酸的动力学和区域化学
Yexenia Nieves-Quinones1, Daniel A Singleton1
1Department of Chemistry, Texas A&M University , 3255 TAMU, College Station, Texas 77843, United States.
Journal of the American Chemical Society
|November 1, 2016
概括
分子动力学模拟准确地预测了酸的区域化学,而更简单的模型却无法做到这一点. 长时间的模拟表明溶剂重组决定了选择性,挑战了传统的过渡状态理论解释.
科学领域:
- 计算化学
- 物理有机化学
- 反应动态
背景情况:
- 了解电友芳香替代区域化学在有机合成中至关重要.
- 传统模型通常依赖过渡状态能量来预测反应结果.
- 酸的化呈现了一个简化模型可能无法完全捕捉复杂的反应动态的情况.
研究的目的:
- 使用计算方法准确预测化的区域化学.
- 研究过渡状态理论在解释反应选择性的局限性.
- 阐明溶剂和反离子在反应机制中的作用.
主要方法:
- 使用显式溶剂模型进行模拟.
- 分子动力学 (MD) 的轨迹.
- 潜在的平均力 (PMF) 的计算.
主要成果:
- MD轨迹准确地预测了化的区域化学.
- 基于过渡状态理论的简单模型无法解释观察到的选择性.
- PMF计算显示,碰撞复合体没有自由能量障碍,但轨迹需要相当长的时间 (3 ps).
- 由于溶剂和反离子重组,选择性在轨迹的晚期确定.
结论:
- 显式溶剂模拟为酸区域化学提供了准确的预测.
- 反应选择性由晚期溶剂和反离子重组控制,而不仅仅是过渡状态能量.
- 传统的过渡状态理论不足以解释这个系统中的区域选择性.
相关概念视频
01:20Electrophilic Aromatic Substitution: Nitration of Benzene
9.2K
The nitration of benzene is an example of an electrophilic aromatic substitution reaction. It involves the formation of a very powerful electrophile, the nitronium ion, which is linear in shape. The reaction occurs through the interaction of two strong acids, sulfuric and nitric acid.
9.2K
02:36Regioselectivity and Stereochemistry of Hydroboration
9.6K
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
9.6K
01:13meta-Directing Deactivators: –NO2, –CN, –CHO, –CO2R, –COR, –CO2H
7.0K
All meta-directing substituents are deactivating groups. These substituents withdraw electrons from the aromatic ring, making the ring less reactive toward electrophilic substitution. For example, the nitration of nitrobenzene is 100,000 times slower than that of benzene because of the deactivating effect of the nitro group. The first step in an electrophilic aromatic substitution is the addition of an electrophile to form a resonance-stabilized carbocation. The energy diagrams for...
7.0K
01:19Nitrosation of Enols
10.4K
The nitrosation reaction is one of the methods of preparing 1,2-diketones. The enol tautomer of the starting ketone reacts with sodium nitrite in hydrochloric acid, generating the 1,2-diketone after hydrolysis.
10.4K
01:11Reactions at the Benzylic Position: Halogenation
3.8K
Benzylic halogenation takes place under conditions that favor radical reactions such as heat, light, or a free radical initiator like peroxide.
3.8K
01:12Preparation of Nitriles
2.8K
One of the common methods to prepare nitriles is the dehydration of amides. This method requires strong dehydrating agents like phosphorous pentoxide or boiling acetic anhydride for converting amides to nitriles. Another reagent namely, thionyl chloride also accomplishes the dehydration of amides, where amide acts as a nucleophile. The first step of the mechanism involves the nucleophilic attack by the amide on the thionyl chloride to form an intermediate. In the next step, the electron pairs...
2.8K