Excision of CN− and OCN− from acetamide and some amide derivatives triggered by low energy electrons

Abstract

Low energy electron attachment to acetamide and some of its derivatives shows unique features in that the unimolecular reactions of the transient anions are remarkably complex, involving multiple bond cleavages and the formation of new molecules. Each of the three compounds acetamide (CH₃C(O)NH₂), glycolamide (CH₂OHC(O)NH₂) and cyanoacetamide (CH₂CNC(O)NH₂) shows a pronounced resonance located near 2 eV and decomposing into CN⁻ along a concerted reaction forming a neutral H₂O molecule and the corresponding radical (methyl and methoxy). From glycolamide an additional reaction pathway resulting in the loss of water is operative, in this case generating two fragments and observable via the complementary anion (M–H₂O)⁻. The pseudohalogen OCN⁻ is formed at comparatively lower intensity having a specific energy profile for each of the target molecules. In dibromocyanoacetamide (CBr₂CNC(O)NH₂) the situation changes completely as now comparatively intense CN⁻ and OCN⁻ signals appear already near zero eV. Electronic structure calculations predict that in dibromocyanoacetamide the extra electron resides in a molecular orbital (MO) which is strongly localized at the Br sites. For the other compounds, the relevant MOs are appreciably delocalized showing π*_C=O character.