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Regioselectivity and Stereochemistry of Hydroboration02:36

Regioselectivity and Stereochemistry of Hydroboration

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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...
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Hydroboration-Oxidation of Alkenes03:08

Hydroboration-Oxidation of Alkenes

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In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
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Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation02:47

Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation

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Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
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Catalytic hydrogenation of alkenes is a transition-metal catalyzed reduction of the double bond using molecular hydrogen to give alkanes. The mode of hydrogen addition follows syn stereochemistry.
The metal catalyst used can be either heterogeneous or homogeneous. When hydrogenation of an alkene generates a chiral center, a pair of enantiomeric products is expected to form. However, an enantiomeric excess of one of the products can be facilitated using an enantioselective reaction or an...
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Catalysis

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The presence of a catalyst affects the rate of a chemical reaction. A catalyst is a substance that can increase the reaction rate without being consumed during the process. A basic comprehension of a catalysts’ role during chemical reactions can be understood from the concept of reaction mechanisms and energy diagrams.
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Overview
The acid-catalyzed addition of water to the double bond of alkenes is a large-scale industrial method used to synthesize low-molecular-weight alcohols. An acidic atmosphere is required to allow the hydrogen in the water molecule to act as an electrophile and attack the double bond in an alkene. The addition of a proton to the double bond creates a carbocation intermediate. The proton preferentially bonds to the less substituted end of the double bond to create a more stable carbocation...
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Development of Heterogeneous Enantioselective Catalysts using Chiral Metal-Organic Frameworks MOFs
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构建一个多站点催化剂,以实现高效和高度选择性的化氧化反应.

Liangyao Xue1, Wenjuan Shi1, Dian Song2

  • 1State Key Laboratory of Molecular Engineering of Polymers, Department of Macromolecular Science, Fudan University, Shanghai 200438, China.

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概括

开发高效的化氧化减少 (BOR) 电催化剂是直接化燃料电池 (DBFC) 的关键. 这项研究引入了一种新的多站点催化剂CoFe&AuC,显著提高了BOR性能和燃油效率.

关键词:
玻罗化物氧化反应反应在 CoFe&AuC 的前提下.在DBFC中,DBFC可以在DBFC中进行交易.燃料使用率 燃料利用率多站点催化剂多站点催化剂

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科学领域:

  • 电化学 电化学 电化学
  • 材料科学 材料科学 材料科学
  • 催化剂是一种催化剂.

背景情况:

  • 直接化燃料电池 (DBFCs) 需要高效且具有成本效益的电催化剂来减少化氧化 (BOR).
  • 现有的催化剂往往难以同时实现高BOR率,法拉代效率和低发作潜力.

研究的目的:

  • 开发一种新的多站点催化剂,以增强DBFC中BOR活动和选择性.
  • 研究催化剂组件对BOR性能的协同作用.

主要方法:

  • 合成和表征一个CoFe&AuC多站点催化剂.
  • 在DBFC中使用空气和O2作为氧化剂进行电化学性能测试.
  • 在现场光谱和密度函数理论 (DFT) 计算以阐明催化机制.

主要成果:

  • CoFe&AuC催化剂的峰值功率密度为580mW/cm2 (氧化剂) 和1371mW/cm2 (氧化剂).
  • 性能明显高于对照催化剂 (CoFe&C和AuC).
  • 高电子转移数 (5.4) 和燃油效率 (65.6%) 表示了极好的BOR选择性.

结论:

  • 多站点 CoFe&AuC 催化剂表现出卓越的 BOR 活性和选择性,这是由于 CoFe LDH 和 Au 纳米粒子之间的协奏效应.
  • 这项工作为DBFCs设计高性能多站点电催化剂提出了新策略.