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Radical Reactivity: Steric Effects01:10

Radical Reactivity: Steric Effects

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The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
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Radical Reactivity: Overview01:11

Radical Reactivity: Overview

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Radicals, the highly reactive species, gain stability by undergoing three different reactions. The first reaction involves a radical-radical coupling, in which a radical combines with another radical, forming a spin‐paired molecule. The second reaction is between a radical and a spin‐paired molecule, generating a new radical and a new spin‐paired molecule. The third reaction is radical decomposition in a unimolecular reaction, forming a new radical and a spin‐paired...
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Radical Autoxidation01:20

Radical Autoxidation

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The oxidation of an organic compound in the presence of air or oxygen is called autoxidation. For example, cumene reacts with oxygen to form hydroperoxide. Autoxidation involves initiation, propagation, and termination steps. Many organic compounds are susceptible to autoxidation—especially ethers in the presence of oxygen, which form hydroperoxides. Even though this reaction is slow, old ether bottles contain small amounts of peroxide, which leads to laboratory explosions during ether...
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Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids02:04

Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids

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Diols are compounds with two hydroxyl groups. In addition to syn dihydroxylation, diols can also be synthesized through the process of anti dihydroxylation. The process involves treating an alkene with a peroxycarboxylic acid to form an epoxide. Epoxides are highly strained three-membered rings with oxygen and two carbons occupying the corners of an equilateral triangle. This step is followed by ring-opening of the epoxide in the presence of an aqueous acid to give a trans diol.
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Radical Reactivity: Intramolecular vs Intermolecular01:33

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Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak...
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Temperature Dependence on Reaction Rate02:55

Temperature Dependence on Reaction Rate

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The Collision Theory
Atoms, molecules, or ions must collide before they can react with each other. Atoms must be close together to form chemical bonds. This premise is the basis for a theory that explains many observations regarding chemical kinetics, including factors affecting reaction rates.
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二氧化物:是什么使得这三种激素在动力上具有持久性?

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概括

三重分子氧 (O2) 具有显著的共振稳定性,解释了其在有氧生命中的丰富性和作用. 然而,这种稳定与弱的O-O西格玛键形成对比,使某些氧反应成为可能.

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科学领域:

  • 物理化学
  • 量子化学
  • 生物化学

背景情况:

  • 三重分子氧 (O2) 对于有氧生命至关重要,但表现出独特的反应模式.
  • 了解O2的电子结构和稳定是解释其在生物系统中的丰富性和作用的关键.
  • 之前的研究已经探讨了O2的热力学特性和反应机制.

研究的目的:

  • 测量三元体O2的共振稳定能量.
  • 使用分子轨道 (MO) 和价值键 (VB) 理论阐明这种稳定性的起源.
  • 将共振稳定与观察到的O2原子抽象和寡合反应的热力学不利性相关联.

主要方法:

  • 形成热量和热量的实验性测定.
  • G4 量子化学计算
  • 在分子轨道 (MO) 和价值键 (VB) 理论框架内的分析.

主要成果:

  • 实验和G4计算结果显示,与两个基相比,三重O2的共振稳定能量约为100kcal/mol.
  • 这种巨大的稳定能量源于O2中不配对电子的电子配置,正如MO和VB理论所解释的那样.
  • 原子抽象和寡合化的热力学不利性直接归因于这种显著的共振稳定.

结论:

  • 三重氧的实质性共振稳定解释了它在生态圈中的持久性,支持有氧生命.
  • 尽管 π 系统稳定,但 O-O σ 键的固有弱点使得 O2 容易发生涉及键裂的反应.
  • 反响稳定和 σ 键弱之间的相互作用决定了分子氧的整体反应性.