Gas phase structure and conformational properties of trifluoroacetic anhydride, CF3C(O)OC(O)CF3

The geometric structure of trifluoroacetic anhydride, CF3C(O)OC(O)CF3, has been studied by gas electron diffraction (GED) and quantum chemical calculations (MP2 and B3LYP with 6-31G* basis sets). The GED analysis results in a single conformer with synperiplanar orientation of the two CO bonds. This analysis, however, cannot discriminate between a planar equilibrium structure (C2v symmetry) with large amplitude torsional motions around the OC bonds and a nonplanar equilibrium structure (C2 symmetry) with a low barrier at the planar arrangement. An effective dihedral angle φ(COCO=18(4)° is obtained. Both quantum chemical methods predict a nonplanar equilibrium structure of C2 symmetry and φ(COCO)=16.5° and 13.9°, respectively.