典型无机含氧酸自由基的特性

碳酸自由基、硝酸自由基、磷酸自由基和硫酸自由基是化学反应的重要中间体，都具有氧化性，对污染物在自然和人为环境中的迁移转化会产生重要的影响.文中较为详细地介绍这几种自由基的电极电位、产生方式、检测方法及与有机物的反应方式.总结四种自由基的特性及与有机物的反应方式可发现，四种自由基和羟自由基电极电位不同，导致它们和有机物反应速率的不同；碳酸自由基并不是羟自由基去除剂，对于一些容易被氧化的化合物，碳酸自由基氧化效果比羟自由基好；四种自由基均可由羟自由基转化而来，并且这四种自由基和羟自由基与有机物反应方式基本一致，都通过电子转移、夺氢和加成的方式进行.可以预测四种自由基和羟自由基降解有机物的机理将非常相似，今后应研究四种自由基与羟自由基相互转化的规律，以及与代表性有机物的反应机理.     

Free-Radical Reaction of 2-Vinylcyclopropane-1,1-dicarboxylate with Alkynes

A free-radical reaction of dimethyl 2-vinylcyclopropane-1,1-dicarboxylate with electron rich alkynes giving cyclopentene systems is described. This reaction can be achieved with p-toluenesulfonyl chloride and phenyldisulfide as radical precursors.     

Quantum chemical investigation of the reaction of O(3 P 2) with certain hydrocarbon radicals

The reaction of ground-state atomic oxygen [O(³ P ₂)] with methyl, ethyl, n-propyl and isopropyl radicals has been studied using the density functional method and the complete basis set model. The energies of the reactants, products, reaction intermediates and various transition states as well as the reaction enthalpies have been computed. The possible product channels and the reaction pathways are identified in each case. In the case of methyl radical the minimum energy reaction pathway leads to the products CO + H₂ + H. In the case of ethyl radical the most facile pathway leads to the products, methanal + CH₃ radical. For propyl radical (n- and iso-), the minimum energy reaction pathways would lead to the channel containing ethanal + methyl radical.     

The Studies of Free Radical Cyclization Reactions Mediated by Sulfonyl Chloride (II)

A study on the free radical cyclization reaction of substituted 1,6-dienes mediated by p-toluenesulfonyl chloride is described.     

The Studies of Free Radical Cyclization Reactions Mediated by Sulfonyl Chloride (I)

A study of the free racinoal reaction of vinylcycloprelpane mediated by p-toluenesulfonyl chloride is described.     

Exploring the Biosynthetic Potential of TsrM,a B12-dependent Radical SAM Methyltransferase Catalyzing Non-radical Reactions

B₁₂-dependent radical SAM enzymes are an emerging enzyme family with approximately 200,000 proteins. These enzymes have been shown to catalyze chemically challenging reactions such as methyl transfer to sp2- and sp3-hybridized carbon atoms. However, to date we have little information regarding their complex mechanisms and their biosynthetic potential. Here we show, using X-ray absorption spectroscopy, mutagenesis and synthetic probes that the vitamin B₁₂-dependent radical SAM enzyme TsrM catalyzes not only C- but also N-methyl transfer reactions further expanding its synthetic versatility. We also demonstrate that TsrM has the unique ability to directly transfer a methyl group to the benzyl core of tryptophan, including the least reactive position C4. Collectively, our study supports that TsrM catalyzes non-radical reactions and establishes the usefulness of radical SAM enzymes for novel biosynthetic schemes including serial alkylation reactions at particularly inert C−H bonds.     

可见光引发的氧自由基的新型产生方式及反应

羧酸自由基及烷氧自由基等氧自由基是有机合成中的重要中间体,近些年通过可见光引发的氧化还原反应产生此类自由基的研究取得重要进展.本综述文章将聚焦于羧酸衍生物及羧酸作为羧酸自由基前体,醇衍生物及醇作为烷氧自由基前体,在光催化氧化还原条件下发生单电子转移产生氧自由基的新型方式,并将简单介绍其后续反应.     

Expanding the Chemistry of the Class C Radical SAM Methyltransferase NosN by Using an Allyl Analogue of SAM

The radical S‐adenosylmethionine (SAM) superfamily enzymes cleave SAM reductively to generate a highly reactive 5′‐deoxyadenosyl (dAdo) radical, which initiates remarkably diverse reactions. Unlike most radical SAM enzymes, the class C radical SAM methyltransferase NosN binds two SAMs in the active site, using one SAM to produce a dAdo radical and the second as a methyl donor. Here, we report a mechanistic investigation of NosN in which an allyl analogue of SAM (allyl‐SAM) was used. We show that NosN cleaves allyl‐SAM efficiently and the resulting dAdo radical can be captured by the olefin moieties of allyl‐SAM or 5′‐allylthioadenosine (ATA), the latter being a derivative of allyl‐SAM. Remarkably, we found that NosN produced two distinct sets of products in the presence and absence of the methyl acceptor substrate, thus suggesting substrate‐triggered production of ATA from allyl‐SAM. We also show that NosN produces S‐adenosylhomocysteine from 5′‐thioadenosine and homoserine lactone. These results support the idea that 5′‐methylthioadenosine is the direct methyl donor in NosN reactions, and demonstrate great potential to modulate radical SAM enzymes for novel catalytic activities.     

Radical chain reactions using THP as a solvent

THP (tetrahydropyran) has been found to show an excellent stability towards autooxidation, compared with THF. Tributyltin hydride mediated radical cyclization, when conducted in THF as a solvent, suffers from competition of hydrogen abstraction from the solvent, whereas the use of THP resulted in the course to negligible degree. Tributyltin hydride, TTMSS, and hexanethiol mediated radical reactions were carried out successfully using THP as a solvent.     

Hydrogen radical and hydroxyl radical hydrogen abstraction reaction from formyl fluoride studied with hybrid density functional theory methods

With the goal of reducing flame velocity in combustion reactions, this study focused on the conversion of hydrogen and hydroxyl radicals into relatively unreactive hydrogen and water molecules through the inter-conversion of formyl fluoride to fluoroformyl radicals. Hybrid DFT computational methods were employed to confirm these results. Based on this, the fluoroformyl radical-assisted transformation of the hydrogen and hydroxyl radicals into hydrogen and water molecules was discussed.     

Rapid-Scan Electron Paramagnetic Resonance of Highly Resolved Hyperfine Lines in Organic Radicals.

X-band (ca. 9 GHz) fluid solution rapid-scan electron paramagnetic resonance spectra are reported for radicals with multiline spectra and resolution of hyperfine lines as narrow as 30 mG. Highly-resolved spectra of 3-carbamoyl-2,2,5,5-tetramethylpyrrolidin-1-yloxy, diphenylnitroxide, galvinoxyl, and perylene cation radical with excellent signal-to-noise are shown, demonstrating the capabilities of the rapid-scan technique to characterize very small, well-resolved hyperfine couplings. To acquire high resolution spectra the signal bandwidth must be less than the resonator bandwidth. Signal bandwidth is inversely proportional to linewidth and proportional to scan rate. Resonator bandwidth is inversely proportional to resonator Q. Proper selection of scan rate and resonator Q is needed to achieve resolution of closely-spaced narrow EPR lines.     

EPR Studies of (3, 5-di-t-Butyl-0-Benzoquinone) Tetracarbonylrhenium(0) Radical

The organometallic radical: (3,5-di-t-butyl-0-benzoquinone)tetracarbonyl-rhenium(0) and its triphenylphosphine substituted derivatives were studied by EPR spectroscopy. The unpaired electron is shown to be localized in the organic 1,2-diketone ligand. The rate of carbonyl substitution by triphenylphosphine at the unsubstituted rhenium radical indicates a second order reaction. The activation parameters are ΔH* =19.1±0.8Kcal/mole and ΔS*-3.0±1.5 eu/mole.     

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.     

Electrochemical Amination: Efficiency of a Radical Substitution

Electrochemical amination of benzene in sulfuric acid electrolytes is studied and experimental conditions for highly efficient synthesis of primary aromatic amino compounds are determined. In the electrolysis of Ti(IV)–NH₂OH–C₆H₆ in 11 M H₂SO₄ solutions containing acetic acid or acetonitrile as organic solvents, aniline and isomeric phenylenediamines are obtained with the total yields by hydroxylamine of 95.6 and 99.6%, respectively. A monoamino compound is the main product of radical substitution in acidic organo-aqueous media. It is found that the use of acetonitrile in electrochemical process is limited to certain sulfuric acid concentrations and temperatures.     

Si-H, P-H 和 S-H 键离解能Alfa取代基效应研究

CBS-Q and G3 methods were used to generate a large number of reliable Si--H, P---H and S--H bond dissociation energies （BDEs） for the first time. It was found that the Si--H BDE displayed dramatically different substituent effects compared with the C--H BDE. On the other hand, the P---H and S--H BDE exhibited patterns of substituent effects similar to those of the N--H and O--H BDE. Further analysis indicated that increasing the positive charge on Si of XSiH3 would strengthen the Si--H bond whereas increasing the positive charge on P and S of XPH2 and XSH would weaken the P---H and S--H bonds. Meanwhile, increasing the positive charge on Si of XSiH2^＋ stabilized the silyl radical whereas increasing the positive charge on P and S in XPH＂ and XS＊ destabilized P- and S-centered radicals. These behaviors could be reasonalized by the fact that Si is less electronegative than H while P and S are not. Finally, it was demonstrated that the spin-delocalization effect was valid for the Si-, P- and S-centered radicals.     

聚合反应中非等活性初级自由基的终止问题

许多光(热)引发剂能分解成二个非等活性自由基。根据非等活性初级自由基终止的概念,可导出以下方程:以ln(R_p~2/[I][M]对R_p/[M]~2作图,发现在很大的引发剂浓度范围内都较好地反映出非等活性初级自由基终止对聚合反应的贡献。对于安息香和O-酰基-α-酮肟类光引发剂,当它们的浓度大于1.0×10~(-2)(mol·1~(-1)时,聚合反应体系中明显存在非等活性初级自由基终止反应。随着反应体系的温度增加,终止反应程度相对减少,说明E_(prt)—E_i—E_p<0,对于O-酰基酮肟和双(O-酰基)-(α,β-二肟-三乙胺光引发体系,在引发剂浓度很低时,也存在初级自由基终止反应。自由基越稳定,初级自由基终止反应影响越明显。     

原子转移自由基聚合及可控自由基聚合

以作者在原子转移自由基聚合领域的研究成果为主导,结合国内外文献,对近年来出现的颇具影响的可控自由基聚合体系与进行了评述与展望。     

乙烯基自由基(C2H·3)与羟基自由基(OH·)反应势能面的理论研究

在QCISD（T）/6-311G（2df,p)//B3LYP/6-311G（d,p)水平上对自由基反应C2H3^. OH^.进行了计算，结果表明，经过缔合、多步H转移、CH3转移和离解等复杂过程，最终要得到8种产物（P1-P8），茯中产物P2（H2CCO H2）和P6（CH3CO^. H^.）是主要产物。本文得到的CH2CHOH（1或1‘），CH3CHO（2）和CH3COH（3）之间的过渡态TS1/2，TS1‘/3和TS2/3的能量顺序与Wesdemiotis等的实验推测相反，而与Smith等的计算结果一致。     

Radical dearomatising spirocyclisations onto the C-2 position of benzofuran and indole

Spirolactams were obtained via an intramolecular radical ipso-type spirocyclisation in benzofuran and indole systems. Alkyl, vinyl and aryl radicals, tethered at the C-2 position of the heterocycle underwent radical cyclisation to produce novel tricyclic partially dearomatised heterocycles in moderate yields. Fragmentation of the furan ring was observed subsequent to spirocyclisation of a vinyl radical onto a benzofuran.