The formation of neutral CCC and its radical cation from the CCC radical anion in the gas phase. A joint experimental and theoretical study
Date
2002
Authors
Mc Anoy, A.
Dua, S.
Schroder, D.
Bowie, J.
Schwarz, H.
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Journal of the Chemical Society, Perkin Transactions 2, 2002; 2(10):1647-1652
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Andrew M. McAnoy, Suresh Dua, Detlef Schröder, John H. Bowie and Helmut Schwarz
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Abstract
The radical anion [CC<sup>13</sup> ]<sup>−</sup> ˙ has been produced by treatment of [(CH<inf>3</inf> )<inf>3</inf> SiC≡C<sup>13</sup> C(═NNHSO<inf>2</inf> C<inf>6</inf> H<inf>4</inf> -p-CH<inf>3</inf> )Si(CH<inf>3</inf> )<inf>3</inf> ] with HO<sup>−</sup> /F<sup>−</sup> in the ion source of a mass spectrometer. The stable anion undergoes vertical two-electron oxidation [charge reversal (<sup>−</sup> CR<sup>+</sup> )] in a collision cell to give [CC<sup>13</sup> ]<sup>+˙</sup> which cyclises to the more stable [cyclo-CC<sup>13</sup> ]<sup>+˙</sup> over a barrier of only 11 kJ mol<sup>−1</sup> [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 [CC<sup>13</sup> ]<sup>−</sup> ˙ yields neutral CC<sup>13</sup> C. Theoretical calculations suggest that neutral CCC may undergo a degenerate rearrangement through a cyclic C<inf>3</inf> transition state if the excess energy of CCC is ≧104 kJ mol<sup>−1</sup> (at the CCSD(T)/aug-cc-pVTZ//B3LYP/6-311G(d) level of theory). It is likely that at least a proportion of the CC<sup>13</sup> C neutrals formed from [CC<sup>13</sup> ]<sup>−</sup> ˙ should have sufficient energy to effect this reaction, resulting in the scrambling of the<sup>13</sup> C label. The neutralisation/reionisation (<sup>−</sup> NR<sup>+</sup> ) spectrum of [CC<sup>13</sup> ]<sup>−</sup> ˙([CC<sup>13</sup> ]<sup>−</sup> ˙→ CC<sup>13</sup> C →[CC<sup>13</sup> ]<sup>+˙</sup> ) shows a pronounced peak corresponding to the parent cation, confirming that neutral CC<sup>13</sup> C is stable for the time of the NR experiment (10<sup>−6</sup> 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<sup>−</sup> NR<sup>−</sup> experiment of [CC<sup>13</sup> ]<sup>−</sup> ˙ 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.
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Reproduced by permission of The Royal Society of Chemistry
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Copyright © Royal Society of Chemistry 2002