在UDFT和MCSCF中描述了enediynes的光化学伯格曼循环
A E Clark1, E R Davidson, J M Zaleski
1Department of Chemistry, Indiana University, Bloomington, IN 47405-7102, USA.
Journal of the American Chemical Society
|July 18, 2001
概括
由于竞争性异构化和抽象,通过三联 (13B) 状态的cis-1,5-hexadiyne-3-ene的伯格曼循环化不太可能. 光化学循环在单点 (21A) 潜在能面上更为可信.
科学领域:
- 计算化学计算化学
- 有机光化学 有机光化学
背景情况:
- 伯格曼循环化是有机化学中形成p-中间体的关键反应.
- 了解潜在能量表面 (PES) 对于预测反应路径和可行性至关重要.
研究的目的:
- 为了研究cis-1,5-hexadiyne-3-ene的伯格曼循环的潜在能量表面.
- 为了确定最合理的光化学循环化途径.
主要方法:
- 利用了各种计算化学方法,包括UDFT,CI,CASCI,CASSCF和CASMP2.
- 计算反应的单元和三元潜在能量表面 (PES).
主要成果:
- 三重 (13B) 状态路径不太可能由于竞争的 cis-trans 异构和原子抽象.
- 单点 (21A) 潜在能量表面提供了一个更合理的,虽然不那么外热的光化学循环路线.
- 这种p-中间体具有独特的电子结构,具有单一的碳和二基特征.
结论:
- 在三重路径上,cis-1,5-hexadiyne-3-ene的伯格曼循环化不受到青.
- 光化学循环发生在单片 (21A) PES上更有可能发生.
- 电子结构的p-中间体是复杂的,影响反应动态.
相关概念视频
Structure of Conjugated Dienes
Introduction
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
Conjugated dienes are compounds characterized by the presence of alternating double and single bonds. In a conjugated system like 1,3-butadiene, the unhybridized 2p orbital on each carbon overlaps continuously, allowing the π electrons to be delocalized across the entire molecule. In contrast, this type of overlap does not occur in cumulated and isolated dienes, such as 2,3-pentadiene and 1,4-pentadiene, respectively. Instead, the π electrons remain localized between the double...
Photochemical Electrocyclic Reactions: Stereochemistry
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
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
Diels–Alder Reaction: Characteristics of Dienes
The Diels–Alder reaction brings together a diene and a dienophile to form a six-membered ring. Both components have unique characteristics that influence the rate of the reaction.
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable, the...
Characteristics of the diene
Conformation
The simplest example of a diene is 1,3-butadiene, an acyclic conjugated π system. At room temperature, the molecule exists as a mixture of s-cis and s-trans conformers by virtue of rotation around the carbon–carbon single bond. Although the s-trans isomer is more stable, the...
UV–Vis Spectroscopy: Woodward–Fieser Rules
UV–Visible absorption spectra of conjugated dienes arise from the lowest energy π → π* transitions. The light-absorbing part of the molecule is called the chromophore, and the substituents directly attached to the chromophore are called auxochromes. A strong correlation exists between the absorption maxima, λmax, and the structure of a conjugated π system. The Woodward–Fieser rules predict the value of λmax for a given structure by adding the contributions...
Mass Spectrometry: Cycloalkene Fragmentation
The molecular ions of cycloalkenes undergo fragmentation via a retro-Diels–Alder reaction.


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