Generation of neutrals from anionic precursors in the gas phase: The anionic, neutral and cationic rearrangements of CCCCHO and CCCHCO to HCCCCO

Abstract

The anions, neutrals and cations of the isomers HCCCCO, CCCHCO and CCCCHO have been studied by experiment and by theory at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory. Anions have been synthesised from precursor neutrals in the source of a mass spectrometer. The anion [HCCCCO] − and (a major proportion of) [CCCHCO] − retain their bond connectivity when energised, but theoretical calculations predict that singlet [CCCCHO] − rearranges to singlet [CCCHCO] − over a barrier of only 28 kJ mol −1. However, triplet [CCCCHO] − is stable under these conditions. Neutralisation/reionisation of [HCCCCO] − results in the sequential two-electron vertical oxidation [HCCCCO] −→HCCCCO→[HCCCCO] +, with the doublet neutral being stable for the microsecond duration of the NR experiment. In contrast, neutralisation of [CCCHCO] − and [CCCCHO] − yield HCCCCO in rearrangements which occur during or subsequent to neutralisation of the anions. Two-electron oxidation (charge reversal, − CR + ) of [CCCHCO] − and [CCCCHO] − both produce the rearranged cation [HCCCCO] + in exothermic reactions.