Detection in the gas phase of unstable ketenimines. Photoelectronic spectrum of N-methylketenimine

The gas-phase generation of the unstable ketenimine (1) and N-methyl-ketenimine (2) has been studied by u.v. photoelectron spectroscopy. Even in short-path pyrolytic conditions, ketenimine isomerizes too quickly to acetonitrile to be detected. On the other hand, the spectrum of N-methyl-ketenimine could be recorded: the first three bands are observed at 8.95, 11.25 and 12.10 eV, respectively, attributed according to MNDO calculations to an A′ ionic state [ejection of an electron from the antisymmetric combination of the π(CC) bond with the nitrogen lone pair], an A″ ionic state [π(CN) bond] and the A′ ionic state arising from the symmetric combination of the π(CC) bond with the nitrogen lone pair. The energetic difference between the first and third bands indicates a weaker interaction between the double CC bond and the nitrogen lone pair than for etheneamine.