The formation of neutral CCCO₂H and HCCCO₂ molecules from anionic precursors in the gas phase: a joint experimental and theoretical study

Abstract

Calculations at the CCSD(T)/aug-cc-pVDZ//B3LYP/6-31G(d) level of theory indicate that the anions -CCCO2H and HCCCO2(-) are stable species in their singlet states. Upon collision-induced, vertical one-electron oxidation under neutralisation-reionisation (-NR+) conditions, they produce the neutral molecules CCCO2H and HCCCO2, respectively. Some of the CCCO2H neutrals should be stable for the duration of the neutralisation-reionisation experiment (10(-6) s), while others will dissociate to CCCO and OH (requires 125 kJ mol(-1)). In contrast, neutral HCCCO2 is expected to be much less stable, and dissociate to HCC and CO2 (37 kJ mol(-1)). Neither CCCO2H nor HCCCO2 is expected to interconvert, or to rearrange to other isomers. The anions -CCCO2H and HCCCO2(-) have been formed in the ion source of the mass spectrometer by the reactions between (CH3)3Si-C[triple bond]C-CO2H and F- and HC[triple bond]C-CO2Si(CH3)3 and F-, respectively. The -NR+ spectrum of -CCCO2H shows a recovery signal and also indicates that the lowest energy dissociation pathway of neutral CCCO2H corresponds to the loss of OH. The -NR+ spectrum of HCCCO2 displays little or no recovery signal, and the spectrum is dominated by the [CO2]+ ion. The experimental observations are in agreement with the predictions of the extensive theoretical studies.