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

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posted on 08.01.2004, 00:00 by Sarah L. Hinchley, Heather E. Robertson, Lorna J. McLachlan, Carole A. Morrison, David W. H. Rankin, Stephen J. Simpson, Emrys W. Thomas
The structure of N-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.