The role of bridged structures in the mechanism of the reaction between chlorine atom and ethylene

摘要

The potential energy surface for the reaction between a chlorine atom and ethylene was extensively explored by using ab initio methodologies. Two different routes for the 1,2 migration of the chlorine atom were identified. One of them involves a C-2v (B-2(2)) transition structure (TSsb) that directly connects two equivalent structures (P and P') of the 2-chloroethyl radical with the chlorine atom attached either to C1 (P) or to C2 (P') carbon atoms in ethylene (shuttling motion). In the second pathway, the 2-chloroethyl radical (P) coverts into a C-2v ((2)A(1)) intermediate (I-add) through a C-s ((2)A') transition structure (TSadd). Then I-add leads to the 2-chloroethyl radical (P') through a transition structure equivalent to TSadd (TSadd'). The 'indirect shuttling motion' described along this latter route is notably lower in energy and allows one to rationalize some mechanistic aspects experimentally observed in reactions involving haloethyl radicals. (C) 2000 Elsevier Science B.V. All rights reserved. [References: 20]