The Microwave Spectra, Electric Dipole Moment, and Molecular Structure of 1,1,2,2-Tetrafluorocyclopropane

Article abstract of DOI:10.1021/ja00240a016

The microwave spectra of the normal, monodeuteriated, dideuteriated, and carbon-13 isotopic species of 1,1,2,2-tetrafluorocyclopropane heve been investigated and assigned in the region 26.5-40.0 GHz.The spectral assignments have yielded sufficient data to enable a complete determination of the molecular geometry in the frameworks of both the normal and dideuteriated isotopic species.The partial r_s parameters in the framework of the normal isotopic species are r(C₁C₂) = 1.471(3) Angstroem, r(C₃C_1,2) = 1.497(10) Angstroem, r(C_1,2F) = 1.344(40 Angstroem, r(C₃H) = 1.088(5) Angstroem, θ(FC_1,2F) = 109.9(4) deg and θ(HC₃H) = 118.)(4) deg.The electric dipole moment is determined to be 2.16(3) D.The rotational spectra and symmetry of two low lying vibrational modes were assigned in the dideuteriated isotopic species.The frequencies of the modes were determined from relative intensity measurements to be 188(9) cm^-1 for the symmetric (A) vibrational state and 178(13) cm^-1 for the antisymmetric (B) vibrational state in accord with the previous vibrational assignments.All the ring bonds in 1,1,2,2-tetrafluorocyclopropane are found to shorten relative to cyclopropane with the greater reduction occurring in the C₁-C₂ bond.The FCF and HCH methylene angles, however, are larger in 1,1,2,2-tetrafluorocyclopropane than in 1,1-difluorocyclopropane.These results are related to structural trends established by several experimental and theoretical studies which examined the effect of fluorine substitution on the geometry of substituted cyclopropanes and oxiranes.