1,2-FLUORINE SHIFT REARRANGEMENT OF 1,1,1-TRIFLUOROMETHYLCARBENE TO TRIFLUOROETHYLENE

The 1,2-fluorine shift rearrangement of CF3CH to CF2=CHF has been studied by ab initio molecular orbital calculations. The effects of basis functions, electron correlation and zero-point energy (ZPE) are considered. The reaction on the singlet potential energy surface has been computed to be exothermic with a vibrationally corrected MP4SDTQ/6-31++G** reaction energy of 60.1 kcal mol(-1) and a shift barrier of 23.5 kcal mol(-1) which compares well with the experimental estimate of 29 +/- 4 kcal mol(-1). On the triplet surface, the reaction is, however, endothermic, and the corresponding energies are 6.05 and 16.0 kcal mol(-1) at the PMP4SDTQ/6-31++G** + ZPE level of theory. This result for the barrier to the 1,2-fluorine shift in CF3CH differs from the reported prediction that the 1,2-hydrogen shift barriers in triplet CH3CH and CH2=C: are over 50 kcal mol(-1) and about 10 times larger than those for the singlet species.