Ab initio calculations of the barrier to reorientation of the CCl3 group in the trichloroacetic acid, chloral hydrate, and hexachloroethane molecules

Calculations at the RHF/6-31G* level were performed for two most different conformations of trichloroacetic acid, chloral hydrate, and hexachloroethane. These conformations corresponded to the stable and transition rotation angles of the CCl3 group about the C-C bond and were characterized by the highest and lowest energy values. The intramolecular barriers to reorientation of the CCl3 group were determined as the differences of the total energies of these conformations, which gave 7.6, 40.9, and 79.0 kJ/mol, respectively. The influence of the coordination state of the carbon atom bonded with the CCl3 group on the barrier to reorientation is discussed.