Title

Computational studies on benzyne diradicals and acceptor-donor cyclopropane reactions with heteroaromatic compounds

Author

Boyi Zhang

Date of Award

2016

Document Type

Thesis

Degree Name

Bachelor of Science

Department

Chemistry

First Advisor

Dr. Carol Parish

Abstract

This study uses methods in computational chemistry to study two different systems. The first are the benzyne isomers. Due to the high reactivity resulting from their open-shell nature, diradical molecules such as the benzyne isomers often serve as intermediates in important reactions such as the formation of buckyballs, polymers, and the combustion of polyaromatic hydrocarbons (PAHs). Buckyballs are currently explored for their potential usage in cancer treatment and molecular wires, and PAHs are known for their damaging effects to the environment. Motivation for understanding how these molecules work stems from a desire to treat cancer more effectively and prevent lasting damage from pollutants like PAHs. Geometry optimizations and single point energies of both the singlet and triplet states of meta- and ortho- benzyne was performed using multi-reference methods(CAS(8,8), MCSCF, MR-CI, MR-AQCC) to characterize the adiabatic and vertical singlet-triplet gaps. Unpaired electron densities were analyzed to determine radical electron coupling. Programs Gaussian09 and Columbus 7.0 were used to obtain data.

The second system involves Acceptor-Donor cyclopropanes. The ring strain present in the three membered carbon ring, along with the movement of electrons between the electron withdrawing and donating groups make a variety of ring-opening, rearrangement, and cycloaddition reactions possible. Experimental studies from the Nolin group have revealed that the possible stepwise reaction between 1,1-cyclopropanediester and heteroaromatic compound benzofuran results in the formation of two products. NMR time studies have shown unidentified transient peaks, suspected to be evidence for a reaction intermediate. Detailed computational calculations were performed on the proposed intermediate in order to determine possible structural conformers populating the reaction sample. Geometry optimizations and NMR calculations were performed at various levels of theory in different solvents. The Gaussian09 computational package was used for this study. Computationally predicted NMR spectra for the lowest energy conformers was compared with experimental data and found to be in good agreement. Thus, computational analysis confirms the presence of the reactive intermediate and identifies the most probable stereomeric conformers.

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