Hexachloroacetone (Cl3C–C([dbnd]O)–CCl3): conformational structure, and the matter of C2 equilibrium symmetry, reinvestigated by gas-phase electron diffraction and ab initio molecular orbital calculations

Abstract

The molecular and conformational structure of hexachloroacetone, Cl3C–CO–CCl3, has been studied using gas-phase electron diffraction (GED) data at a temperature of 300°C, and ab initio molecular orbital calculations. The title compound exists in the gas phase as a single conformer with C2 symmetry, with a twist angle about the C–CCl3 bonds of τ=31.6 (12)° obtained from a quartic potential function tracing the A mode of torsional motion. Some structural parameter values obtained from the dynamic model GED refinements, using results from the theoretical calculations as constraints, are as follows (torsional vibrational average values with estimated 2σ uncertainties): Bond lengths (rg): r(C–C)=1.590 (10) Å, r(CO)=1.202 (11) Å, r(C–Cl)=1.772 (3) Å (average value of the three different C–Cl bonds). Bond angles (∠α): ∠ CCC=123.5 (11)°, ∠CCl=109.5 (3)° (average value of the three different CCCl angles), ∠CCO=118.2 (5)°. Scaled harmonic vibrational force fields were obtained at the HF/6-31G(d) level of theory, and used to calculate shrinkage corrections for all pseudoconformers in the GED dynamic model refinements. The value for the C2v potential barrier (V0=5.17kcalmol−1) in the quartic potential function was obtained from thermal- and zero-point-energy corrected MP2/6-311+G(2d) calculations. The results are discussed and compared with the results for some similar molecules.