Base catalyzed hydrolysis of methylacetate has been investigated at the ab initio MP2/6-31+G*//HF/6-31+G* level of theory. In the gas phase the B(AC)2-mechanism is favoured over the S(N)2-mechanism by 22 kJ mol-1 in the computed free energy of activation. Two water molecules were added to the tetrahedral intermediate and to the third transition state of the B(AC)2- mechanism to simulate specific solvation of the reacting species. One of the water molecules was found to take part in a water-assisted six-membered cyclic transition state. The polarized continuum solvent model (PCM) was applied to all the optimized geometries to simulate the aqueous bulk medium. The computed free energy of activation of the water-assisted second transition state is 14 kJ mol-1 lower than that of the corresponding non- assisted transition state. The B(AC)2-mechanism in aqueous solution is favoured over the S(N)2-mechanism by 56 kJ mol-1 in free energy of activation. The computed free energies of activation of the B(AC)2-mechanism in aqueous solution are in good agreement with experimental data.
All Science Journal Classification (ASJC) codes
- Condensed Matter Physics
- Physical and Theoretical Chemistry