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相关概念视频

Preparation of Epoxides03:00

Preparation of Epoxides

9.8K
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...
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Acid-Catalyzed Ring-Opening of Epoxides02:24

Acid-Catalyzed Ring-Opening of Epoxides

9.7K
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...
9.7K
Base-Catalyzed Ring-Opening of Epoxides02:26

Base-Catalyzed Ring-Opening of Epoxides

11.0K
Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
11.0K
Olefin Metathesis Polymerization: Overview01:13

Olefin Metathesis Polymerization: Overview

2.7K
Recently, the development of olefin metathesis polymerization advanced the field of polymer synthesis. Simply put, the reorganization of substituents on their double bonds between two olefins in the presence of a catalyst is known as the olefin metathesis reaction. The use of metathesis reaction for polymer synthesis is called olefin metathesis polymerization.
Ruthenium-based Grubbs catalyst is the most commonly used catalyst for olefin metathesis polymerization. Grubbs catalyst consists of a...
2.7K
Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)01:16

Olefin Metathesis Polymerization: Ring-Opening Metathesis Polymerization (ROMP)

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Ring-opening metathesis polymerization or ROMP involves strained cycloalkenes as starting materials. The mechanism of ROMP proceeds by reacting cycloalkene with Grubbs catalyst to give metallacyclobutane intermediate which undergoes a ring-opening reaction to form new carbene. The new carbene reacts with another molecule of cycloalkene. Repetition of these steps leads to the formation of an unsaturated open-chain polymer product. All these steps are reversible, however, relieving the ring...
3.3K
Sharpless Epoxidation02:57

Sharpless Epoxidation

5.4K
The conversion of allylic alcohols into epoxides using the chiral catalyst was discovered by K. Barry Sharpless and is known as Sharpless epoxidation. The use of a chiral catalyst enables the formation of one enantiomer of the product in excess. This chiral catalyst is mainly a chiral complex of titanium tetraisopropoxide and tartrate ester (specific stereoisomer). The stereoisomer used in the chiral catalyst dictates the formation of the enantiomer of the product. In other words, the use of...
5.4K

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Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy
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Versatile CO2 Transformations into Complex Products: A One-pot Two-step Strategy

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来自环氧化物,乳,无水化物和二氧化碳混合物的化学选择性聚合物

Charles Romain1, Yunqing Zhu1, Paul Dingwall1

  • 1Department of Chemistry, Imperial College London , London SW7 2AZ, U.K.

Journal of the American Chemical Society
|March 23, 2016
PubMed
概括
此摘要是机器生成的。

一种新的催化剂通过在不同聚合物类型之间切换来精确控制聚合物组成. 这一突破允许创建具有工程块序列和可预测的和碳酸结构的聚合物.

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科学领域:

  • 聚合物化学
  • 催化剂
  • 材料科学

背景情况:

  • 控制单体混合物的聚合物组成是聚合物科学中的一个重大挑战.
  • 现有的方法往往无法精确地决定序列和组成.

研究的目的:

  • 调查单个可切换的催化剂,用于环开聚合 (ROP) 和环开共聚合 (ROCOP).
  • 通过单一的催化系统实现对聚合物块序列和可预测组合的控制.

主要方法:

  • 使用实验和理论方法研究催化剂.
  • 研究了四种模型单体的共聚变:e-caprolactone,环氧化物,酸盐和二氧化碳.
  • 分析了单体选择性和催化剂切换行为.

主要成果:

  • 催化剂对不同的单体具有很高的选择性,从而实现了不同的聚合周期.
  • 在聚合物中精确控制块序列的形成.
  • 成功合成了具有可预测的和碳酸盐组成的聚合物.

结论:

  • 单一的催化剂可以有效地控制顺序聚合的直角单体反应性.
  • 了解金属链端组相互作用是工程聚合物块序列的关键.
  • 这种方法为设计具有定制性质的复杂聚合物架构提供了新的途径.