Theoretical studies of liquid and solution phenomena
Abstract
Potential function parameters in the OPLS format have been generated for several compounds. These include ethers, acids, esters, nitriles and amines. Pure liquid Monte Carlo simulations were performed to test the parameters as well as to probe the structural and thermodynamic properties of the liquids. Analysis of the data for acetic acid revealed that only ca. 7 to 12% of the monomers were involved in cyclic dimers in the liquid. The liquid is composed of chains and open dimers along with some cyclic dimers and very few monomers. An orientational correlation analysis of acetonitrile confirms that this liquid has a significant amount of short range ordering due to the anti-parallel allignment of the permanent dipoles.The ordering is most predominant within a C-C distance of 5.0 A and tails off beyond that. This accounts for ca. 2 solvation shells. Monte Carlo simulations using statistical perturbation theory were used to compute the relative aqueous pK$\sb{\rm a}$'s for methanethiol, methanol, acetonitrile, methylamine and ethane. This was accomplished by perturbing one neutral to another in water as well as interconverting the anions. The computed pK$\sb{\rm a}$ of ethane in water is 52 while the experimental values range from 40 to 60. The structure of the solvent about these anions was also probed. It was found that each anion had between 5 and 7 water molecules strongly associated with it. Relative chloroform/water partition coefficients (log P) were estimated for a number of organic molecules also from Monte Carlo simulations using statistical perturbation theory. Relative log P's were computed from the differences in free energies of solvation obtained from the perturbation of one solute to another in both solvents. This method provided computed log P's in reasonable accord with experimental values and represents an additional way of testing new parameters.
Degree
Ph.D.
Advisors
Jorgensen, Purdue University.
Subject Area
Organic chemistry|Pharmacology
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