Simulation of Chemical Reactions in Solution With the Combined Quantum Mechanical and Molecular Mechanical Potential

Jaili Gao is funded by a grant from the Theoretical and Computational Chemistry Program to perform computer simulations of chemical reactions in solution. A combined quantum mechanical and molecular mechanical methodology is being developed which combines ab initio Hartree-Fock and molecular orbital techniques with statistical mechanical Monte Carlo simulations to study chemical reactions in solution for very simple chemical species. Analogous calculations on more complex chemical species will employ semiempirical Hamiltonians such as AM1 and INDO/S in conjunction with Monte Carlo simulation techniques. Reactions to be studied include the decarboxylation of 3-carboxybenzisoxazoles and the ionization of t-butyl chloride in aqueous solution.. In addition to studies of chemical reactions in solution, solvent effects on electronic absorption spectra of chromophores will be examined using the same model. Computer simulations of chemical reactions in solution provide important molecular level insights into the factors which influence reaction rates. In particular specific contributions which solvation and accompanying polarization make to lowering barriers to chemical reaction can be studied in detail. Many of the more interesting bond breaking reactions, however, exhibit quantum effects which cannot be modeled effectively using empirical potentials. Gao's approach involves the use of a combined simulation approach which uses Monte Carlo and molecular orbital theory to treat the quantum degrees of freedom undergoing change during the chemical reaction.