Date of Award

5-2016

Document Type

Thesis

Degree Name

Master of Science (MS)

College/School

College of Science and Mathematics

Department/Program

Chemistry and Biochemistry

Thesis Sponsor/Dissertation Chair/Project Chair

Marc L. Kasner

Committee Member

David S. Talaga

Committee Member

Hendrik Eshuis

Abstract

A computational analysis was performed on the reaction between tetrahydropyran (THP) and atomic bromine in order to gain a better understanding of the energetics of the addition-elimination mechanism as compared to similar chemical reactions. Prior to the reaction energetics study, a separate analysis was performed on substituted tetrahydropyran derivatives in order to optimize the computational methods being used, to understand the extent of the anomeric effect in tetrahydropyran, and to understand solvent contributions to the energies of the tetrahydropyran derivatives. Trial calculations were performed using Hartree-Fock (HF) theory, Density Functional theory (DFT), and second-order Moller-Plesset perturbation (MP2) theory, and it was found that Density Functional theory including Hartree-Fock exchange through the B3LYP hybrid density functional consistently yielded the best results for any given basis set used. It was determined that all calculations would be performed at the B3LYP/aug-cc-pVTZ level of theory. A literature search yielded a similar computational analysis of the reaction between 1,4-dioxane and atomic bromine. Using the B3LYP/aug-cc-pVTZ combination corrected for dispersion, geometry optimizations and transition state calculations verified by intrinsic reaction coordinate (IRC) calculations were performed to construct two "dioxane-like" reaction profiles for the reaction between THP and bromine. It was found that the free energies of activation were very similar for these two pathways, at ΔG1 = 9.01 kcal/mol, and ΔG2 = 9.64 kcal/mol. In 1,4-dioxane, the respective activation energies are ΔGdioxane(1) = 10.88 kcal/mol and ΔGdioxane(2) = 11.26 kcal/mol. Experimental data shows that the temperature-dependent rate constant for the THP + Br reaction is 1-2 orders of magnitude greater than the rate constant of the 1,4-dioxane + Br reaction, so the calculated activation energies are sensible, but need to be verified at a higher level of theory and determined for temperatures other than 298 K. An extended potential energy surface (PES) search resulted in a third viable energetic pathway which has not been studied for 1,4-dioxane. It was determined that this pathway is more energetically favorable than the two dioxane-like pathways with ΔG3 = 8.15 kcal/mol. ΔG rxn = 5.68 kcal/mol for all three pathways, since the reactants and products were held constant.

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