The C 2F 2O potential energy surface: a computational study

Abstract

Using ab initio calculations the C 2F 2O potential energy surface was compared with the previously investigated (studies of oxirene or oxacyclopropane and of oxiranylidene or carbenaoxirane) C 2H 2O surface; the CCSD(T)/6-31G(df,p)//MP2(fc)/6-31G(df,p) level was used. Difluorooxiranylidene fragments readily (activation energy 56.1 cf. 122.4 kJ mol −1 for C 2H 2O) to the carbene/CO complex which, unlike CH 2/CO, lies below the ketene in energy (energies relative to difluorooxiranylidene, here and below: complex, −116.3 kJ mol −1, difluoroketene, −106.6 kJ mol −1, transition state connecting complex and difluoroketene, −64.2 kJ mol −1). Oxiranylidene isomerizes to fluorofluorocarbonylcarbene (F–C–CO–F, −8.6 kJ mol −1) by F migration (barrier 211.8 cf. 237.5 kJ mol −1 for H migration in oxiranylidene to give oxirene, which lies 74.6 kJ mol −1 above oxiranylidene; methanoylcarbene, H–C–CO–H, was not a stationary point) which automerizes via difluorooxirene, a transition state (174.8 kJ mol −1). The carbene F–C–COF isomerizes to difluoroketene with a barrier of 57.6 kJ mol −1. Unlike ethynol (93.9 kJ mol −1 below oxiranylidene), fluorofluoroxyethyne (F–CC–OF) is a high-energy molecule (334.8 kJ mol −1), and so too is fluorofluoroxyethenylidene (fluorofluoroxyvinylidene, :CC(OF)F, 501.1 kJ mol −1). A strange nonclassical molecule C 2F 2O (452.8 kJ mol −1) was found which can be described as oxirene with one F bonded to O, one F bonded to C, and the other C trivalent, with a weak single bond to O and a double bond to C. This species (which could be an artifact of the computational level) may be an intermediate in the isomerization of F–C–CO–F to :CC(OF)F (barrier from F–C–CO–F to the species: 473.3 kJ mol −1).