Formation of methyl ketenimine (CH₃CH = C = NH) and ethylcyanide (CH₃CH₂C≡N) isomers through successive hydrogenations of acrylonitrile (CH₂ = CH − C≡N) under interstellar conditions: The role of CH₃C^◦H − C≡N radical in the activation of the cyano group chemistry

Possible formation routes of interstellar amino acids have been proposed where the first step consists in the transformation of organic nitriles (RCH₂ − C≡N) into ketenimines (RCH = C = NH). Such a transformation shows high-energy barriers and needs energetic processing to occur. We show in this study that the CN bond could be activated through H-addition reactions to form ketenimines when starting from organic α, β-unsaturated nitriles (C≡N). Consequently, both methyl ketenimine CH₃CH = C = NH and ethylcyanide CH₃CH₂C≡N might have their origin from H₂C = CH − C≡N + 2H reaction occurring on the interstellar icy grains. During the hydrogenation of H₂C = CH − C≡N ice under interstellar conditions, CH₃CH₂C≡N has been formed with an abundance 10 times higher than that of CH₃CH = C = NH. Our measurements lead us to conclude that such a distribution would be directly linked to the π-electrons delocalization H₃C − C^◦H − C≡N ↔ H₃C − CH = C = N^◦ occurring during the reduction of the CC double bond of acrylonitrile.