Computational investigations of condensed phase systems
Abstract
An all atom model of benzene has been developed and tested. It was used in potential of mean force (PMF, free energy vs benzene center-center distance) calculations to determine the K$\sb{a}$ for benzene dimers in water and chloroform. It was found that the free energy minimum in all solvents corresponds to a T-shaped benzene dimer, not pi-stacked, even in water. The OPLS parameters for butyrolactam and succinimide were used to investigate the experimental preference of lactam dimerization over imide dimerization. By computing the free energy difference between the 3 possible, the experimental trends were reproduced and was further shown to be due to bad secondary coulombic interactions. Furthermore, the higher binding of imides to adenine relative to lactams was also reproduced and explained. Potential functions for the ground state and two transition states of dimethylacetamide (DMA) were developed and used to study solvation effects on the barrier to rotation. It was found that in the gas phase, the two transition states differ by about 4 kcal/mol, but in solution they become nearly isoenergetic. The results in carbon tetrachloride show a much smaller solvent effect than previous experimental data. The Claisen rearrangement is studied using the ab initio minimum energy reaction path and charges fit to the electrostatic potential surface. The solvent stabilization is 3.85 kcal/mol, and is shown to result from enhanced water hydrogen bonding in the transition state. The effects of molecular shape are also discussed.
Degree
Ph.D.
Advisors
Jorgensen, Purdue University.
Subject Area
Organic chemistry|Chemistry
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