Chlorodifluorothioacetic Acid, CF₂ClC(O)SH: Synthesis, Characterization, X‐ray Structure and Conformational Properties

Abstract

Chlorodifluoroacetic anhydride, [CF2ClC(O)]2O, and chlorodifluoroacetyl chloride, CF2ClC(O)Cl, react with hydrogen sulfide to yield chlorodifluorothioacetic acid, CF2ClC(O)SH. This novel thiocarboxylic acid has been obtained in pure form and characterized by NMR, IR and Raman spectroscopy. By extrapolation of the vapour pressure curve, log p = 6.102–2068/T (p [bar], T [K]), the boiling point was determined to be 66(1) °C. The melting point of the pure substance is –83(2) °C. The conformational properties of the gas‐phase molecule have been studied by vibrational spectroscopy [IR (vapour), Raman (liquid)] and quantum chemical calculations [B3LYP and MP2 methods with 6‐311++G(d,p) and 6‐311++G(3df,2p) basis sets]. The most stable form has C1 symmetry with a synperiplanar (syn) orientation of the C=O double bond with respect to the S–H single bond whereas in the chlorodifluoroacetyl group the gauche orientation of the ClC–C=O moiety is preferred (gauche‐syn form). The analysis of the IR spectrum of gaseous CF2ClC(O)SH suggests the presence of two other conformations in equilibrium at room temperature. These forms have been fully characterized by high‐level quantum chemical calculations. The structure of a single crystal, grown by a miniature zone‐melting procedure using focused infrared laser radiation, was determined by X‐ray diffraction analysis at low temperature. The crystalline solid [monoclinic, space group C2/c, a = 17.6165(14), b = 5.8848(5), c = 11.0877(9) Å, β = 113.5330(11)°] consists exclusively of molecules adopting the gauche‐syn conformation. These molecules associate, forming pairs of cyclic dimers in the crystal through S–H···O=C hydrogen bonds.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Dimers of Perhaloacetyl Cyanides: CClF2C(O)OC(CN)2CClF2 and CF3C(O)OC(CN) 2CF3. Preparation, Properties, and Spectroscopy

“…(Figure S1, Supporting Information). The chemical shifts are close to those reported for similar compounds. ,, …”

Conformational Behavior of CH3OC(O)SX (X = CN and SCN) Pseudohalide Congeners. A Combined Experimental and Theoretical Study

“…From the conformational point of view, such a small energy difference between both conformers of compound II is of prime interest. – Thus, full geometry optimizations and frequency calculations were performed for each of the most stable structures of CH 3 OC(O)SSCN with the B3LYP and the second-order perturbation theory methods and the 6-31G* and 6-311++G** basis sets. Our results are in perfect agreement with those obtained recently by Ge et al One of the important structural features of this compound is the dihedral angle around the S−S bond, with a computed value of 87.4° at the B3LYP/6-311++G** level of approximation.…”

Conformational preference of chlorothioformate species: molecular structure of ethyl chlorothioformate, ClC(O)SCH2CH3, in the solid phase and NBO analysis

“…For example, the compounds FC(O)SSC(O)CF 3 (Erben et al, 2005) and CH 3 OC(O)SNCO (Vallejos et al, 2007) have been recently investigated using this method. While both compounds exist as an equilibrium mixture of the syn and anti conformers in the liquid and gas phases, only the syn rotamer has been observed in each of the crystals at ca 170 K. A similar picture emerges from the study of CF 2 ClC(O)SH (Erben et al, 2007), which consists exclusively of molecules adopting a syn conformation, favoring the formation of cyclic dimers in the crystal through S-HÁ Á ÁO C hydrogen bonds.…”