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

The molecular structure and conformational properties of perfluorodimethyl trithiocarbonate, (CF3S)(2)C=S, 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 (DeltaG(0) = 0.2(2) kcal mol(-1)) was derived for the liquid state. Syn/anti describes the orientation of the S-CF3 bonds relative to the C=S bond. The GED investigation resulted in a mixture of 84(12)% (syn,syn) and 16(12)% (syn,anti) conformers for the gas phase (DeltaG(0) = 1.0(5) kcal mol(-1)), The calculations predict energy differences between the two conformers from 0.4. The predominant (syn,syn) form possesses a non-planar sulfur-carbon skeleton of C-2 (B3PW91) to 0.9 (HF) kcal mol symmetry with the S-CF3 bonds rotated out of the CS3 plane (phi (S=C-S-C)= 32(4)degrees). 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. (C) 2000 Elsevier Science B.V. All rights reserved,