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 broken 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 Hg-C bond strengths and are strongly influenced by the electronegativity of the ligands bound to Hg. For instance, the energy barrier decreases by roughly 50% on going from CH3HgCl to CH3HgCH3. The general agreement between computed and experimental trends gives further support to the reaction mechanism.