Microwave spectroscopy and structures of two conformers of 1H-heptafluoropropane

Two conformations of 1,1,2,2,3,3,3-heptafluoropropane (1H- heptafluoropropane, HFP) have been observed and characterized by its microwave rotational spectrum. The HC₁C₂C₃ dihedral angle is analogous to the CCCC dihedral angle in butane and exhibits both trans and gauche orientations. Rotational transitions of all three selection rules are observed for the gauche conformer, consistent with C₁ symmetry. Only a- and b-type transitions are observed for the trans form, consistent with a 180° dihedral angle and overall C_s symmetry. Computed models at the PBE0/VTZ level are in excellent agreement with experimental results. The structures were characterized by scaling the principal coordinates of the computed models to exactly reproduce the observed second moments.