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第19讲-芳香族过渡态：环加成和电环反应Lecture 19 - Aromatic Transition States: Cycloaddition and Electrocyclic Reactions |
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| 课程网址: | http://videolectures.net/yalespan125bs2011_mcbride_lec19/ |
| 主讲教师: | J. Michael McBride |
| 开课单位: | 耶鲁大学 |
| 开课时间: | 2014-08-19 |
| 课程语种: | 英语 |
| 中文简介: |  |
| 课程简介: | Cyclic conjugation that arises when p-orbitals touch one another can be as important for transition states as aromaticity is for stable molecules. It is the controlling factor in "pericyclic" reactions. Regiochemistry, stereochemistry, and kinetics show that two new sigma bonds are being formed simultaneously, if not symmetrically, in the 6-electron Diels-Alder cycloaddition. Although thermal dimerization of thymine residues in DNA is forbidden, photochemistry allows the 4-electron cycloaddition. "Electrocyclic" ring opening or closing chooses a conrotatory Möbius pathway, or a disrotatory Hückel pathway, according to the number of electron pairs involved and whether light is used in the process. Dewar benzene provides an example of a very unstable molecule that can be formed photochemically and then persists because of unfavorable orbital overlap in the transition state for ring opening. |
| 关 键 词: | 循环共轭; 芳香性; 过渡态 |
| 课程来源: | 视频讲座网 |
| 数据采集: | 2021-11-12：zkj |
| 最后编审: | 2021-11-12：zkj |
| 阅读次数: | 50 |