氧乙基离子的逐步循环逆转与初始的C-O键裂解
Miguel A Miranda1, M Angeles Izquierdo
1Departamento de Química/Instituto de Tecnología Química UPV- CSIC, Universidad Politécnica de Valencia, Camino Vera s/n, Apdo. 22012, 46022, Valencia, Spain. mmiranda@qim.upv.es
Journal of the American Chemical Society
|June 6, 2002
概括
2,4,6-Triaryl ((thia) pyrlium盐促进了氧乙烯的循环逆转. 2,3-二-4-氧甲基洛克塞坦的基离子经历O-C2裂变,在次微秒内形成四基产物.
科学领域:
- 摄影化学的使用.
- 有机化学 有机化学
- 反应机制 反应机制
背景情况:
- 2,4,6-Triaryl ((thia) pyryllium盐是已知的电子转移光敏感剂.
- 氧化环系统容易受到光化学诱导的循环逆转.
- 对于合成应用来说,了解替代氧乙的碎片化途径至关重要.
研究的目的:
- 通过光敏化研究2,3-二-4-氧甲基洛克塞坦的循环逆转机制.
- 阐明光化学反应中涉及的中间物种和碎片化途径.
- 确定产品形成的动力学和相互竞争的碎片化路径.
主要方法:
- 使用了2,4,6-Triaryl ((thia) pyryllium盐作为光敏感剂.
- 研究了2,3-二-4-氧甲基洛克塞坦的光化学 (1).
- 采用时间分辨率光谱来监测反应中间体和动力学.
主要成果:
- 氧乙 (1) 的基离子经历了阶段性裂变,首先是O-C2 键裂变.
- 一个短暂的中间体定位了氧气上的旋转和碳上的电荷.
- 在微秒以下的时间尺度上,分子内核性攻击导致2,3-二-4-基水 (4a) 的形成.
- 竞争性C3-C4裂变形成了跨静基离子 (λmax = 470 nm).
结论:
- 奥克塞坦的主要光化学途径 (1) 涉及顺序的O-C2裂变和分子内循环.
- 观察到的动力学表明,四二产品的形成速度很快.
- 这项研究提供了对光敏感氧乙循环逆转的详细机理见解.
相关概念视频
03:08Hydroboration-Oxidation of Alkenes
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.
02:04Oxidation of Alkenes: Anti Dihydroxylation with Peroxy Acids
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.
01:46Oxidative Cleavage of Alkenes: Ozonolysis
In ozonolysis, ozone is used to cleave a carbon–carbon double bond to form aldehydes and ketones, or carboxylic acids, depending on the work-up.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
Ozone is a symmetrical bent molecule stabilized by a resonance structure.
03:00Preparation 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...
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...
01:10C–C Bond Formation: Aldol Condensation Overview
Aldol condensation is an important route in synthetic organic chemistry used to generate a new carbon–carbon bond under basic or acidic conditions. The aldol condensation reaction presented in Figure 1 constitutes an aldol addition reaction followed by the dehydration process.
00:57C–C Bond Cleavage: Retro-Aldol Reaction
The reverse of the aldol addition reaction is called the retro-aldol reaction. Here, the carbon–carbon bond in the aldol product is cleaved under acidic or basic conditions to form two molecules of carbonyl compounds. The mechanism of the reaction consists of three steps.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.
In the first step, as depicted in Figure 1, the base deprotonates the β-hydroxy ketone at the hydroxyl group to form an alkoxide ion.