# Why does the 1H NMR spectrum of methacryloyl chloride show two singlets instead of two doublets for vinyl protons?

Based on what I have understood, for methacryloyl chloride there is a geminal coupling of the vinyl protons since they are not chemically equivalent. Why are two singlets observed for vinyl protons instead of two doublets?

• If you look at "peak data" here for methacryloyl chloride ($\ce{C4H5ClO}$), you will see that there is small coupling between the two vinylic hydrogens but also weak allylic coupling to the methyl group. Aug 8 at 18:26

The geminal $$^2\!J_\ce{HH}$$ coupling in terminal alkene $$\ce{CH2}$$ can be pretty small; often on the order of $$\pu{2 Hz}$$. The late Hans Reich's NMR website has a lot of data which you can check out.
(And yes, this is in stark contrast to geminal couplings in diastereotopic, $$\mathrm{sp^3}$$ $$\ce{CH2}$$ groups, which often have large magnitudes!)
If none of that works, it's possible that you might need to rerun the spectrum and increase the acquisition time of the spectrum, but I'd consider that to be quite unlikely for a routine $$\ce{^1H}$$ spectrum.