The dependence of the mechanism of the SiCl bond hydrolysis on the number of the reacting water molecules was investigated in a comprehensive computational study on the prototype molecule H3SiCl. It has been established that the 1:1 reaction proceeds with retention of configuration at Si after a side on oxygen attack, via a 22-24 kcal/mol barrier in a nearly thermoneutral reaction. The barrier of the retention pathway drops to about 16 kcal/mol upon addition of one further water molecule, indicating a significant increase of the reaction rate with a small increase of the water concentration. With a further increase of the number of water molecules, the barrier of the retention process converges to ca. 15 kcal/mol. The barrier of the classical SN2 type reaction with a proton relay with at least three bridging water molecules from the attacking water to the leaving chloride ion drops below this value, depending on the number of the reactant water molecules, furthermore the reaction becomes clearly exothermic as the leaving chloride ion is complexed by the solvation of the available water molecules. A molecular dynamics study with 58 water molecules in the unit cell resulted in a 2 kcal/mol (free energy) barrier via an inversion pathway.
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry