THE TORSIONAL POTENTIAL FOR OXALYL CHLORIDE - ARE THERE 2 DISTINCT CONFORMERS

The torsional potential for oxalyl chloride has been investigated in d etail using standard techniques of computational chemistry. Basis sets ranging from 3-21G to TZ2P have been used, with geometry optimizatio ns at both SCF and MP2 levels of theory. Diffuse functions have been s hown to be quantitatively important. MP4DQ energies have been obtained at SCF geometries. The equilibrium structure for oxalyl chloride corr esponds to a planar anti conformation. Details of the torsional potent ial are surprisingly sensitive both to the size of basis and to the le vel of theory used. We have been unable to find convincing theoretical evidence for the existence of a second conformer as a local minimum, though the computed torsional potential is almost flat for Cl-C-C-Cl t orsion angles in the range 80-120-degrees. These findings are discusse d in the light of the available experimental data.