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

Abstract

The radical anion [CC13 ]− ˙ has been produced by treatment of [(CH3 )3 SiC≡C13 C(═NNHSO2 C6 H4 -p-CH3 )Si(CH3 )3 ] with HO− /F− in the ion source of a mass spectrometer. The stable anion undergoes vertical two-electron oxidation [charge reversal (− CR+ )] in a collision cell to give [CC13 ]+˙ which cyclises to the more stable [cyclo-CC13 ]+˙ over a barrier of only 11 kJ mol−1 [calculated at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311G(d) level of theory], effectively scrambling the three carbon atoms of the cation radical. One-electron Franck–Condon oxidation of [CC13 ]− ˙ yields neutral CC13 C. Theoretical calculations suggest that neutral CCC may undergo a degenerate rearrangement through a cyclic C3 transition state if the excess energy of CCC is ≧104 kJ mol−1 (at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311G(d) level of theory). It is likely that at least a proportion of the CC13 C neutrals formed from [CC13 ]− ˙ should have sufficient energy to effect this reaction, resulting in the scrambling of the13 C label. The neutralisation/reionisation (− NR+ ) spectrum of [CC13 ]− ˙([CC13 ]− ˙→ CC13 C →[CC13 ]+˙ ) shows a pronounced peak corresponding to the parent cation, confirming that neutral CC13 C is stable for the time of the NR experiment (10−6 s). However due to total scrambling of the label in the cation, possible scrambling in the neutral CCC molecule cannot be probed by this experiment. The corresponding− NR− experiment of [CC13 ]− ˙ showed a recovery signal but the sensitivity of the instrument was not sufficient to detect the decomposition fragments of the final radical anion. © 2002 The Royal Society of Chemistry.