Structure and Conformation of Perfluoromethyloxalate, CF3OC(O)C(O)OCF3, in the Crystal and in the Gas Phase

Abstract

The geometric structure and conformational properties of perfluoromethyloxalate, CF3OC(O)C(O)OCF3, have been studied in the gas phase by gas electron diffraction (GED) and in the solid state by X-ray crystallography. The experimental investigations were supplemented by quantum chemical calculations using the MP2 and B3LYP methods with 6-31G* and 6-31++G(2df) basis sets, respectively. The GED analysis results for the gaseous state in a mixture of two planar conformers with both CO bonds antiperiplanar (ap) to each other (C2h symmetry) or both CO bonds synperiplanar (sp) to each other (C2v symmetry). The ratio ap:sp of 58(12)%:42(12)% corresponds to ΔG0 = 0.19(37) kcal/mol. This value is reproduced satisfactorily by the quantum chemical calculations: 0.42 kcal/mol (MP2) and 0.67 kcal/mol (B3LYP). The presence of a mixture of two conformers with nearly equal contributions is confirmed by the IR(gas) spectrum. In the solid state, four independent molecules with ap conformation (Ci symmetry) occur in the unit cell.