Journal
JOURNAL OF PHYSICAL CHEMISTRY A
Volume 122, Issue 1, Pages 420-430Publisher
AMER CHEMICAL SOC
DOI: 10.1021/acs.jpca.7b10576
Keywords
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Funding
- Arnold and Mabel Beckman Foundation through a Beckman Scholars award
- U.S. Air Force of Scientific Research (AFOSR) [FA95.50-16-1-0051]
- Department of Energy [DE-SC0001093]
- NSF RUI [CHE-1213271]
- U.S. Department of Energy (DOE) [DE-SC0001093] Funding Source: U.S. Department of Energy (DOE)
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [1213271, 1662030] Funding Source: National Science Foundation
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The Bergman cyclization is an important reaction in which an enediyne cyclizes to produce a highly reactive diradical species, p-benzyne. Enediyne motifs are found in natural antitumor antibiotic compounds, such as calicheammicin and dynemicin. Understanding the energetics of cyclization is required to better control the initiation of the cyclization, which induces cell death. We computed the singlet and triplet potential energy surfaces for the Bergman cyclization of (Z)-hex-3-ene-1,5-dryne using the CCSD and EOM-SF-CCSD methods. The triplet enediyne and transition state were found to have C-2 symmetry, which contrasts with the singlet reactant and transition state that possess C-2, symmetry. We analyzed the frontier orbitals of both cyclization pathways to explain the large energetic barrier of the triplet cyclization. Reaction energies were calculated using CCSD(T)/cc-pVTZ single-point calculations on structures optimized with CCSD/cc-pVDZ. The singlet reaction was found to be slightly endothermic (Delta H-rxn = 13.76 kcal/mol) and the triplet reaction was found to be highly exothermic (Delta H-rxn = -33.29 kcal/mol). The adiabatic singlet-triplet gap of p-benzyne, computed with EOM-SF-CCSD/cc-pVTZ, was found to be 3.56 kcal/mol, indicating a singlet ground state.
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