The shape of perfluorobutyryl fluoride, C3F7COF, in the gas phase

The pure rotational spectrum of perfluorobutyryl fluoride, C3F7COF, was measured using a pulsed nozzle, chirped pulse Fourier transform microwave spectrometer. A total of 280 transitions for the only observed conformer were recorded and analyzed. The rotational constants are A = 1397.4330(1) MHz, B = 619.17456(8) MHz, and C = 592.06831(8) MHz. Quantum chemical calculations and the spectral analysis indicate that the observed conformer is the skew–anti form with calculated dihedral angles ∠ CCCO = 120°, and ∠ CCCC ≈ 170°. Conformational differences between perfluorobutyryl fluoride, perfluorobutyryl chloride, butyryl fluoride and butyryl chloride are discussed.