三种反应的激活参数相互转换异构体4-和6-deuteriobicyclo[3.1.0]hex-2-enes
John E Baldwin1, Edmund J Keliher
1Department of Chemistry, Syracuse University, Syracuse, New York 13244, USA.
Journal of the American Chemical Society
|January 17, 2002
概括
在bicyclo[3.1.0]hexenes中,热平衡通过三个不同的途径发生. 这些反应涉及[1,3]-碳转移和"环翻转"过程,所有这些都通过一个共同的二基中间体进行.
科学领域:
- 有机化学 有机化学
- 物理化学 物理化学
- 反应机制 反应机制
背景情况:
- 之前的研究调查了标记的bicyclo[3.1.0]hexenes和thujenes的热平衡.
- 这些调查确定了三种不同的反应途径,导致产品退化.
- 机制包括具有不同立体化学的[1,3]-碳转移和"环翻转"表皮化.
研究的目的:
- 确定已识别的热平衡路径的速率常数的激活参数.
- 为了阐明这些bicyclo[3.1.0]hexene重排的动力控制和中间形成.
主要方法:
- 热平衡反应的动态分析,涉及标记的bicyclo[3.1.0]hexenes.hexenes的热平衡反应.
- 确定单个反应路径的激活能量 (Ea) 和预指数因子 (log A).
- 计算分析以支持机械解释.
主要成果:
- 对三个不同的平衡路径 (kr, kf, ki) 获得了激活参数 (Ea 和 log A).
- 在所有路径中观察到几乎相同的激活参数,表明有一个共同的速率决定步骤.
- 这些数据支持了一种机制,该机制涉及快速分离一种常见的激素中间体.
结论:
- 双循环[3.1.0]的热平衡通过一个共同的二基中间体进行.
- 这种中间体的分离决定了在动力控制下观察到的产品分布.
- 激活参数为统一的机械路径提供了有力的证据.
相关概念视频
02:37Disubstituted Cyclohexanes: cis-trans Isomerism
Depending upon the different spatial orientation of the substituents, the disubstituted cycloalkanes exhibit two types of stereoisomers. The cis isomers have the substituents on the same side of the ring, whereas the trans isomers have the substituents on the opposite sides. These stereoisomers exhibit different physical properties and cannot be interconverted without breaking the carbon-carbon bonds.
In cyclohexane, the substituents can occupy different positions generating distinct isomers.
In cyclohexane, the substituents can occupy different positions generating distinct isomers.
02:33Stereoisomerism of Cyclic Compounds
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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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01:16[4+2] Cycloaddition of Conjugated Dienes: Diels–Alder Reaction
The Diels–Alder reaction is an example of a thermal pericyclic reaction between a conjugated diene and an alkene or alkyne, commonly referred to as a dienophile. The reaction involves a concerted movement of six π electrons, four from the diene and two from the dienophile, forming an unsaturated six-membered ring. As a result, these reactions are classified as [4+2] cycloadditions.
01:28Diels–Alder Reaction Forming Cyclic Products: Stereochemistry
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01:29Diels–Alder Reaction: Characteristics of Dienes
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Conformation
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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...