Ab initio and Monte Carlo calculations for a nucleophilic addition reaction in the gas phase and in aqueous solution

摘要: Energy profiles for the nucleophilic addition of hydroxide ion to formaldehyde in gas phase and aqueous solution have been determined with quantum statistical mechanical methods. Ab initio calculations at 6-31+G* level were utilized study gas-phase potential energy surface. In phase, conversion reactants tetrahedral intermediate is exothermic by 35 kcal/mol proceeds via an ion-dipole complex. Monte Carlo simulations then carried out reacting system solvated 269 water molecules 25/sup 0/C 1 atm solute-solvent functions derived from ab conjunction TIP4P model water. Importance sampling methods employed obtain mean force solution. A substantial activation barrier introduced hydration transition state occurring a C-O separation ca. 2 A. The calculated height free 24-28 10-14 above reactants. Finally, fixed solute corresponding reactants, state, product probe origin barrier.