Carbene chemistry. Part 12. Kinetics of the isomerisation, addition, and insertion reactions of 1,2,2-trifluoroethylidene

Abstract

The carbene CHF₂·CF: has been generated by pyrolysis of trifluoro- and trimethyl-1,1,2,2-tetrafluoroethylsilane [(1a) and (1b)], and relative rates measured for its addition reactions with propene, cis-but-2-ene, and trifluoroethylene, and its insertion reactions with trimethylsilane and isobutane, all relative to the rate of its isomerisation to trifluoroethylene. The isomerisation is a unimolecular reaction in its fall-off region, having p_1/2= 125–430 mmHg at 440–623 K. By fitting RRKM (Forst method) predictions to the fall-off plots, using an estimated A-factor of 10^13.4 s^–1, the activation energy for the isomerisation is found to be ca. 96 kJ mol^–1. The addition and insertion reactions have A-factors which appear to approach the collision rate-constant (10^11.4 dm³ mol^–1 s^–1) and activation energies around 47–50 kJ mol^–1.