电循环环开放反应中的超快速事件
Yusong Liu1, Rui Xu2,3, David M Sanchez4
1Linac Coherent Light Source, SLAC National Accelerator Laboratory, Menlo Park, California, USA;
Annual review of physical chemistry
|February 19, 2025
概括
最近关于电循环反应的研究,重点关注1,3-环二烯衍生物,揭示了超越传统规则的新见解. 超快实验和模拟阐明了圆交叉点的光化学机制和动态.
科学领域:
- 摄影化学的使用.
- 化学动力学 化学动力学
- 物理有机化学 有机化学
背景情况:
- 电循环反应涉及协调的键变化,这是自伍德沃德-霍夫曼规则以来有机化学的基础.
- 传统的理解正在随着新的实验和计算技术而发展.
- 专注于1,3-环二烯及其衍生物提供了具体的案例研究.
研究的目的:
- 审查了解电循环光化学反应的最新进展.
- 探索控制1,3-环二烯和相关化合物的机制.
- 突出先进的实验和计算方法之间的协同作用.
主要方法:
- 时间解析的实验,特别是超快速电子衍射.
- 非adiabatic量子分子动力学模拟,包括ab initio多重产卵.
- 在femtosecond到picosecond时间尺度上分析分子结构动力学.
主要成果:
- 在电循环反应期间阐明分子动力学.
- 详细了解形交叉点的核和电子反应.
- 对研究反应机制的新理论和实验方法的验证.
结论:
- 现代技术为电循环反应动态提供了前所未有的洞察力.
- 伍德沃德-霍夫曼规则的补充是对非反辩效应的更深入的理解.
- 未来的研究可以利用这些方法来探索复杂的光化学转换.
相关概念视频
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
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Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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02:26Base-Catalyzed Ring-Opening of Epoxides
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Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
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01:17Thermal Electrocyclic Reactions: Stereochemistry
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The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
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02:24Acid-Catalyzed Ring-Opening of Epoxides
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Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
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01:26Photochemical Electrocyclic Reactions: Stereochemistry
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The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
Selection Rules: Photochemical Activation
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01:17Pericyclic Reactions: Introduction
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Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic...
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic...
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