Study of Rotational Isomerism in Fluoroacetyl Fluoride by Microwave Spectroscopy

摘要

Fluoroacetyl fluoride was found to have two distinct sets of pure rotational transitions in the microwave region 8 to 36 kMc/sec, which was identified as arising from two rotamers, one with the two fluorine atoms trans to one another and the other in which they are in the cis positions. These spectra were analysed and moments of inertia obtained. The Stark effect gives the dipole moment components: trans Mu-a = 0.456 plus or minus 0.010 D, Mu-b = 2.63 plus or minus 0.05 D, Mu = 2.67 plus or minus 0.05 D; cis Mu-a = 1.18 plus or minus 0.03 D, Mu-b = 1.68 plus or minus 0.04 D, Mu = 2.05 plus or minus 0.06 D; Mu-c = 0 for both forms. Several sets of satellite lines were observed and assigned to torsionally excited trans molecules, to a skeletal bending mode, and to a combination of these. Relative intensities then gave trans frequencies near 127/cm for the torsion and 265/cm for the bending. Intensities also gave an energy difference, cis-trans, of 910 plus or minus 100 cal/mole. The available data do not completely define the torsional potential function but suggest that the three-fold component may be in the range 1000-1300 cal/mole as in acetyl derivatives. The two-fold component must be dominant to produce the cis instead of gauche minimum. (Author)