A quantum chemical study on electrophilic addition

Non-empirical SCF-MO calculations were carried out on two limiting structures of C₂H₄F⁺, corresponding to the cyclic and open valence tautomers, both of which are possible reaction intermediates of the electrophilic addition reaction of F₂ to CH₂ =CH₂. It was found that both species had thermodynamic stability, corresponding to two distinct minima on the energy surface. However, the 2-fluoroethyl carbonium ion showed a greater stability than the fluoronium ion by about 10 kcal/mole.