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相关概念视频

Preparation of Epoxides03:00

Preparation of Epoxides

Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy acids to...
Acid-Catalyzed Ring-Opening of Epoxides02:24

Acid-Catalyzed Ring-Opening of Epoxides

Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement01:21

[3,3] Sigmatropic Rearrangement of 1,5-Dienes: Cope Rearrangement

The Cope rearrangement is classified as a [3,3] sigmatropic shift in 1,5-dienes, leading to a more stable, isomeric 1,5-diene. The reaction involves a concerted movement of six electrons, four from two π bonds and two from a σ bond, via an energetically favorable chair-like transition state.
Amines to Alkenes: Cope Elimination01:14

Amines to Alkenes: Cope Elimination

Cope elimination reaction involves the conversion of tertiary amines to alkene using hydrogen peroxide under thermal conditions, as depicted in figure 1.
Enolate Mechanism Conventions01:15

Enolate Mechanism Conventions

When a carbonyl compound is treated with a strong base, the α position gets deprotonated to give a resonance-stabilized intermediate called an enolate. Enolates are ambident nucleophiles because they possess two nucleophilic sites that can attack an electrophile owing to the delocalization of the negative charge between the α carbon and oxygen atoms. When the oxygen atom attacks an electrophile, it is called O-attack, whereas electrophilic attack via the α carbon is known as C-attack.
C-attack...
[3,3] Sigmatropic Rearrangement of Allyl Vinyl Ethers: Claisen Rearrangement01:24

[3,3] Sigmatropic Rearrangement of Allyl Vinyl Ethers: Claisen Rearrangement

The Claisen rearrangement is a [3,3] sigmatropic rearrangement of allyl vinyl ethers to unsaturated carbonyl compounds. The rearrangement is a concerted pericyclic reaction proceeding via a chair-like transition state.

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Temperature-programmed Deoxygenation of Acetic Acid on Molybdenum Carbide Catalysts
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循环甲基/循环甲基在表面的重新排列:证据表明在O覆盖的Mo附近发生过渡性阴离子形成

Sean H Wiedemann1, Dae-Hyuk Kang, Robert G Bergman

  • 1Department of Chemistry and Division of Engineering and Applied Sciences, Harvard University, 12 Oxford Street, Cambridge, MA 02138, USA.

Journal of the American Chemical Society
|March 23, 2007
PubMed
概括

这项研究表明,C4-氧化物通过同位素混杂和环膨胀/收缩证明,在O覆盖的Mo(110) 上通过过渡性酸进行重新排列反应. 这些发现支持金属表面的干净,异质解质键裂变.

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科学领域:

  • 表面化学 表面化学
  • 有机金属化学 有机金属化学
  • 催化剂是一种催化剂.

背景情况:

  • 在金属表面上C4-氧化物重新排列反应对于理解催化过程至关重要.
  • 之前对Mo{110) 的研究提出了各种机制,但缺乏对离子中间体的明确证据.

研究的目的:

  • 为了研究C4-氧化物在O覆盖的Mo(110) 上的反应机制.
  • 提供关于Mo(110) 上的环氧化的详细表征.
  • 为了提供异质结合裂变和在重新排列过程中短暂阴离子形成的证据.

主要方法:

  • 温度编程反应光谱学 (TPRS) 是一种温度编程反应光谱技术.
  • 反射吸收红外光谱学 (RAIRS) 是一种反射吸收的技术.
  • 对选择性化环甲醇进行研究,以获得机械学见解.

主要成果:

  • 在Mo{110}上循环氧化物形成和重新排列的详细描述.
  • 强有力的证据表明短暂的阴离子形成,导致环开放的循环甲氧化物重新排列.
  • 对同位素杂乱的观察与长寿命的碳酸介质相一致.
  • 在金属表面表现出干净的,异质的键裂解反应.

结论:

  • 在O覆盖的Mo(110) 上,C4-氧化物的重新排列反应主要通过过渡性阴离子中间体进行.
  • 观察到的环膨胀/收缩反应是阴离子过程的特征.
  • 结果为金属表面反应提供了修订后的反应性模型,对异质碳化合物氧化有影响.