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

Abstract The geometric structure of trifluoroacetic anhydride, CF 3 C(O)OC(O)CF 3 , 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 ( C 2v symmetry) with large amplitude torsional motions around the OC bonds and a nonplanar equilibrium structure (C 2 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 C 2 symmetry and φ(COCO)=16.5° and 13.9°, respectively.