正离子自由基周环反应

一、引言正离子自由基周环反应是指经过正离子自由基环状过渡态的协同反应,包括涉及正离子自由基的 Diels-Alder 反应,烯烃的二聚环加成和烯烃的环丙烷化以及σ-迁移反应等。反应的本质都是单电子接受体催化的周环反应,可由正离子自由基铵盐或正离子自由基聚合物催化、光敏电子     

甲基丙烯酸甲酯增长自由基ESR谱研究

利用高斯分布和构象叠加模型模拟了本体聚合反应全过程增长自由基ESR谱,获得了其构象构成及其随反应的变化,并对产生变化的原因即介质粘度和增长反应对谱的影响进行了讨论。     

用ENDOR和ESR技术研究Friedel-Crafts反应中的自由基离子

本文利用ENDOR和ESR技术检测和鉴定在F—C芳烃烷基化体系中出现的自由基.研究结果表明,所检测到的自由基都属于多核芳烃正离子自由基,即在F-C反应中生成的烷基芳烃化合物通过分子间的Scholl缩合反应生成的多核芳烃被三氯化铝氧化生成的正离子自由基,文中还讨论了多核芳烃的生成及其转变为正离子自由基的机理.     

基于自由基机理的有机硼酯化反应

有机硼酸和硼酸酯化合物是以Suzuki-Miyaura偶联为代表的多种重要化学反应的底物.发展有机硼化合物的高效合成方法具有重要意义.近十年来,基于自由基机理的有机硼酯化反应得以发展,并迅速成为高效构建碳硼键的一类重要方法.自由基硼酯化反应的一般策略为:利用不同反应条件产生的碳自由基活泼中间体与联硼化合物反应,生成相应的有机硼酸或硼酸酯.本文根据反应产生的碳自由基种类的不同,将硼酯化反应分为基于芳基自由基和基于烷基自由基两大部分.各部分依据自由基前体种类的不同,又具体分为基于碳氮、碳氧、碳卤等化学键的硼酯化反应以及羧酸脱羧硼酯化反应.最后,我们进一步总结分析了未来自由基硼酯化反应的研究趋势.     

自由基正离子催化的Diels-Alder环加成反应研究进展

本文回顾了分子间Diels-Alder反应的定义和类型,详细总结了自由基正离子催化的Diels-Alder环加成反应方式,包括铵基阳离子、电化学、三价铁和光催化等方法,对不同催化体系的优缺点进行了说明。同时总结了自由基正离子Diels-Alder环加成反应的现状、面临的挑战,以及未来的发展趋势。     

分子间自由基正离子反应研究进展

自由基正离子含有一个正电荷和一对未成对电子,是很多有机化学反应的重要的活性中间体。文章综述了近几年自由基正离子反应研究进展,主要包括化学氧化剂诱导的自由基正离子反应、可见光诱导的自由基正离子反应、电诱导的自由基正离子反应等方面的研究。     

Fenton反应产生的羟自由基及其清除的电化学方法测定

建立了一种新的测定羟自由基的电化学方法，Fenton反应产生的羟自由基氧化二甲亚砚（DMSO）生成的甲醛与乙酰丙酮、氨发生Hantzsch反应，产物3，5－二乙酰基－1，4－二氢吡啶在－1．20V（vs SCE)处有一灵敏的二阶导数极谱波，通过峰电流变化可间接测定羟自由基；拟定的方法测定了数种清除剂与羟自由基反应的反应速率常量和清除羟自由基的IC50；该法简便可靠，对于抗氧化剂的筛选具有一定的应用价值。     

有机正离子自由基的产生及其结构研究的进展

本文介绍了产生正离子自由基的方法,对正离子自由基的结构特点作了详细的讨论。     

氮自由基环化反应的新进展

三十年前,自由基反应在有机合成中的应用已经非常普遍,但其主要集中在碳自由基的应用上,而杂原子自由基却一直得不到发展.氮自由基环化反应是在近十年内才逐步应用到有机合成中的,它对合成一系列的氮杂环化合物有重要的意义,如内酰胺类、吡咯烷类、生物碱类物质等.从四个方面对氮自由基经环化反应合成多种氮杂环化合物的研究进展做一介绍.     

Formation Mechanism and Emission Spectrum of AlO Radicals in Reaction of Laser－ablated Al Atom and Oxygen

IntroductionLaser ablation has been applied broadly toplasma production,cluster formation,nanometermaterial and thin film material preparation[1,2 ] .Us-ing spectroscopic technique and mass spectrometryto identify the transient species formed in the pro-cess could provide much useful information aboutthe prosperity ofplasma,the mechanism of materi-al growth[3 ,4] .Aluminum is an important metal material andwidely used in industry and daily life. To study thereaction mechanism of Al atoms with…     

Kinetics and Mechanism of the Reaction of Chloroplatinum(II) Complexes with Alkyl Radicals

The reaction between certain platinum(II) complexes and alky radicals produces an unstable organoplatinum(III) intermediate, {Pt^III -R}. The kinetics of this step were evaluated by laser flash photolysis with ABTS² (2,2′-azinobis(3-ethylbenzothiazoline-6-sulfonate) ion) and TMPD (tetramethylphenylenediamine) as kinetic probes. The rate constants for PtCl₄^2? are: k_Pt/10⁸ L mol^?1 s^?1 = 5.2, 2.8 and 0.27 for CH_3, C₂H₅, and CH₂Cl in aqueous solution at pH 1. Those with cis-Pt(NH₃)₂Cl₂ are somewhat smaller, and those for Pt(NH₃)₄²⁺ too small to measure will) this technique. The product analysis indicates that the decomposition of organoplatinum takes place by hydrolysis and (for R = C₂H₅ only) by β-elimination, The kinetic isotope effect on die β-elimination of DCH₂CH₂PtC₄,^2? is k_H/k_D = 1.2. The β-elimination step produces a Pt^III-hydride that releases hydrogen gas and forms {Pt_III-OH}. The short-lived Pt(III) intermediate may disproportionate or oxidize the Co^II complex that is produced in the radical-generating step.     

沸石分子筛在Friedel-Crafts酰基化反应中的应用

本文综述了沸石分子筛在Friedel-Crafts酰基化反应中应用的研究概况,总结了不同类型芳环底物的酰化反应研究成果.Hβ沸石是芳环Friedel-Crafts酰基化反应的优良催化剂,研究惰性和轻度活化芳环的沸石分子筛催化酰化有十分重要的意义.     

ZnS胶体溶液中某些无机盐光化学过程中产生的阴离子自由基的ESR研究

本文用自旋捕捉与ＥＳＲ技术相结合的方法研究了ＺｎＳ胶体溶液中某些无机盐光化学过程中产生的无机阴离子自由基，并对自由基产生的机理进行了讨论     

Cross- and Multi-Coupling Reactions Using Monofluoroalkanes

Carbon-fluorine bonds are stable and have demonstrated sluggishness against various chemical manipulations. However, selective transformations of C−F bonds can be achieved by developing appropriate conditions as useful synthetic methods in organic chemistry. This review focuses on C−C bond formation at monofluorinated sp³-hybridized carbons via C−F bond cleavage, including cross-coupling and multi-component coupling reactions. The C−F bond cleavage mechanisms on the sp³-hybridized carbon centers can be primarily categorized into three types: Lewis acids promoted F atom elimination to generate carbocation intermediates; nucleophilic substitution with metal or carbon nucleophiles supported by the activation of C−F bonds by coordination of Lewis acids; and the cleavage of C−F bonds via a single electron transfer. The characteristic features of alkyl fluorides, in comparison with other (pseudo)halides as promising electrophilic coupling counterparts, are also discussed.     

催化不对称傅-克反应研究进展

催化不对称傅-克反应是构建具有光学活性芳基化合物最有效的方法之一。自从1877年报道了首例傅-克反应后,该反应得到化学家们的关注。最近二十年,许多手性双功能有机小分子催化剂（如金鸡纳碱、手性脯氨醇硅醚、手性磷酸、手性硫脲等）以及金属与手性配体（如手性双氮氧、手性双唑啉、手性席夫碱）形成的配合物催化剂被应用到各类不对称傅-克反应中。本文主要从反应的芳基底物类型分类,对近年来酚、吡咯、呋喃以及噻吩参与的不对称傅-克反应进行简要概述,同时对这类反应所存在的问题和局限性进行总结,并对今后发展方向作了展望。     

n‐Dopants Based on Dimers of Benzimidazoline Radicals: Structures and Mechanism of Redox Reactions

Dimers of 2‐substituted N,N′‐dimethylbenzimidazoline radicals, (2‐Y‐DMBI)₂ (Y=cyclohexyl (Cyc), ferrocenyl (Fc), ruthenocenyl (Rc)), have recently been reported as n‐dopants for organic semiconductors. Here their structural and energetic characteristics are reported, along with the mechanisms by which they react with acceptors, A (PCBM, TIPS‐pentacene), in solution. X‐ray data and DFT calculations both indicate a longer C?C bond for (2‐Cyc‐DMBI)₂ than (2‐Fc‐DMBI)₂, yet DFT and ESR data show that the latter dissociates more readily due to stabilization of the radical by Fc. Depending on the energetics of dimer (D₂) dissociation and of D₂‐to‐A electron transfer, D₂ reacts with A to form D⁺ and A^? by either of two mechanisms, differing in whether the first step is endergonic dissociation or endergonic electron transfer. However, the D⁺/0.5 D₂ redox potentials—the effective reducing strengths of the dimers—vary little within the series (ca. ?1.9 V vs. FeCp₂^+/0) (Cp=cyclopentadienyl) due to cancelation of trends in the D^+/0 potential and D₂ dissociation energy. The implications of these findings for use of these dimers as n‐dopants, and for future dopant design, are discussed.     

The variety of reactions of radical cations derived from 2-diphenylaminothiophene oligomers

ESR spectroelectrochemical measurements of 2-diphenylamino-substituted oligothiophenes 8_m proved the existence of radical cations upon oxidation. Their stability and dimerization depend significantly on the number m of thiophene units. The radical cations and are very reactive and dimerize spontaneously to yield either 2,5-bis(diphenylamino)-2,2′-bithiophene 10₂ or 2,5-bis(diphenylamino)-5,5′-bis(2-thienyl)-3,3′-bithiopene 11₂, respectively. In contrast, the radical cations are highly stable and do not dimerize at all.     

Reaction Mechanism of the Multi‐channel Decomposition Reactions of 1‐Pentenyl Free Radicals

The reactions of 1‐pentenyl decomposition system have been studied extensively at the B3LYP/6‐311++G?? ?? level with Gaussion 98 package. The potential energy surface with zero‐point energy correction was drawn. All reaction channels were fully investigated with the vibrational mode analysis, frontier orbital analysis and electron population analysis to confirm the transition states and reveal the reaction mechanism.     

Complexation of Nitroxide Radicals with Cyclodextrins: Kinetics of Crystal Complex Formation

Using the ESR method in combination with the stop-flow technique the kinetics of crystal complex formation of hydrophobic nitroxide radicals with cyclodextrins has been studied upon mixing cyclodextrin aqueous solutions with nitroxides emulsified in aqueous milieu. The - and -cyclodextrins and the piperidine nitroxide radicals with a OC(O)C_mH_2m+i (m = 7, 10, and 17) substituent in a para-position were used. It was established that the complexation process in the system emulsion of probe–cyclodextrin solution consists of two mainstages. The first stage is the transfer of probes from drops into aqueous solution and the formation of complexes RC_n, where R is the probe, C is cyclodextrin, n = 1, 2 and 3. The second stage is crystal complex formation and growth from solution of RC_n complexes. The results obtained indicate that mainly RC₃ complexes take part in crystallization. It was observed that the characteristic time of crystallization is approximately inversely proportional to the concentration of RC₃ complexes.Equilibrium constants of the processes R + C RC, RC + C RC₂ have been determined. It was found that complexation and further crystallization lead to the formation of monodispersed microcrystals.