Dear Satadru, could you be more specific in which signal is broadening and under which experimental conditions?

Why are you sonicating it? Is the sonication the cause of the broadening? Are you sonicating it inside the magnet during a mearurement or outside the magnet prior to a measurement? The question is not clear.

Luc Alders The peak for acetonitrile which comes at around 2ppm is broadening with increasing time of sonication. My experimental conditions were simple. A sample of acetonitrile is sonicated with a ultrasonication probe for a total of 4 hours, with samples being drawn at 1 hour intervals and then analysed under 1H NMR.

Stan Sykora Sonication is done outside the magnet, and prior to the analysis, the reason for sonication is to gauge what effect does it have on the composition of acetonitrile.

Ultrasonication is having a lot of potentials to break the molecule, if the trace water present in your sample or acetonitrile may getting a break in to free radical or degradation product. Which contribute to peak broadening in 1H NMR.

Satadru Chakrabarty What you describe, if I got it right, might be remarkable. I do not think that what Tabrez Shaikh says is applicable here; a molecule as small as acetonitrile should be 100% stable under sonication (it may be a different story with large proteins).

I recommend that you continue to investigate this effect. Who knows, maybe you are on a track of a discovery! But I have no immediate easy "explanation".

I would appreciate if you could keep me informed, I like mysteries.

Quite interesting indeed! For my understanding, are you sonicating CD3CN and monitoring the residual solvent peak or are you sonicating acetonitrile in another solvent? A

Also, how permanent is the effect? If you measure the sample samples again after awhile, is the signal still broadened? Possibly, you are looking at the effect of radical formation. NMR doesn't like the paramagnetism of unpaired electrons. However, radicals are usually short-lived, so this effect should decay quite rapidly after stopping the sonication. A great way of monitoring radicals is with EPR/ESR. Furthermore, adding a radical scavenger could prevent the peak broadening effect if it is caused by radical formation.

In my opinion there are other points to be considered from an experimental point of view . For example, at what temperature was the sonicating done? Was it done in a closed or open glass? What is the degree of purity of acetonitrile used?

Best regards

Sonicating MeCN should have no effect on line widths. If anything, it might narrow them due to the de-gassing effect. My suspicion is that sonication is leaching something paramagnetic from the container. I wonder what caused you to perform this experiment? Did you have some theory that you were trying to test?

Have you tried another batch of MeCN and sonicated it in a different container? To get to the bottom of this mystery it will be necessary to control the variables. interesting!

Stan Sykora Please have a look here, this is the project I was working on which recently got published

Article An Unexpected Transformation of Organic Solvents into 2D Flu...

Fascinating. Thanks for sharing.