Ab initio molecular dynamics investigation of the formyl cation in the superacid SbF5/HF

The formyl cation (HCO+) is an intermediate involved in electrophilic formy lation reactions of aromatic compounds. We have employed ab initio molecula r dynamics simulation to investigate free energy profiles along several pos sible reaction paths for CO in the SbF5/HF superacid solution for different concentrations of SbF5. The formation of the HCO+ cation is optimally favo red in the 1:1 SbF5/HF solution. However, no evidence has been found for th e presence of either the isoformyl cation, COH+, or the protoformyl dicatio n, HCOH2+. A novel mechanism for the experimentally observed fast proton ex change in the system CO in 1:1 SbF5/HF is proposed.