Conformational Analysis with Both Experimental and Computational Data for Both Gaseous and Crystalline Phases:  Unexpected Interactions in <i>N</i>-Methyldichloroacetamide

The structure of <i>N</i>-methyldichloroacetamide (MeNHCOCHCl₂) has been elucidated in the gaseous and solid states experimentally by gas electron diffraction and X-ray crystallography, and computationally with ab initio and plane-wave DFT methods. Although the main structural parameters generally agree well, the orientation of the CHCl₂ group relative to the carbonyl oxygen was found to be very different in the solid and gas phases. X-ray crystallography and solid-state plane-wave DFT methods indicate that the bond torsion angle φ(HCCO) is 180.0°, while ab initio and gas electron diffraction methods return φ(HCCO) as −13.1° and −31.8(22)°, respectively. Further investigation of this phenomenon was carried out by using various computational methods. The possibility of intermolecular H···O and Cl···O bonds, which would stabilize the solid-state structure, was investigated by both solid-state plane-wave DFT and single-point ab initio methods. Ab initio SCRF calculations were also employed to evaluate solvent effects on the structure, using the Onsager reaction field model.