Trichloromethyl chloroformate ("diphosgene"), ClC(O)OCCl 3: Structure and conformational properties in the gaseous and condensed phases

Abstract

The conformational properties of gaseous trichloromethyl chloroformate (or “diphosgene”), ClC(O)- OCCl3, have been studied by vibrational spectroscopy [IR (gas), IR (matrix), and Raman (liquid)] and quantum chemical calculations (MP2 and B3LYP with 6-311G* basis sets); in addition, the structure of a single crystal at low temperature has been determined by X-ray diffraction. ClC(O)OCCl3 exhibits only one conformational form having Cs symmetry with a synperiplanar orientation of the C-O single bond relative to the CdO double bond. The calculated energy difference between the syn and anti forms, 5.73 kcal mol-1 (B3LYP) or 7.06 kcal mol-1 (MP2), is consistent with the experimental findings for the gas and liquid phases. The crystalline solid at 150 K [monoclinic, P21/n, a ) 5.5578(5) Å, b ) 14.2895(12) Å, c ) 8.6246(7) Å, â ) 102.443(2)°, Z ) 4] likewise consists only of molecules in the syn form.