Synthesis, structure and Conformational Properties of Fluoroformyl Chlorodifluoroacetyl Disulfide, FC(O)SSC(O)CF2Cl: Conformational Transferibility in -C(O)SSC(O)- compounds

ERBEN, M. F.; DELLA VÉDOVA, CARLOS OMAR; WILLNER HELGE,; BOESE RONALD,

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

Wiley-VCH Verlag GmbH & Co. KGaA

Lugar: Weinheim, Germany; Año: 2006 vol. 21 p. 4418 - 4425

1434-1948

Pure fluoroformylchlorodifluoroacetyl disulfide, FC(O)SSC(O)CF2Cl, has been prepared by the reaction of FC(O)SCl and CF2ClC(O)SH in quantitative yield. The conformational properties of the novel molecule have been studied by vibrational spectroscopy (IR – gas phase, Raman – liquid phase) and quantum chemical calculations (B3LYP and MP2 methods). The gaseous compound exhibits a conformational equilibrium at room temperature where the most stable form adopts a C1 symmetry and a syn-periplanar (sp) orientation of both carbonyl groups with respect to the disulfide bond. A second form, observed in the IR spectrum of the vapor, corresponds to a conformer in which the carbonyl bond of the FC(O) moiety adopts an anti-periplanar (ap) position with respect to the S–S single bond, and gauche with respect to the ClC–C=O moiety in the chlorodifluoroacetyl group. The experimental free energy difference value ΔG0 = G0 (ap–sp) –G0 (sp–sp) = 1.4(3) kcal/mol (IR) is reproduced well by the B3YLP/6-311+G(3df) (1.1 kcal/mol) and the MP2/6-31G* (1.8 kcal/mol) methods. In addition, the structure of a singlecrystal, grown in situ, was determined by X-ray diffraction analysis at low temperature. The crystalline solid [monoclinic, P21/n, a = 5.579(3) Å, b = 16.615(7), c = 8.455(4) Å, β = 106.876(8)°] consists exclusively of molecules with the (sp– sp) conformation and the usual gauche orientation around the disulfide bond [φ(CS–SC) = 84.2°]. Conformational transferability is thus demonstrated once again for species that contain the –C(O)SSC(O)– group as part of a systematic program designed to analyze the behavior of this class of molecules.