Determination of structures of small molecules: NMR spectroscopy

The third and final segment of small molecular structure determination is nuclear magnetic resonance (NMR) spectroscopy, as is one of the strongest tools that chemists have in their arsenal. Like infrared (IR) spectroscopy, it involves illuminating molecules with light of the radiofrequency.

Nuclear magnetic resonance spectroscopy is based on the same technology as MRI, magnetic resonance imaging, that is used for medical and research. MRI will be the focus of another article.

What is spectroscopy?
Molecules can absorb or emit light. How they absorb and emit light can tell us about the molecule itself. The science that involves shining light onto a molecule is called spectroscopy. Studying how molecules emit light is also called spectroscopy.

What is NMR spectroscopy?
Nuclei have their own magnetic field, so when they are placed in an external magnetic field (inside an electromagnet), they will line up with and against the field.

Shining electromagnetic radiation (radiofrequency) onto the molecules can change the numbers aligned with and against the external magnetic field.

What does NMR spectroscopy tell us?
The types and amount of radiofrequency radiation absorbed can tell us several things.

• What atoms are present- carbon, hydrogen, titanium and many others
• How many of each atom is present
• Whether the molecule is symmetric (for example: aniline is symmetric)

• Which atoms are connected to with atoms. Chemists have advanced NMR techniques such as COSY (pronounced like nice and cosy), TOCSY (pronounced toxy) and ROESY (pronounced rosy).
• Which atoms are close in space to other atoms. Chemists have special NMR techniques such as NOESY (pronounced nosy) 

This concludes these series of articles on small molecule structure determination. Hopefully, it was entertaining and gives a glimpse of the world of chemistry. 

I would like to apologize for giving a very abridged stories of mass spectroscopy, NMR spectroscopy and IR spectroscopy. I intentionally wrote this for people with very little chemistry knowledge.