Electron capture of tetracyanoethylene oxide in the gas phase. Rearrangement of the parent radical anion to form [(NC) 3C] −. A joint experimental and ab initio study

Abstract

Capture of an electron by tetracyanoethylene oxide can initiate a number of decomposition pathways. One of these decompositions yields [(NC) 3C] − as the ionic product. Ab initio calculations (at the B3LYP/6-31+G∗ level of theory) indicate that the formation of [(NC) 3C] − is initiated by capture of an electron into the LUMO of tetracyanoethylene oxide to yield the anion radical [(NC) 2C–O–C(CN) 2] −· that undergoes internal nucleophilic substitution to form intermediate [(NC) 3C–OCCN] −·. This intermediate dissociates to form [(NC) 3C] − ( m/z 90) as the ionic product. The radical (NC) 3C · has an electron affinity of 4.0 eV (385 kJ mol −1). Ab initio calculations show that [(NC) 3C] − is trigonal planar with the negative charge mainly on the nitrogens. A pictorial representation of this structure is the resonance structure formed from three degenerate contributing structures (NC) 2–CCN −. The other product of the reaction is nominally (NCCO) ·, but there is no definitive experimental evidence to indicate whether this radical survives intact, or decomposes to NC · and CO. The overall process [(NC) 2C–O–C(CN) 2] −· → [(NC) 3C] − + (NCCO) · is calculated to be endothermic by 21 kJ mol −1 with an overall barrier of 268 kJ mol −1.