Vibrational spectra, gas phase structure and conformational properties of perfluorodimethyl trithiocarbonate, (CF3S)2C[dbnd

Abstract

The molecular structure and conformational properties of perfluorodimethyl trithiocarbonate, (CF3S)2CS, were studied by gas electron diffraction (GED), vibrational spectroscopy and quantum chemical calculations (HF, MP2 and B3PW91 with 6-31G∗ basis sets). From Raman spectra a composition of 60(10)% (syn,syn) and 40(10)% (syn,anti) conformers (ΔG0=0.2(2)kcalmol−1) was derived for the liquid state. Syn/anti describes the orientation of the S–CF3 bonds relative to the CS bond. The GED investigation resulted in a mixture of 84(12)% (syn,syn) and 16(12)% (syn,anti) conformers for the gas phase (ΔG0=1.0(5)kcalmol−1). The calculations predict energy differences between the two conformers from 0.4 (B3PW91) to 0.9 (HF)kcalmol−1. The predominant (syn,syn) form possesses a non-planar sulfur–carbon skeleton of C2 symmetry with the S–CF3 bonds rotated out of the CS3 plane (φ(SC–S–C)=32(4)°). The theoretical calculations predict a planar or nearly planar skeleton for the (syn,anti) conformer. All three computational methods reproduce bond lengths and bond angles very well.