Structures and conformations of trifluoromethyl fluoroformate and perfluorodimethyl carbonate

The conformational properties and geometric structures of trifluoromethyl f luoroformate, CF3OC(O)F (1), and perfluorodimethyl carbonate, (CF3O)(2)CO ( 2), have been studied by matrix IR spectroscopy, gas electron diffraction ( GED), and quantum chemical calculations (MP2 and B3LYP with 6-311 G* basis sets). In both compounds the synperiplanar orientation of the O-CF3 groups relative to the C=O double bond is preferred. If heated Ar/1 and Ar/2 mixtu res are deposited as a matrix at 14 K, new bands appear in the matrix IR sp ectra which are assigned to the anti form of 1 and to the syn/anti form of 2. At room temperature. the contribution of the anti rotamer of 1 is 4% (De ltaH degrees = H degrees (anti) - H degrees (syn) = 1.97(5) kcal/mol), and the contribution of the syn/anti conformer of 2 is estimated to be less tha n 1%. These high-energy conformers are not observed in the GED experiment. The quantum chemical calculations reproduce the structural and conformation al properties of both compounds satisfactorily.