Molecular modelling studies on the reactions of fluoroalkenes with sulfur trioxide

The structures, molecular energies and electronic properties of a series of substituted fluoroalkenes and the corresponding alkane sultones, derived f rom the addition of sulfur trioxide to the double bond, have been explored using a combination of molecular modelling and theoretical calculations. Bo th the calculated charge distributions at carbon and the calculated enthalp ies of the addition process show a good correlation with the observed selec tivity of electrophilic attack by the sulfur atom of sulfur trioxide, espec ially for unsymmetrical alkenes where there are two possible sites of addit ion. Mechanistically, the reactions of ethene and tetrafluoroethene with su lfur trioxide proceed via formation of stable pi-complexes to give a transi tion state in the former case which is predicted to have a comparable energ y to that found experimentally for the related reaction of octadec-1-ene.