Heavy-Atom Tunneling in Ring-Opening Pericyclic Reactions - A Computational Exploration
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Though ubiquitous in everyday organic reactions, the phenomenon of tunneling must often be corrected for, and the elusive and subtle nature of its appearance in experimental studies allows it to be a continued interest for computational and organic chemists alike. Tunneling is the result of quantum mechanical principles that allow molecules to essentially “skip” their transition state and go straight to products. Heavy-atom tunneling, specifically of carbon, can have a significant effect on the rate of a reaction for certain temperatures, as evidenced by discrepancies in predicted and observed kinetic isotope effects. This thesis aims to study a reaction that is largely affected by heavy- atom tunneling and to the general features of organic reactions heavily influenced by tunneling using density functional theory computations. Oxetene was chosen as a model system because of the strained nature of its four-atom ring structure, lending itself to a tight transition state and high probability of significant heavy atom tunneling. A similar system where each hydrogen is replaced by a methyl group was also studied to determine the effect of substituent effects on potential KIEs. Significant tunneling, even at room temperatures, was calculated for both of these systems. Further experimental evidence will be gathered to further corroborate the importance of tunneling in such reactions. Because little experimental evidence is known for this effect, though its presence is certain, the search for a concrete way to identify and predict its importance across a diverse array of organic reactions is helpful in modeling these systems.
Huff, Molly Eileen (2016). Heavy-Atom Tunneling in Ring-Opening Pericyclic Reactions - A Computational Exploration. Undergraduate Research Scholars Program. Available electronically from