Thiol-Michael reactions can be utilized for synthesizing mechanically interlocked molecules and dendritic macromolecules, which have applications in the design of complex polymers and biomedical technologies. These reactions occur rapidly with high yields under mild conditions but are not typically selective when multiple thiols and/or Michael acceptors are present. As polymer reactions must be chemically discriminatory, the ability of thiols to react with many different alkene functionalities is detrimental. By examining the reaction energetics and mechanisms of multiple thiol-ene reactions, we can establish methods to improve thiol-Michael selectivity. Since thiol-vinyl sulfone reactions occur too rapidly to undergo experimental mechanistic analyses, this study will be computational. Specifically, the M06-2X/6-311G(2D,P) and B3LYP/6-31+G(D) levels of theory will be used to examine how different initiators (bases and nucleophiles) may induce different thiol-vinyl sulfone reaction pathways. Initiators are required to generate the initial molecules of thiolate. Thiolate will then react with the Michael acceptor, beginning a rapid catalytic cycle that generates more thiolate to allow the cycle to continue until all reactants are consumed. The catalytic cycle is the key to the speed and high yields of these reactions. There are two generally accepted processes of initial thiolate generation: deprotonation of the thiol by a base or by chain-transfer from the thiol to a charged enolate intermediate. This second process, which is initiated by the nucleophilic attack of the Michael acceptor by the initiator, follows a mechanism by which a nucleophile byproduct is created. Yet no nucleophile byproduct is observed experimentally. To understand this result, we investigate different mechanisms through which byproducts could be consumed. The reaction mechanisms are modeled for each initiator to identify energetic differences, determining which mechanisms are most likely followed. Increased understanding of the initiation mechanisms of thiol-Michael reactions will allow these reactions to be made more selective and functional for polymer synthesis.
"},{"label":"Degree","value":["Bachelor of Arts with Departmental Honors"]},{"label":"Administrative Note","value":"Drupal Node ID: 24067