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)3COCCN]-. 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. (C) 2000 Elsevier Science B.V.