A novel anion rearrangement. The conversion of [CC(O)(CN)]- to [NCCCO]- in the gas phase: a joint experimental and theoretical study

Abstract

The neutral radical N13CCCO has been made by charge stripping of anion [N13CCCO]- in a collision cell of a ZAB 2HF mass spectrometer. The precursor anion is formed in the ion source of the mass spectrometer by the loss of the elements of MeOH from the anion N13C--CHCO2Me. Neutral N13CCCO can, in turn, be charge stripped to the corresponding cation [N13CCCO]+ which then decomposes by competitive losses of CO and N13C·. No losses of 13CO or NC· are observed in this spectrum: thus, the neutral N13CCCO does not scramble the carbons in the carbon chain during the lifetime (ca. 10-6 s) of the neutral. An attempt to form the neutral radical CC(O)(CN) (which is isomeric with NCCCO) from the precursor anion [CC(O)(CN)]- was unsuccessful, since on formation, [CC(O)(CN)]- undergoes facile rearrangement to the more stable [NCCCO]-. A theoretical investigation at the B3LYP/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory indicates that (i) there are singlet and triplet forms of[CC(O)CN]- which are only 7 kJ mol-1 different in energy, and (ii) both of these ions undergo facile rearrangement to form the respective singlet and triplet forms of [NCCCO]- in strongly exothermic reactions.