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Date of Award
5-2025
Document Type
Restricted Thesis: Campus only access
Degree Name
Bachelor of Science
Department
Chemistry
First Advisor
Dr. Carol Parish
Abstract
The aim of this thesis is to provide a comprehensive understanding of the energetic effects of chalcogen-phosphorus substituents on enediynes undergoing the Bergman cyclization. To the best of our knowledge, such chalcogen-phosphorus enediynes have not been previously reported. We performed computational quantum calculations at the UCCSD/cc-pVDZ level of theory to analyze the geometries and energetics of two different cyclization pathways, each consisting of the first three chalcogens (oxygen, sulfur, and selenium). The first pathway involved the cyclization of the chalcogen-phosphorus substituents followed by the Bergman cyclization, while the second pathway involved the Bergman cyclization followed by the chalcogen-phosphorus cyclization. Each pathway contains a diradical intermediate and to more accurately understand the energies of these potentially multi-configurational molecules we also performed spin flip characterizations using UHF reference wavefunctions and the EOM-SF-CCSD method. The addition of the chalcogen-phosphorus substituents to the 6-membered acyclic enediyne leads to a lowering in the reaction energy of the Bergman cyclization, from +7.84 kcal/mol for (Z)-hexa-3-ene-1,5-diyne to +6.07, +3.71 and +3.47 kcal/mol for the oxygen, sulfur and selenium congeners, respectively. Additionally, the formation of the doubly-cyclized product is slightly unfavorable for the oxygen species (+0.70 kcal/mol) and energetically favorable for S and Se (–5.50 and –9.05 kcal/mol, respectively). Furthermore, the chalcogen cyclization is energetically favorable whether or not the p-benzynyl diradical moiety is present. We also confirmed the aromaticity of these structures as well as their ground state wavefunctions.
Recommended Citation
Hendler, Marcos, "The Effect of Chalcogen-Phosphorus Substituents on Enediynes Undergoing the Bergman Cyclization" (2025). Honors Theses. 1822.
https://scholarship.richmond.edu/honors-theses/1822
