A quantum mechanical study of the reactivity of methyl chloride on magnesium clusters

Abstract

Quantum mechanical calculations that model the reaction of CH 3Cl on Mg surfaces have been performed at the B3LYP/6-31G** level. The model clusters that were studied contained from 4 to 21 Mg atoms. Although there were large variations in the basic shapes of the clusters investigated, the results seemed to indicate that a site with two separate Mg atoms is involved in the breaking of the C–Cl bond. Previous investigations have speculated on the nature of transition state for an alkyl halide reacting with the magnesium surface. The current work seems to support the idea that the TS involves the simultaneous breaking of the C–Cl bond and the formation of Mg–C and Mg–Cl bonds. The activation energies for the largest clusters are calculated to be on the order of 10 kcal mol −1, which is in reasonable agreement with the recently measured ΔH ‡ of 8 kcal mol −1. The current results do not seem to show any evidence for large amounts of charge transfer from the Mg to the alkyl halide in the precursor complex or even in the transition state. The results do indicate, however, a significant charge transfer in the products that have a chlorine atom bridging two magnesium atoms.