光化学中的离子型反应机理

光化学反应机理模式的概述光化学是研究电子重新分布的所谓电子激发态分子反应的。光化学反应是与同时发生的物理现象,即光物理,例如,光的辐射和吸收、热量的变化等密切相关。现代光化学反应机理的研究发展了化学反应性及结构理论的基本概念。这使实验化学家们可以用描述基态反应中电子移动方     

微反应器中的不对称光化学反应

化学反应的手性诱导一直备受化学家的关注,虽然不对称热化学合成和手性技术已经取得了巨大的进展,但不对称光化学反应的研究远远没有取得相应的成功.激发态寿命短、活化能低是导致其对映选择性低的主要原因.最新的研究表明,采用含手性空间或经手性修饰的微环境可以使光化学反应的立体选择性大大提高.本文针对这一热点问题,综述在微反应器中进行不对称光化学反应的研究进展.     

微反应器控制的化学反应的选择性

研究利用分子筛、Nafion薄膜、低密度聚乙烯薄膜和囊泡作为微反应器控制有机光化学反应的方向,提高反应的选择性和可能性.在NaY沸石或低密度聚乙烯薄膜中,带有长烷基链或醚链的二芳基化合物光二聚只生成分子内的加成产物,而不生成分子间的加成产物,从而在底物浓度很大的情况下,高选择性地合成了大环化合物.通过控制底物和敏化剂分子在ZSM-5沸石、Nafion薄膜和囊泡中的分布高选择性地控制烯烃光敏氧化反应的方向,单一地生成单重态氧的氧化产物或超氧负离子的氧化产物.利用Nafion薄膜作为介质进行光诱导电子转移,得到超长寿命的电荷分离态.     

正戊烷与SO2气相光化学反应自由基机理的ESR验证

烷烃与SO2的气相光化学作用为自由基反应[1].Penzhorn等[2]对C4以下的气相烷烃与SO2光化学反应产物的复杂性和多样性进行了推测,此后对该光化学反应机理的研究均以反应产物(特别是凝聚态产物)为基础进行的[3].为验证烷烃与SO2光化学反应体系中确实存在自由基,Makarov等[4]向正戊烷与SOz光化学反应体系中引入NO,通过对反应起始阶段的产物的光谱分析和反应动力学研究,论证了该反应的自由基过程.ESR技术是检测自由基的有效方法,Stokes等[5]利用自旋捕集-ESR技术成功地测得了气相羟基自由基的存在.     

有机聚合物材料表面受限光感应C–H键转换反应研究进展

有机聚合物材料普遍具有表面能低和反应惰性的特点,限制了其在光、电、分离、生物医用等高端领域的应用.表面改性是有机高分子材料高性能化的重要手段,其涉及的核心科学问题是表面C–H键的活化/转换化学.光化学反应具有快速高效、化学选择性高、环境友好、可低温反应、时间/空间精确可控等特点,在有机聚合物材料表面改性上具有突出优势.本文介绍了本课题组多年来在有机聚合物材料表面受限光感应C–H键转换反应方面的研究进展,系统介绍了此类反应的机理,以及在生长/固定无机、导电材料、生物分子等方面的应用,并展望了光感应C–H键转换反应今后的发展方向.     

蒽衍生物的光化学[4+4]二聚反应:近期合成进展与应用

蒽及其衍生物的[4+4]光二聚反应已有超过百年的研究历史.该经典光化学反应具有底物多样、操作简便、(可控条件下)可逆等突出优点,然而其反应产物的异构体分离困难和溶解度差等制约因素限制了该反应在合成化学中的应用.鉴于反应的二聚体产物具有独特的分子刚性和几何形状,其尚未被充分挖掘的合成用途值得深入研究.总结本世纪十余年来蒽衍生物光二聚反应的代表性研究成果,分别围绕反应区域选择性和对映选择性的合成进展、在功能有机分子和分子机器领域的合成应用进行介绍.     

光化学反应的极谱法研究及应用

光化学反应的极谱法研究及应用蒋治良，王盛杰（广西师范大学计算分析测试中心，桂林５４１００４）光化学反应的极谱分析法系基于物质吸收了紫外－可见辐射能而引起诸如光分解、光加成、光氧化还原及光异构等光化学反应，导致物质的结构或性质发生了某些变化，诸如形成了...     

有机化学新领域──固态光化学的研究

介绍了有机化学新领域──固相光化学研究的重要意义和特点。通过色氨酸类、核酸碱基衍生物同稠环化合物异种分子间固态光化学的研究，揭示出这种反应的高选择性和专一性，对反应历程也进行了初步研究，为合成化学提供了新方法。利用晶格控制物质，使不易进行光化学反应的物质可顺利地定向进行光化学反应，亦可直接用于合成Ｄ或Ｌ手性化合物，省去拆分。对Ｃ－Ｔ络合物（电荷转移）和分子化合物的固态光化学也进行了研究。     

基于环糊精的超分子手性光化学反应

总结了以环糊精为手性主体分子的超分子手性光化学反应及其特点,内容包括单分子手性光化学反应、双分子手性光化学反应、手性光催化反应以及手性光反应中的波长效应等四个方面.着重总结了环糊精对不同光反应底物的包结特性,天然和化学修饰的环糊精分子对反应速度、产物的分布和反应选择性的影响以及其作用机理.探讨了环糊精作为主体分子用于手性光化学反应所独具的优点,总结了现阶段研究中存在的问题,并对该方面工作的发展进行了展望.     

有机化学新领域—固态化学的研究

介绍了有机化学新领域－固相光化学研究的重要意义的特点。通过色氨酸类、核酸碱基衍生物同稠环化合物异种分子间固态光化学的研究。提示出这种反应的高选择性和专一性。对反应历程也进行了初步研究。为合成化学提供了新方法。利用晶格控制物质，使不易进行光化学反应的物质可顺利地定向进行光化学反应，亦可直接用于合成Ｄ或Ｌ手性化合物，省去拆分。对Ｃ－Ｔ络合物（电荷转移）和分子化合物的固态化学也进行了研究。     

超分子体系中的光物理和光化学过程

总结了我们组近几年来对超分子体系中的光物理和光化学过程所做的工作,包括三个部分：(1)微反应器控制的有机光化学反应的选择性,(2)疏水、疏脂作用对光物理和光化学过程的影响,(3)超分子体系中的电子转移、能量传递和光化学转换。     

微环境条件影响的光化学反应研究进展

对近年来微环境条件影响的光反应化学反应研究和一综合评述，包括主体－客体络合物，晶格控制物Ｌｅｗｉｓ酸络合物，电荷转移络合物，胶束以及吸附在硅胶或分子筛表面等体系光化学反应方面取得的重要成果，这类微环境条件影响的光化学反应具有较高的选择性和专一性，参考文献１５篇。     

Overlap of colloid chemistry and photochemistry in surfactant systems

Interactions of organic photochemistry and colloid chemistry in surfactant systems can be divided in two distinct sections: (i) influences of the colloids on photochemical reactions and (ii) influences of photochemical reactions on macroscopic properties of colloidal surfactant systems. As to (i), the (generally poor) selectivity of photochemical reactions can be improved by performing the reactions in systems containing surfactant aggregates. Regioselectivity, stereoselectivity and multiplicity selectivity can be directed. As to (ii), in lyotropic liquid crystalline systems the solubilization of certain aromatic compounds specifically changes phase transition temperatures. Upon photochemically transforming such solubilizates in situ isothermal phase transitions can be brought about, provided that photoeducts and photoproducts induce distinct transition temperatures. Similarly in dilute surfactant systems solubilizates specifically affect size and shape of micellar aggregates, so that changes in flow behaviour take place, which can be switched via photochemical transformation of solubilizates. Possible exploitations of the effects are discussed and compared with the application of similar effects in related non-surfactant systems, with emphasis on photochemical information storage.     

Synthesis of seven and higher membered nitrogen containing heterocycles using photochemical irradiation

Photochemical reactions have been applied for the synthesis of complex targets in many examples recently. In many cases, these processes provide access to unique modes of reactivity or offer unrivaled increases in molecular complexity. The key-features of photochemical reactions include increased selectivity, conversion, and yield and are beneficial for industrial and “green” processes. Despite these advantages, however, photochemical reactions in chemical production or R and D processes are rare. Most technical processes are limited to commodity chemicals and have been developed decades ago. The application of photochemical reactions for the synthesis of fine chemicals, natural products, and pharmaceutically active compounds, has become very popular. Photochemical reactions are used for organic synthesis and this review article highlighted the syntheses of heterocycles. Photochemistry is particularly fascinating and afforded an exotic charm due to its unconventional nature. In this review, I have given a clear idea of applicability of photochemical irradiations for the synthesis of a number of seven and higher membered N-heterocycles.     

Alkali ion exchanged Nafion as a confining medium for photochemical reactions

Methanol-swollen Nafion beads were used as microreactors to control the photochemical reaction pathways. Product selectivity in three unimolecular reactions, namely, the photo-Fries rearrangement of naphthyl esters, Norrish Type I reaction of 1-phenyl-3-p-tolyl-propan-2-one and Norrish Type I and Type II reactions of benzoin alkyl ethers were examined. The influence of cations over the photodimerization of acenaphthylene and cross-photodimerization between acenaphthylene and N-benzyl maleimide included within Nafion were also examined. The photochemical behaviors of the above substrates were significantly altered within Nafion compared with their solution photochemistry. Of particular interest, the product distributions were found to depend on the counter cations of Nafion.     

Flow-Injection Analysis of Pharmaceuticals

The current state and outlooks of the development of the flow-injection analysis of medicinal substances in pharmaceuticals and biological fluids are considered. The role of chemical, photochemical and enzymatic reactions of derivatization in the flow-injection determination of pharmaceuticals is outlined. The role of detection methods in improving the selectivity and sensitivity of the flow-injection analysis of pharmaceuticals and expanding its possibilities in pharmaceutical analysis is considered     

Engineering reactions in crystalline solids: photochemical generation of secondary and tertiary enol radical pairs from crystalline ketodiesters.

The photochemical decarbonylation of several crystalline 1,3-acetonedicarboxylates has been analyzed in solution and in the solid state. It is shown that the efficiency of the solid-state reaction depends on the stability of the intermediate acyl-alkyl and alkyl-alkyl radical pairs. Reactions proceeding through tertiary enol radicals are more efficient than reactions proceeding through secondary enol radical centers. Solid-state reactions that require the intermediacy of primary enol radicals do not occur. It is also shown that the selectivity of product formation in crystals depends on the structure of the reactant solid phase.     

Recent advance of cyclodextrins as nanoreactors in various organic reactions: a brief overview

Cyclodextrins have been widely used in organic syntheses, which can bind substrates and catalyze chemical reactions with high selectivity as well as transfer hydrophobic molecules into environmental friendly medium by supramolecular interaction through reversible formation of host–guest complexes. Herein we provide an overview of the recent developments of native and modified cyclodextrins as catalyst in several reactions. These reactions are classified into twelve types involving oxidation, reduction, addition, Tsuji-Trost reaction, cyclization, protection, bromination, coupling, oxygen–sulfur exchange, ring-opening, hydrolysis and photochemical reaction.     

Enhancing Selectivity and Kinetics in Oxidative Photocyclization by Supramolecular Control

Photochemical reactions typically proceed via multiple reaction pathways, yielding a variety of isomers and products. Enhancing the selectivity is challenging. Now, the potential of supramolecular control for oxidative photocyclization of a tetraarylethylene, containing a stereogenic ?C=C? bond, is demonstrated. In solution, this photochemical reaction produces three constitutional isomers (substituted phenanthrenes), with slow kinetics. When the reactant is assembled into a crystalline framework, only one product forms with accelerated kinetics. Key to this selectivity enhancement is the integration into a surface grown metal–organic framework (SURMOF); the dramatic gain in selectivity is ascribed to the hindrance of the rotational freedom of the ?C=C? double bond. The structure of the MOF is key; the corresponding reaction in the solid does not result in such a high increase in selectivity. A striking change of luminescence properties after photocyclization is observed.     

The Power of Action Plots: Unveiling Reaction Selectivity of Light-Stabilized Dynamic Covalent Chemistry

Exploiting the optimum wavelength of reactivity for efficient photochemical reactions has been well-established based on the development of photochemical action plots. We herein demonstrate the power of such action plots by a remarkable example of the wavelength-resolved photochemistry of two triazolinedione (TAD) substrates, i.e., aliphatic and aromatic substituted, that exhibit near identical absorption spectra yet possess vastly disparate photoreactivity. We present our findings in carefully recorded action plots, from which reaction selectivity is identified. The profound difference in photoreactivity is exploited by designing a ‘hybrid’ bisfunctional TAD molecule, enabling the formation of a dual-gated reaction manifold that demonstrates the exceptional and site-selective (photo)chemical behavior of both TAD substrates within a single small molecule.