芳香酮、酚、胺、羧酸及含氮杂环的解离常数与其π电子分布的关系

本文用微扰分子轨道(PMO),Hackel分子轨道(HMO)和自洽场分子轨道(PPP)方法研究了芳香酮、芳香胺、酚和含氮杂环等化合物的解离常数(pK_α)和π-电子分布的关系。结果表明对交替烃,PMO,HMO和PPP在某些情况下,有类似的平行结果。pK_α与活性原子上的电荷密度q_w有着良好的线性关系。但对芳香甲酸和含氮杂环,pK_α与q_x有反比关系。对芳香甲酸pK_α主要由偶极矩决定。而含氮杂环主要由氮原子中的孤对电子与最高充满轨道中的电子间的排斥积分所控制。     

顺反异构的转化与应用

作为立体化学的一部分，顺反异构反应是一类重要的有机反应。在其教学过程中，对顺反异构体间性质和结构变化的讲解，有助于学生理解顺反异构现象。从介绍偶氮苯分子、共轭多烯分子和芳香亚胺分子的顺反异构在如分子马达等领域的应用，增强学生学习该部分知识的兴趣，了解有机化学的发展。     

过渡金属催化的芳香化合物三氟甲基化研究进展

向芳香化合物分子中引入三氟甲基在制药,农用化学品和有机材料的砌块合成中有重大的意义.由于过渡金属催化的反应反应条件温和,底物适用性广等优点,最近几年,逐渐被科学家应用到芳香化合物的三氟甲基化中,成为追捧的热点.综述了近几年在利用过渡金属对芳香化合物进行的三氟甲基化中取得的重大进展.     

过渡金属催化芳香胺中性碳氮键活化与转化反应新进展

C–N键广泛存在于有机小分子、生物大分子及药物分子中。芳香胺是天然产物和药物分子之中的重要结构单元,通过对芳香胺芳基C–N键的断裂实现其催化转化,可作为药物分子后期修饰的重要手段。我们在此综述了过渡金属催化的芳香胺中性芳基C–N键断裂转化反应的最新研究进展,并对芳香胺芳基C–N键活化的发展趋势进行了展望。     

环芳有机分子中分子轨道的通过空间相互作用

本文给出了描述环芳类化合物分子轨道通过空间相互作用的模型, 进一步采用离散变分X~α自洽场方法研究它们的电子结构, 并计算三类环芳有机分子轨道的通过空间相互作用, 计算结果表明环芳类有机分子的通过空间相互作用的大小随分子中苯环, 乙炔、乙烯间距离的增大而衰减, 本文的结果与定性分析是一致的。     

芳香偶氮衍生物合成策略研究的新进展

芳香偶氮化合物具有独特的光致顺反异构特性,不仅应广泛用于传统化学工业,还将应用于光化学分子开关、主客体超分子化学识别、自组装液晶材料、生物医学成像与化学分析以及光驱分子马达等诸多新兴科学领域.特别具挑战性的是开发具有高化学稳定性和热稳定性又易检测的偶氮发色团,近年来受到科研工作者们的高度关注.随着人们对研究新型芳香偶氮衍生物的迫切需要,又相继创新和发展了一些更新、更有效的芳香偶氮化合物合成方法,综述了最近新型芳香偶氮衍生物合成方法的新进展,尤其强调了芳基肼的氧化脱氢反应和金属催化偶联反应、芳胺的氧化反应、硝基芳香化合物的还原偶联反应、芳香偶氮氧化物的转化与还原、叠氮芳香化合物的催化偶联与热分解反应以及芳香基重氮盐的偶合与催化偶联反应等在芳香偶氮化合物合成方面应用的新趋势.     

六钼酸根的单取代芳香亚胺衍生物的合成与结构

多酸亚胺衍生物是构造新型有机/无机杂化的纳米结构材料的重要分子构件,在多酸有机衍生物化学、多酸超分子化学与多酸材料化学中具有极其重要的地位[1,2].但是有关多酸有机亚胺衍生物的合成化学方面的研究还比较少见[3].最近我们在DCC脱水法的基础上,以八钼酸根和芳香伯胺为原料,芳香伯胺的共轭酸作为催化剂,发展了制备六钼酸根的单取代芳香亚胺衍生物的新的合成化学方法(见图1)[4].该方法不仅反应条件温和(可以在室温下进行),而且反应时间短(不超过6 h)、收率合适(约50%)、易于操作.特别是采用该方法可以方便地得到芳环上含溴、氯或硝基等吸电子取代基的衍生物,而采用文献方法则不易或不能制备与纯化这类衍生物.这样的衍生物因含有反应活性的官能团,可以作为分子基元,用于构建新奇的有机/无机杂化的分子材料[5].     

蓝光萘酰亚胺发光材料的合成与表征

通过在4位引入不同芳香基团,采用Suzuki和Stille偶联反应,设计与合成了一系列新型1,8-萘酰亚胺类荧光染料,并研究了它们的紫外-可见吸收、荧光发射和电化学行为等光物理性质。这些化合物在甲苯中均发射蓝色荧光,最大吸收和荧光发射峰分别在357～378和423～451nm之间,且随着芳香基团供电性增强,吸收和荧光发射波长发生红移。芳香基团的结构对化合物的发光效率影响很大,其中,取代基为甲氧基苯的化合物具有最高的荧光量子效率,可达0.98,而取代基为噻吩的化合物荧光量子效率最低,只有0.17。电化学循环伏安研究表明该类化合物具有较高的电子亲合力,不同芳香基团的引入只影响化合物的被占分子轨道(HOMO)能级,而对化合物的最低空分子轨道(LUMO)能级没有影响,即LUMO能级由1,8-萘酰亚胺单元决定。     

芳香胺类化合物的二氟烷基化研究进展

含氟化合物具有独特的物理化学特性，被广泛应用于药物开发、临床医学、农业化学、材料科学和有机合成等领域。过去几十年里，利用含氟砌块策略将含氟官能团引入有机分子中引起了合成化学家们的广泛关注，特别是利用二氟烷基化试剂合成具有重要价值的含氟分子方面取得了重要进展。本文聚焦于总结芳香胺类化合物的二氟烷基化反应，按照金属催化、可见光催化以及其它方法对近年来文献报道的芳香氮杂化合物的二氟烷基化反应进行介绍，并对反应机理进行探究，期望为该类含氟化合物的合成及进一步应用提供方法和思路。     

基于二酮基吡咯并吡咯的π-共轭分子的有机太阳能电池给体材料的设计与理论研究

本文设计了系列基于二酮基吡咯并吡咯(DPP)的有机小分子太阳能电池(OSCs)给体材料.设计的分子结构中，2个DPP分子片段作为2个端基通过不同的芳香杂环π-桥相连接.利用密度泛函理论和含时密度泛函理论方法研究了所设计化合物的电子和光学性质.研究结果表明，在分子中引入不同的π-桥可以有效调节设计分子的前线分子轨道能量、能隙和吸收光谱，但是对几何结构影响很小.所设计化合物1-8均在近红外光谱区具有强吸收和窄能隙，这有利于提高有机太阳能电池的短路电流和光吸收效率.前线分子轨道分析发现，化合物1-8具有较低的最高占据轨道能级，可提高有机太阳能电池的开路电压.化合物1-3,5和7的前线分子轨道能级与典型富勒烯受体材料相匹配，可选用PCBM,bisPCBM和PC₇₁BM作为受体材料；而化合物4,6和8则应考虑选用其他的太阳能电池受体材料.结果表明，所设计的分子可作为性能优良的OSCs给体材料，为开发和利用太阳能电池给体材料提供理论依据.     

Transient bonds and chemical reactivity of molecules

Electron delocalization between the reagent and reactant molecules is the principal driving force of chemical reactions. It brings about the formation of new bonds and the cleavage of old bonds. By taking the aromatic substitution reaction as an example, we have shown the orbitals participating in electron delocalization. The interacting orbitals obtained are localized around the reaction sites, showing the chemical bonds that should be generated and broken transiently along the reaction path. By projecting a reference orbital function that has been chosen to specify the bond being formed on to the MOs of the reactant molecules, the reactive orbitals that are very similar to the interacting orbital have been obtained. The local potential of the reaction site for electron donation estimated for substituted benzene molecules by using these projected orbitals shows a fair correlation with the experimental scale of the electron-donating and -withdrawing strength of substituent groups. The reactivity is shown to be governed by local electronegativity and local chemical hardness and also by the localizability of interaction on the reaction site. © 1996 John Wiley & Sons, Inc.     

Reactive orbital energy theory serving a theoretical foundation for the electronic theory of organic chemistry

It is established that the reactive orbital energy theory (ROET) theoretically reproduces the rule-based electronic theory diagrams of organic chemistry by a comparative study on the charge transfer natures of typical organic carbon–carbon and carbon–heteroatom bond formation reactions: aldol, Mannich, α-aminooxylation, and isogyric reactions. The ROET, which is an expansion of the reaction electronic theories (e.g., the frontier orbital theory) in terms of orbital energies, elucidates the reactive orbitals driving reactions and the charge transferability indices of the reactions. Performing the ROET analyses of these reactions shows that the charge transfer directions given in the rule-based diagrams of the electronic theory are reproduced even for the functional groups of charge transfer destinations in all but only two processes for 38 reaction processes. The ROET analyses also make clear the detailed orbital-based pictures of these bond formation reactions: that is, the use of the out-of-plane antibonding π orbitals in acidic conditions (enol-mode) and in-plane antibonding π orbitals in basic conditions (enolate-mode), which explain the experimentally assumed mechanisms such as the π-bond formations in acidic conditions and σ-bond formations at α-carbons in basic conditions. Furthermore, the ROET analyses explicate that the methyl group initially accepts electrons and then donates them to the bond formations in the target reactions. It is, consequently, suggested that the ROET serves a theoretical foundation for the electronic theory of organic chemistry.     

Coordination and haptotropic migration of Cr(CO)3 in polycyclic aromatic hydrocarbons: the effect of the size and the curvature of the substrate

In this work, we study the reaction mechanism of the tricarbonylchromium complex haptotropic rearrangement between two six-membered rings arranged like in naphthalene of four polycyclic aromatic hydrocarbons (PAHs). It has been found that the reaction mechanism of this haptotropic migration can either occur in a single step or stepwise depending on the interaction between the orbitals of the Cr(CO)3 and the PAH fragments. Our results show that the size of the cyclic system favors the metal migration whereas the curvature of the organic substrate tends to slow down the rearrangement. We discuss the key factors that help to explain this behavior through orbital and energy decomposition analysis.     

How Alkali Cations Catalyze Aromatic Diels‐Alder Reactions

We have quantum chemically studied alkali cation‐catalyzed aromatic Diels‐Alder reactions between benzene and acetylene forming barrelene using relativistic, dispersion‐corrected density functional theory. The alkali cation‐catalyzed aromatic Diels‐Alder reactions are accelerated by up to 5 orders of magnitude relative to the uncatalyzed reaction and the reaction barrier increases along the series Li⁺ < Na⁺ < K⁺ < Rb⁺ < Cs⁺ < none. Our detailed activation strain and molecular‐orbital bonding analyses reveal that the alkali cations lower the aromatic Diels‐Alder reaction barrier by reducing the Pauli repulsion between the closed‐shell filled orbitals of the dienophile and the aromatic diene. We argue that such Pauli mechanism behind Lewis‐acid catalysis is a more general phenomenon. Also, our results may be of direct importance for a more complete understanding of the network of competing mechanisms towards the formation of polycyclic aromatic hydrocarbons (PAHs) in an astrochemical context.     

Orbital views of molecular conductance perturbed by anchor units

Site-specific electron transport phenomena through benzene and benzenedithiol derivatives are discussed on the basis of a qualitative Hu?ckel molecular orbital analysis for better understanding of the effect of anchoring sulfur atoms. A recent work for the orbital control of electron transport through aromatic hydrocarbons provided an important concept for the design of high-conductance connections of a molecule with anchoring atoms. In this work the origin of the frontier orbitals of benzenedithiol derivatives, the effect of the sulfur atoms on the orbitals and on the electron transport properties, and the applicability of the theoretical concept on aromatic hydrocarbons with the anchoring units are studied. The results demonstrate that the orbital view predictions are applicable to molecules perturbed by the anchoring units. The electron transport properties of benzene are found to be qualitatively consistent with those of benzenedithiol with respect to the site dependence. To verify the result of the Hu?ckel molecular orbital calculations, fragment molecular orbital analyses with the extended Hu?ckel molecular orbital theory and electron transport calculations with density functional theory are performed. Calculated results are in good agreement with the orbital interaction analysis. The phase, amplitude, and spatial distribution of the frontier orbitals play an essential role in the design of the electron transport properties through aromatic hydrocarbons.     

Orbital phase in Suzuki–Miyaura cross-coupling reactions

We investigated the electronic structures of the transition states of the oxidative addition, transmetalation, and reductive elimination steps in the catalytic cycle of the title reaction. The frontier orbital theory was surprisingly found to be applicable whereas any d orbitals of transition metals can be a main component of frontier orbitals because of their close energies. Visualizing the actually calculated HOMO and LUMO of the two parts of the transition structure of each step clearly demonstrated their orbital phase matching in favor of overlapping. The HOMO for the transmetalation step suggests that electron-donating ability of the carbon–metal bond of organometallic compounds (RMX) could control the reactivities of related cross-coupling reactions. The energies of the molecular orbitals having large amplitudes of the C–M bonding orbitals of RMX explain why the Suzuki–Miyaura cross-coupling reaction needs a base while the Kumada–Tamao and Negishi reactions take place without any bases.     

Orbital signatures of methyl in L-alanine

Molecular orbital signatures of the methyl substituent in L-alanine have been identified with respect to those of glycine from information obtained in coordinate and momentum space, using dual space analysis. Electronic structural information in coordinate space is obtained using ab initio (MP2/TZVP) and density functional theory (B3LYP/TZVP) methods, from which the Dyson orbitals are simulated based on the plane wave impulse approximation into momentum space. In comparison to glycine, relaxation in geometry and valence orbitals in L-alanine is found as a result of the attachment of the methyl group. Five orbitals rather than four orbitals are identified as methyl signatures. That is, orbital 6a in the core shell, orbitals 11a and 12a in the inner valence shell, and orbitals 19a and 20a in the outer valence shell. In the inner valence shell, the attachment of methyl to glycine causes a splitting of its orbital 10a' into orbitals 11a and 12a of L-alanine, whereas in the outer valence shell the methyl group results in an insertion of an additional orbital pair of 19a and 20a. The frontier molecular orbitals, 24a and 23a, are found without any significant role in the methylation of glycine.