Trichloromethyl Chloroformate ('Diphosgene'),ClC(O)OCCl_3:Structure and Conformational Properties in the Gaseous and Condensed Phases

摘要

The conformational properties of gaseous trichloromethyl chloroformate (or "diphosgene"),ClC(O)-OCCl_3,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)OCCl_3 exhibits only one conformational form having C_s symmetry with a synperiplanar orientation of the C-O single bond relative to the C=O 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,P2_1,a=5.5578(5) A,b=14.2895(12) A,c=8.6246(7) A,beta=102.443(2) deg,Z=4] likewise consists only of molecules in the syn form.