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

The molecular structure and conformational properties of perfluorodimethyl trithiocarbonate, (CF3S)(2)C=S, were studied by gas electron diffraction (G ED), vibrational spectroscopy and quantum chemical calculations (HF, MP2 an d 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 th e gas phase (DeltaG(0) = 1.0(5) kcal mol(-1)), The calculations predict ene rgy differences between the two conformers from 0.4. The predominant (syn,s yn) 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 plan ar or nearly planar skeleton for the (syn,anti) conformer. All three comput ational methods reproduce bond lengths and bond angles very well. (C) 2000 Elsevier Science B.V. All rights reserved,