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 hexachloroethan e. These conformations corresponded to the stable and transition rotation a ngles of the CCl3 group about the C-C bond and were characterized by the hi ghest and lowest energy values. The intramolecular barriers to reorientatio n of the CCl3 group were determined as the differences of the total energie s of these conformations, which gave 7.6, 40.9, and 79.0 kJ/mol, respective ly. The influence of the coordination state of the carbon atom bonded with the CCl3 group on the barrier to reorientation is discussed.