STRUCTURAL EFFECTS IN FLUORINATED CYCLOPROPANES - A MICROWAVE STUDY OF CIS-1,1,2,3-TETRAFLUOROCYCLOPROPANE

Microwave and RFMDR spectra of cis-CHFCHFCF2, cis-13CHFCHFCF2, cis-CDFCDFCF2, and cis-13CDFCDFCF2 have been measured between 26.5 and 40.0 GHz using an HP 8400C spectrometer. The a- and c-type transitions were assigned and fit to the quartic Watson Hamiltonian giving A = 3450.445(2) MHz, B = 2402.831(3) MHz, C = 2060.247(3) MHz, ΔJ = 0.39(3) kHz, ΔJK = 0.26(1) kHz, δK = 1.606(9) kHz, δJ = 0.059(1) kHz, and δJK = -0.58(2) kHz for cis-CHFCHFCF2. A structure is derived from the moment of inertia data by fixing three parameters associated with the CF2 group. The rS parameters for the CHFCHF segment of the molecule in the CHFCHFCF2 isotopic frame are r(C2C3) = 1.533(3) A ̊, r(C2,3H) = 1.099(3) A ̊, r(F2 ⋯ F3) = 2.775(2) A ̊, and r(H2 ⋯ H3) = 2.622(2) A ̊. Two algorithms describing the CC and CF bond distances are fitted to gas phase structural data for a series of fluorinated cyclopropane derivatives. A partial test of these algorithms is obtained from the structure of cis-CHFCHFCF2. The structural results are related to theoretical studies of fluorination effects in cyclopropane derivatives. © 1990.