On the CH3/CF3 substitution effect. The gas-phase structure of 1,1,1,3,3,3-hexafluoropropane

Article abstract of DOI:10.1016/0022-2860(92)85067-Q

The gas-phase structure of CF3CH2CF3 was determined by electron diffraction.The experimental intensities are consistent with a structure possessing C_2v symmetry and the following geometric parameters (r_a distances in Angstroem and <_α angles in degrees, error limits are 3? values): C-H=1.082 (18), C-C=1.518 (4), C-F=1.333 (2), CCC=113.9 (6), FCF=107.7 (1) and HCH=108.7 (not refined).The CF3 groups are tilted by 1.8 (8) deg away from each other.Comparison of these results with the structures of propane, 2-fluoropropane, 2.2-difluoropropane and perfluoropropaneallows a discussion of the effects of fluorination on the C-C- bond lengths and CCC bond angles in this series.The geometries of these compounds have been optimized by ab initio calculations in the HF approximation using different basis sets (3-21G, 6-31G^* and 6-311G^*).The effect of CH3/CF3 substitution on the C-C-bond lengths is reproduced correctly only with basis sets including polarization functions.