1,4,7-Trimethyloxatriquinane: S(N) 2 在三级碳的反应
Mark Mascal1, Nema Hafezi, Michael D Toney
1Department of Chemistry, University of California Davis, 1 Shields Avenue, Davis, California 95616, USA. mascal@chem.ucdavis.edu
Journal of the American Chemical Society
|August 5, 2010
概括
1,4,7-trimethyloxatriquinane,一种三级基氧盐,抵抗酒解,但通过S(N) 2替代与化物反应. 这种三级碳替代挑战了典型的反应模式,得到了动力学和建模的支持.
科学领域:
- 有机化学 有机化学
- 反应机制 反应机制
- 物理有机化学 有机化学
背景情况:
- 三级酸盐通常是反应性中间体.
- 了解绝缘障碍中心的替代机制至关重要.
- 在核替代反应中oxatriquinanes的行为尚未得到充分证实.
研究的目的:
- 为了描述1,4,7-trimethyloxatriquinane (1) 的合成.
- 为了研究化合物1对核友置换的反应性.
- 阐明第三级碳中心的替代机制.
主要方法:
- 1,4,7-trimethyloxatriquinane的合成. 这是一个很好的方法.
- 与酒精的溶解反应.
- 核性替代反应与亚酸.
- 计算建模. 计算建模.
- 动力学研究.
- 溶剂和盐效应分析.
主要成果:
- 1,4,7-trimethyloxatriquinane (1) 已经成功合成.
- 化合物1证明了与酒精溶解的惰性,即使在高温下也是如此.
- 易于用亚化离子进行替代.
- 证据支持在三级碳中心进行替代的S(N) 2机制,不包括S(N) 1.
- 计算建模和运动数据证实了S(N) 2路径.
结论:
- 在1,4,7-trimethyloxatriquinane中的三级碳中心,S(N) 2机制是可行的替代.
- 这挑战了对核友替代中的固体阻碍的传统理解.
- 这些发现为盐的反应性提供了新的见解.
相关概念视频
SN1 Reaction: Mechanism
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 polar...
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 polar...
Alkenes via Reductive Coupling of Aldehydes or Ketones: McMurry Reaction
The radical dimerization of ketones or aldehydes gives vicinal diols through a pinacol coupling reaction. However, the behavior of titanium metals used for the reaction as a source of electrons is unusual. When the reaction is carried out in the presence of titanium, diols can be isolated at low temperatures. Else titanium further reacts with diols, forming alkenes through the McMurry reaction.
Acid Halides to Alcohols: Grignard Reaction
Organomagnesium halides, commonly known as Grignard reagents, convert acid halides to tertiary alcohols. The reaction requires two equivalents of the Grignard reagent and proceeds via a ketone intermediate.
Grignard reagents are a source of carbanions and function as nucleophiles. The mechanism begins with the nucleophilic attack by the carbanion at the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs,...
Grignard reagents are a source of carbanions and function as nucleophiles. The mechanism begins with the nucleophilic attack by the carbanion at the carbonyl carbon of the acid halide to form a tetrahedral intermediate. Next, the carbonyl group is re-formed, and the halide ion departs,...
Radical Substitution: Hydrogenolysis of Alkyl Halides with Tributyltin Hydride
Radical substitution reactions can be used to remove functional groups from molecules. The hydrogenolysis of alkyl halides is one such reaction, where the weak Sn–H bond in tributyltin hydride reacts with alkyl halides to form alkanes. Here, the reagent Bu3SnH yields tributyltin halide as a byproduct.
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...
The bonds formed in this reaction are stronger than the bonds broken, making it energetically favorable. The reaction follows a radical chain mechanism similar to radical halogenation reactions,...
Preparation of Alcohols via Substitution Reactions
Overview
Alcohols can be synthesized from alkyl halides via nucleophilic substitution reactions. The highly polar carbon-halogen bond in the substrate makes halide a good leaving group. The hydroxide ion or water can act as a nucleophile to take the place of halide and form an alcohol. The substitution reactions occur via two different reaction pathways, SN1 or SN2, depending on the nature of carbon attached to the halide.
Primary alcohols are synthesized from primary alkyl halides, and the...
Alcohols can be synthesized from alkyl halides via nucleophilic substitution reactions. The highly polar carbon-halogen bond in the substrate makes halide a good leaving group. The hydroxide ion or water can act as a nucleophile to take the place of halide and form an alcohol. The substitution reactions occur via two different reaction pathways, SN1 or SN2, depending on the nature of carbon attached to the halide.
Primary alcohols are synthesized from primary alkyl halides, and the...
Preparation and Reactions of Sulfides
Sulfides are the sulfur analog of ethers, just as thiols are the sulfur analog of alcohol. Like ethers, sulfides also consist of two hydrocarbon groups bonded to the central sulfur atom. Depending upon the type of groups present, sulfides can be symmetrical or asymmetrical. Symmetrical sulfides can be prepared via an SN2 reaction between 2 equivalents of an alkyl halide and one equivalent of sodium sulfide.


