Quantum-Chemical Study of Various Pathways to Carbenium Ions from Olefins and Alkyl Fluorides in the Medium of Hydrofluoric Acid

Elementary reactions of carbenium ion generation from olefins and alkyl fluorides in the medium of hydrofluoric acid are studied by the Hartree–Fock method taking into account electron correlation at the MP2 level and by the DFT (B3LYP) method in the 6-31++G** basis set. Based on enthalpies calculated for these reactions, possible pathways to carbenium ions in the olefin–HF system are determined. A conclusion is drawn that carbenium ions can be formed from olefins by protonation and from the corresponding alkyl fluorides and their protonated forms. It is shown that the heterolytic decomposition of alkyl fluoride in the medium of liquid HF is possible due to the stabilization of carbenium and fluoride ions by hydrogen bonds with HF molecules. The discrete model of microsolvation and the polarizable continuum model (PCM) are used to estimate a decrease in the activation barrier of the heterolytic decomposition of alkyl fluorides due to solvation in the medium of liquid hydrofluoric acid.