structure as you can perform the experiment under physiological conditions similar to those found in the body.

The principles of NMR have also found their way into medicine. Magnetic Resonance Imaging (MRI) uses the same principles of NMR where it too irradiates radiowaves into the body to obtain signals from the hydrogen atoms of water in the different tissues. MRI has been useful in detecting many diseases including tumors.

To summarize, nuclear magnetic resonance techniques have found a wide application in today's scientific world. It is slowly growing in such a manner that not knowing the details of how NMR experiments are performed is almost going to be a crime for any scientist. Most research in chemistry, and some research in fields of biochemistry do require the knowledge of NMR spectrometry.


For more information on NMR spectrometry and nuclear magnetic resonance basics check out The website has very useful information about the technique and has good graphics to explain difficult concepts.

Sam Blazer is a chemist working in a well known institute in USA which requires the use of NMR almost daily. I have used the instrument and would like to share information about this technique.



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