Coupled chemistry revisited in the tentative cathodic electropolymerization of 2-butenenitrile

2-Methyl 2-propenenitrile (methacrylonitrile) and 2-butenenitrile (crotononitrile) are vinylic molecules which differ only in the position of a methyl group on the double bond. By combining gas chromatography coupled to chemical ionization mass spectrometry, steric exclusion chromatography and infra-red spectroscopy, along with quantum chemistry based calculations of standard Gibbs energy changes of plausible reactions, we demonstrate that the protons of the methyl group in crotononitrile are acidic in anhydrous acetonitrile, while those of methacrylonitrile are not. In this way, we bring a definite explanation to the fact that methacrylonitrile forms homogeneous films of polymethacrylonitrile (PMAN) on a working electrode subjected to a cathodic polarization in anhydrous acetonitrile, while crotononitrile does not.