Ab initio molecular orbital study on the electrophilic addition of chlorine and bromine to bicyclo[2.2.2]octa-2,5-diene

摘要

The molecular complexes of bicyclo[2.2.2] octa-2,5-diene with chlorine and bromine have been investigated using HF/3-21G~* ab initio method and their stable configurations have been determined. The geometric parameters and stabilization energies related to the complexes have been calculated. The exo and endo complexes are found to be nearly isoenergetic, but an endo selectivity has been observed. The cationic intermediates of the electrophilic addition of chlorine and bromine to bicyclo[2.2.2]octa-2,5-diene have been investigated by HF/3-21G~* and HF/3-21G~(**) ab initio methods. The results obtained reveal that the bridged exo-chloronium cation is relatively more stable than the bridged endo-chloronium cation and the bridged endo-bromonium cation is more stable than the bridged exo-bromonium cation. The rearranged cations have been found to be the most stable ones among the cationic intermediates formed in the reaction. It is plausible that the ionic addition reactions proceed via the most stable cations. Essentially, the rearranged addition products are predicted to form in the ionic addition reactions of chlorine and bromine to bicyclo[2.2.2] octa-2,5-diene.