超结合相互作用如何影响SN2反应中的内在反应性
Leonardo Saravia F1, Jorge Gutiérrez-Flores2, Eduardo H Huerta1
1Instituto de Química, Universidad Nacional Autónoma de México, Circuito Exterior, Ciudad Universitaria, Alcaldía Coyoacán C.P. 04510, Ciudad de México, Mexico. e.hh@quimica.unam.mx.
Physical chemistry chemical physics : PCCP
|October 22, 2025
概括
过度结合在SN2反应中积极调节内在激活障碍,而不仅仅是提供热力学稳定. 本研究使用计算方法量化其对运动参数的直接影响.
科学领域:
- 计算化学的计算化学
- 有机反应机制 有机反应机制
- 量子化学 是一个量子化学.
背景情况:
- 过度结合是一种已知的稳定电子效应.
- 它对动力学参数的直接影响与反应中的热力学稳定性进行了辩论.
- 了解超结合在内在激活障碍中的作用,对于预测反应性至关重要.
研究的目的:
- 调查超联是否直接影响不对称SN2反应中的内在激活屏障.
- 为了区分热力学稳定和通过超联直接动力学调制.
- 量化控制反应性和选择性的电子贡献.
主要方法:
- 使用MP2-SMD (THF) /cc-pVTZ和CCSD (T) -SMD (THF) 方法进行系统的计算研究.
- 通过马库斯理论提取内在激活障碍.
- 使用自然键轨道 (NBO) 分析量化捐助者-接受者相互作用.
- 使用分子中的原子量子理论 (QTAIM) 描述器进行补充分析.
主要成果:
- 在稳定能量和内在激活障碍之间观察到强烈的相关性,与明显障碍不同.
- QTAIM描述符 (电子密度在BCP,VBCP的数量/GBCP的比率) 反映了与内在反应性一致的本地电子环境.
- 与α替代剂系统中的二次稳定相互作用可能会降低内在屏障.
结论:
- 过度结合在SN2反应中积极调节内在反应性,不仅仅是一个被动稳定剂.
- NBO和QTAIM分析是阐明电子对反应性和选择性的贡献的有效工具.
- 隔离内在贡献对于理解基本反应性趋势至关重要.
相关概念视频
02:15SN1 Reaction: Stereochemistry
10.1K
This lesson provides an in-depth discussion of the stereochemical outcomes in an SN1 reaction.
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
In the first step of an SN1 reaction, the bond between the electrophilic carbon and the leaving group ionizes to generate the carbocation intermediate. The second step of the mechanism is the nucleophilic attack.
In the formed carbocation, the positively charged carbon is sp2 hybridized with a trigonal planar geometry. As all the three substituents lie on the same plane, a plane of symmetry for the...
10.1K
02:26SN2 Reaction: Transition State
11.7K
An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
11.7K
02:27Predicting Products: SN1 vs. SN2
15.9K
Nucleophilic substitution reactions of alkyl halides can proceed via an SN1 or an SN2 mechanism. While in SN2 reactions, the nucleophile attacks the substrate simultaneously as the leaving group departs, in SN1 reactions, the substrate first dissociates to give the carbocation intermediate. Various factors such as the structure of the substrate, the strength of the nucleophile, and the nature of the solvent promote one mechanism over the other.
With increased substitution on the alkyl halide,...
With increased substitution on the alkyl halide,...
15.9K
02:27SN2 Reaction: Mechanism
17.1K
The kinetic studies of SN2 reactions suggest an essential feature of its mechanism: it is a single-step process without intermediates. Here, both the nucleophile and the substrate participate in the rate-determining step.
The presence of the more electronegative halogen in the substrate creates a polarized carbon-halide bond. The halide pulls the electron cloud generating an electrophilic center at the carbon atom. Thus, the carbon atom carries a partial positive charge while the halide has a...
The presence of the more electronegative halogen in the substrate creates a polarized carbon-halide bond. The halide pulls the electron cloud generating an electrophilic center at the carbon atom. Thus, the carbon atom carries a partial positive charge while the halide has a...
17.1K
02:23SN2 Reaction: Stereochemistry
11.5K
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not...
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not...
11.5K
02:25SN1 Reaction: Mechanism
14.0K
Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism.
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a...
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a...
14.0K