THEORETICAL CHARACTERIZATION OF THE MECHANISM OF HG-C BOND-CLEAVAGE BY HALOGENIC ACIDS

Ab initio calculations at the MP2 level show that the CH3-Hg bond is b roken by halogenic acids by a one-step mechanism, proceeding through a closed transition state in which, however, bond forming and breaking are not completely synchronous. Activation energies closely parallel H g-C bond strengths and are strongly influenced by the electronegativit y of the ligands bound to Hg. For instance, the energy barrier decreas es by roughly 50% on going from CH3HgCl to CH3HgCH3. The general agree ment between computed and experimental trends gives further support to the reaction mechanism.