The formation of neutral CCC and its radical cation from the CCC radical anion in the gas phase. A joint experimental and theoretical study

摘要

The radical anion [CC13nC]nu0001u0001n has been produced by treatment of [(CH3)3SiCu0002 u0002 u0002C13nC(u0002 u0002NNHSO2C6H4-p-CH3)Si(CH3)3]nwith HOu0001/Fu0001 in the ion source of a mass spectrometer. The stable anion undergoes vertical two-electron oxidationn[charge reversal (nu0001CRu0003)] in a collision cell to give [CC13nC]nu0003u0001n which cyclises to the more stable [cyclo-CC13nC]nu0003u0001n over anbarrier of only 11 kJ molnu00011n [calculated at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311G(d) level of theory], effectivelynscrambling the three carbon atoms of the cation radical. One-electron Franck–Condon oxidation of [CC13nC]nu0001u0001n yieldsnneutral CC13nC. Theoretical calculations suggest that neutral CCC may undergo a degenerate rearrangement throughna cyclic C3 transition state if the excess energy of CCC is ≥104 kJ molnu00011n (at the CCSD(T)/aug-cc-pVTZ//B3LYP6-311G(d) level of theory). It is likely that at least a proportion of the CC13nC neutrals formed from [CC13nC]nu0001u0001nshould have sufficient energy to effect this reaction, resulting in the scrambling of the n13nC label. The neutralisationreionisation (nu0001NRu0003) spectrum of [CC13nC]nu0001u0001n ([CC13nC]nu0001u0001n CC13nC [CC13nC]nu0003u0001n) shows a pronounced peakncorresponding to the parent cation, confirming that neutral CC13nC is stable for the time of the NR experimentn(10u00016n s). However due to total scrambling of the label in the cation, possible scrambling in the neutral CCC moleculencannot be probed by this experiment. The corresponding nu0001NRu0001 experiment of [CC13nC]nu0001u0001n showed a recovery signalnbut the sensitivity of the instrument was not sufficient to detect the decomposition fragments of the final radicalnanion.