Science Poetry

NMR Spectroscopy

“Of nuclei, resonance magnetic:
Technique useful for research synthetic.
How the sample splits, shields 
In spectrometer’s field 
Can support/reject path theoretic.”

This limerick, posted 10 July 2019, and the one that follows involve topics of spectroscopy: experimental techniques that provide information about a chemical compound based on how the compound interacts with different types of electromagnetic radiation (light).  NMR spectroscopy relies on radio waves, which have longer wavelengths and lower energies than visible light waves.    

“Of nuclei, resonance magnetic: / 
Technique useful for research synthetic.”  
The technique of interest here involves the “resonance magnetic” of nuclei; it is more prosaically known as nuclear magnetic resonance (NMR) spectroscopy.  NMR spectroscopy is particularly useful for organic synthesis research, in which scientists seek to build new molecules, because it provides significant information about molecular structure; it can help answer the question of whether or not a target compound has been achieved. Proton NMR spectroscopy and carbon NMR spectroscopy provide detailed information about the hydrogen and carbon atoms, respectively, within an organic molecule: showing how the “carbon skeleton” fits together.    

“How the sample splits, shields /
In spectrometer’s field /
Can support/reject path theoretic.”

Charged particles (including certain types of nuclei) act as tiny magnets.  Magnets affect one another, and in the presence of an externally applied magnetic field from an instrument called an NMR spectrometer, information about these nuclei can thus be discerned.  

For example, a chemist can infer several pieces of data from the appearance of a proton NMR spectrum. The number of peaks (signals) represents the types of hydrogen atoms present (for example, a spectrum with four different peaks represents a compound with four chemically distinct types of hydrogen).  The intensity of each peak provides information about the number of each type of hydrogen atom.  The splitting patterns (singlets, doublets, etc.) and the chemical shifts (how “shielded” or “deshielded” a particular signal is) seen in each spectrum result from the chemical environments of the different types of hydrogen atoms.  A chemist pieces together this information to discern the identity of a synthesized compound, providing evidence in support or rejection of the “path theoretic”: i.e., the proposed mechanism.