Nuclear Magnetic Resonance (NMR) spectrometers (aka. Hidden Force Looking Machines) use very large magnets to help study the structure of chemical molecules.
When molecules are inside a magnetic field, they behave in a similar way to tiny bells which can interact with radio waves. ‘Hitting’ the molecules using a short radio signal causes the molecules to ‘ring’ producing a signal which can be detected by the NMR spectrometer. The signal produced by the molecules looks very similar to the shape made by the sound of a bell - the difference is that the NMR signal is detected as an electrical signal by the spectrometer, whilst the bell produces sound waves.
When you hit a bell, the ringing sound produced is made up of several different frequencies (different musical notes) which combine to give the characteristic sound of a bell. Your ear can identify these different frequencies and give you an idea of what sort of size and shape the bell is, just based on the noise that it makes – for example a small hand bell (click to listen) makes a very different noise to Big Ben (click to listen)!
In the same way as our ears can tell the difference between the sounds of the two different bells, the NMR spectrometer can use the signal produced by the molecules to separate out the different frequencies produced by different bits of the molecule. The Chemist (eg. me!) can then use this information to help work out what the molecule looks like.
Depending on how complicated the molecule is, the signal produced may be made up of just one frequency, or several different frequencies all mixed together. A small, simple molecule like Methanol will tend to have only one or two frequencies, whilst a more complicated molecule like Phenacetin will have lots of different frequencies all mixed together.
Since the signals produced by the molecules are very similar to a sound wave it is actually possible to play the NMR signal back allowing us to listen to what our chemicals look like1 (just for fun!). This basically means that we are using the NMR spectrometer as a very big (and very expensive) radio set. One way to do this would just be to connect a speaker directly to the spectrometer and listen to the electrical signals coming off,2 but since I would probably get in trouble if I start messing around with the expensive equipment I have used this bit of software instead, which does the same job.
Methanol (click to listen)
Phenacetin (click to listen)
Because each different molecule interacts with the radio waves at different frequencies (think different sized bells) this means that each molecule can be made to ‘sing’ a different musical note.
Once we have reached this stage, there really is only one logical conclusion:
With thanks to the Pacific Lutheran University FTNMR FID Archive for supplying NMR data used to create this video.
1Yes, this sentence does make sense if you think about it.
2This used to be a very common way of checking instrument settings, requiring ‘not more than half an hour of soldering and wiring’: https://www.chemie.uni-erlangen.de/bauer/music5.html
Andrew is working towards his PhD on "Biogenic Alcohols and Sugars as Sustainable Reductants: A Combined Spectroscopic and Theoretical Approach to the Development of New Homogeneous Catalysts for Dehydrogenation, Hydrogen Transfer and Reverse Water-Gas-Shift Chemistry" with Dr Ulrich Hintermair, Dr Antoine Buchard and Dr John Lowe.