期刊
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
卷 109, 期 32, 页码 12860-12865出版社
NATL ACAD SCIENCES
DOI: 10.1073/pnas.1209316109
关键词
molecular dynamics; density functional theory; transition state theory; cycloadditions; concerted reaction
资金
- National Science Foundation (NSF) [CHE-1059084, CHE-0910876]
- XSEDE Science Gateways program [TG-CHE090070, TG-CHE040013N]
- John Stauffer Charitable Trust
- Direct For Mathematical & Physical Scien [1059084] Funding Source: National Science Foundation
- Direct For Mathematical & Physical Scien
- Division Of Chemistry [1213976, 0910876] Funding Source: National Science Foundation
- Division Of Chemistry [1059084] Funding Source: National Science Foundation
The time-resolved mechanisms for eight Diels-Alder reactions have been studied by quasiclassical trajectories at 298 K, with energies and derivatives computed by UB3LYP/6-31G(d). Three of these reactions were also simulated at high temperature to compare with experimental results. The reaction trajectories require 50-150 fs on average to transverse the region near the saddle point where bonding changes occur. Even with symmetrical reactants, the trajectories invariably involve unequal bond formation in the transition state. Nevertheless, the time gap between formation of the two new bonds is shorter than a C-C vibrational period. At 298 K, most Diels-Alder reactions are concerted and stereospecific, but at high temperatures (approximately 1,000 K) a small fraction of trajectories lead to diradicals. The simulations illustrate and affirm the bottleneck property of the transition state and the close connection between dynamics and the conventional analysis based on saddle point structure.
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