AB-INITIO STUDY OF BOND STRENGTHS IN CHLORINATED ETHANE MOLECULES ANDETHYL RADICALS

All the bond energies in chlorinated ethane molecules and ethyl free r adicals have been calculated by ab initio molecular orbital methods. T he bond strengths were determined using a direct homolytic bond dissoc iation reaction. All structures of interest were fully optimized at th e MP2/6-31G(d,p) level of theory and were at their global minimum. A s ingle-point energy was calculated for all compounds at the MP4/6-311G( d,p) level of theory. The zero-point energy corrected energy values of the reaction species were used in the calculations. Several trends in bond energies were observed. The results of the calculations showed t hat the alpha-substituted Cl atom has an obvious tendency to increase C-beta-H bond strength and decrease the vicinal C-alpha-H bond strengt h. The Cl atom has a tendency to make other C-Cl bonds weaker, both in radicals and in molecules. The Cl atom strongly affects the thermal s tability of the radicals: all beta-chlorinated ethyl radicals have a v ery weak C-Cl bond which causes them to decompose at low temperatures, whereas alpha-chlorinated radicals are relatively stable at elevated temperature. When a chlorinated ethyl radical decomposes, the most pro bable product is vinyl chloride.