电子效应对单取代苯定位效应和反应活性的影响

单取代苯的定位效应和反应活性主要受取代基的电子效应控制,列表总结了取代基的电子效应与定位效应和反应活性的关系,分析了烃基电子效应的特殊性,取代基具有-Ⅰ效应的普遍性。除卤素取代基外,探讨了共轭效应的方向对定位效应和反应活性的决定作用。     

α-Fe2O3掺杂对In2O3电导和气敏性能的影响

用化学共沉淀法制备了α Fe2O3掺杂的In2O3纳米晶微粉,研究了α Fe2O3掺杂对In2O3电导和气敏性能的影响. 结果表明, α Fe2O3和In2O3间可形成有限固溶体In2－xFexO3(0≤x≤0.40); Fe3＋对In2O3晶格中In3＋格位的部分取代,大大增强了阴阳离子间的结合力,导致材料中氧空位VO×数骤降、 自由电子的浓度变稀和电导下降. n(Fe3＋):n(In3＋)=5 :5的共沉淀粉于800 ℃下灼烧4 h所得的α Fe2O3掺杂In2O3传感器元件,对45 μmol•L－1 C2H5OH的灵敏度达54.0,为相同浓度干扰气体汽油的8倍多.     

beta-Hydrogen Kinetic Effect

A combined kinetic and DFT study of the uncatalyzed isomerization of cationic solvent complexes of the type cis-[Pt(R')(S)(PR3)2]+ (R' = linear and branched alkyls or aryls and S = solvents) to their trans isomers has shown that the reaction goes through the rate-determining dissociative loss of the weakly bonded molecule of the solvent and the interconversion of two geometrically distinct T-shaped 14-electron three-coordinate intermediates. The Pt-S dissociation energy is strongly dependent on the coordinating properties of S and independent of the nature of R'. The energy barrier for the fluxional motion of [Pt(R')(PR3)2]+ is comparatively much lower ( approximately 8-21 kJ mol-1). The presence of beta-hydrogens on the alkyl chain (R' = Et, Prn, and Bun) produces a great acceleration of the reaction rate. This accelerating effect has been defined as the beta-hydrogen kinetic effect, and it is a consequence of the stabilization of the transition state and of the cis-like three-coordinate [Pt(R')(PR3)2]+ intermediate through an incipient agostic interaction. The DFT optimization of [Pt(R')(PMe3)2]+ (R' = Et, Prn, and Bun) reproduces a classical dihapto Pt....eta2-HC agostic mode between the unsaturated metal and a dangling C-H bond. The value of the agostic stabilization energy (in the range of approximately 21-33 kJ mol-1) was estimated by both kinetic and computational data and resulted in being independent of the length of the hydrocarbon chain of the organic moiety. A better understanding of such interactions in elusive reaction intermediates is of primary importance in the control of reaction pathways, especially for alkane activation by metal complexes.     

高分子效应

用许多杰出的实例,从高分子骨架的机械支架作用、邻基效应、协同效应、模板聚合等诸方面探论了高分子效应。     

螺共轭效应及其应用

螺共轭术语是1967年由Simmons和Fukunaga首次提出的, 由于其特殊的立体电子效应而引起了科学家们的广泛关注. 综述了40年来有关螺共轭的理论发展以及在发光材料、光致变色材料、非线性光学材料、螺环染料、有机导体等方面的研究现状, 展望了螺共轭效应的应用前景, 并提出了一些新的设想.     

同位素效应简介

对同位素效应的类别、特征、原理、在研究反应机理中的意义以及同位素效应发展的最新动态进行简单介绍 ;讨论了同位素效应应用于生物化学中的一些反应     

Tunneling Effect in Polythiophene

Polythiophene has been chemically synthesized using 2,5– dibromothiophene by debromination with magnesium, catalyzed by nickel chloride. The synthesized polymer was undoped using liquid ammonia and then doped again using 5% (wt/volume) aqueous FeCl₃ for 2.5, 5 and 10 hour duration. Characterization of undoped as well as doped samples using elemental analysis and FTIR has been carried out. Elemental analysis shows that concentration of Fe⁺ atoms increases as the duration of doping increases. The FTIR spectrum reveals the complex formation between FeCl₃ and polythiophene. All samples were pressed into pellets of about 1cm in diameter. The pellets were coated with gold (Au) on one side and with aluminum (Al) on other side using vacuum deposition technique. I–V measurements of undoped and FeCl₃ doped samples, after coating have been carried out using two probe method. I–V measurements, at room temperature, were carried out by applying d. c. voltage with +ve potential to the side of the pellet coated with Au and –ve potential to Al from 0 V to 1 V in step of 0.01 V and then from 1V to 15 V in step of 0.5 V. The measurements were again carried out after interchanging the polarity of the applied voltage. These characteristics are just similar to the characteristics of conventional tunnel diode in forward bias condition and like Schottky diode in reverse bias condition. Various parameters of tunnel diode such as figure of merit, voltage spread, noise figure etc are calculated using the measurements carried out. Noise figure value of undoped polythiophene is very close to ideal value. The performance of all FeCl₃ doped sample reduces, however value of the current ratio I_p/I_v (figure of merit) value for 5 hr. FeCl₃ doped polythiophene sample matches with that of silicon (Si) tunnel diode.     

固态Photo-CIDNP效应

光化学诱导动态核极化(photo-CIDNP)是一种在光照条件下由于产生非玻尔兹曼核自旋极化而使核磁共振(NMR)波谱信号强度发生明显变化的效应。这种效应在液体NMR中已为人所熟知,并通过经典的自由基对机理得到解释。固态photo-CIDNP效应发现的较晚,本文介绍了在光合反应中心及蓝光受体中发现的固态photo-CIDNP效应,详细阐述了固态photo-CIDNP效应产生的自由基对自旋动力学的机理,包括三旋混合(TSM)、衰变差异(DD)和弛豫差异(DR),重点介绍了类球红杆菌光合反应中心固态photo-CIDNP效应的磁场依赖性,这种场依赖性在同一分子中的不同核之间表现出明显的差异。本文综述了固态photo-CIDNP效应的现象、理论及其磁场依赖特性的最新进展。     

Frequency-Swept Integrated Solid Effect

The efficiency of continuous wave dynamic nuclear polarization (DNP) experiments decreases at the high magnetic fields used in contemporary high-resolution NMR applications. To recover the expected signal enhancements from DNP, we explored time domain experiments such as NOVEL which matches the electron Rabi frequency to the nuclear Larmor frequency to mediate polarization transfer. However, satisfying this matching condition at high frequencies is technically demanding. As an alternative we report here frequency-swept integrated solid effect (FS-ISE) experiments that allow low power sweeps of the exciting microwave frequencies to constructively integrate the negative and positive polarizations of the solid effect, thereby producing a polarization efficiency comparable to (±10 % difference) NOVEL. Finally, the microwave frequency modulation results in field profiles that exhibit new features that we coin the “stretched” solid effect.     

查耳酮类化合物的代基效应

查耳酮类化合物是一类合流型三岔共轭化合物。对于这类三岔共轭体系中的结构效应,前文中已在同系线性规律的基础上进行了比较系统的研究。但对于作为代基一岔的结构效应研究的不多,对于不同电性的取代基引入苯基后,所导致的同系直线斜率的变化是否与取代基的极性存在一定关系,尚待进行研究。本文合成了5个苯多烯基4＇-取代苯基酮系共20个化合物和一个相应的线型体系——苯多烯醛。研究了     

Electron-Proton Effect in Catalysis

The essence of the electron-proton effect is described with donor-acceptor complexes of quinones with hydroquinones as example. It is shown that this effect frequently occurs in organic chemistry and plays an important role in noncatalytic and catalytic reactions.     

超共轭与立体电子效应

回顾了超共轭概念的起源与发展,简述了超共轭效应在立体电子效应中的重要地位及其对于分子构象和反应活性的重要影响,并对乙烷的优势构象成因进行了讨论。     

结构因素和配位效应对室温本体聚合的影响

考察了丙烯酸乙酯(EA)、甲基丙烯酸甲酯(MMA)、苯乙烯(St)和丙烯腈(AN)四种不同结构特征的乙烯基单体和桐油(TO)、蓖麻油(CO)两种生物质油在室温(25℃)下以氧化还原引发体系引发的本体均聚合和共聚合反应,以及环烷酸钴的配位效应对聚合的影响。结果表明,室温下取代基的供电性或共轭性越强的单取代烯烃逾难均聚合;苯乙烯不能均聚,也不能与丙烯酸乙酯共聚合;由于空间位阻的原因,桐油和蓖麻油的均聚合以及与其它单体的共聚合在常温下均不能进行;环烷酸钴的配位效应能够提高单体和自由基的活性,促进聚合反应进行。     

Bis‐Gadolinium Complexes for Solid Effect and Cross Effect Dynamic Nuclear Polarization

High‐spin complexes act as polarizing agents (PAs) for dynamic nuclear polarization (DNP) in solid‐state NMR spectroscopy and feature promising aspects towards biomolecular DNP. We present a study on bis(Gd‐chelate)s which enable cross effect (CE) DNP owing to spatial confinement of two dipolar‐coupled electron spins. Their well‐defined Gd⋅⋅⋅Gd distances in the range of 1.2–3.4 nm allowed us to elucidate the Gd⋅⋅⋅Gd distance dependence of the DNP mechanism and NMR signal enhancement. We found that Gd⋅⋅⋅Gd distances above 2.1 nm result in solid effect DNP while distances between 1.2 and 2.1 nm enable CE for ¹H, ¹³C, and ¹⁵N nuclear spins. We compare 263 GHz electron paramagnetic resonance (EPR) spectra with the obtained DNP field profiles and discuss possible CE matching conditions within the high‐spin system and the influence of dipolar broadening of the EPR signal. Our findings foster the understanding of the CE mechanism and the design of high‐spin PAs for specific applications of DNP.     

复合稀土对Fe-Mn-Si-Ni-C合金形状记忆效应的影响

通过弯曲法测量、热循环训练、扫描电镜、X射线衍射等方法，研究了复合稀土对Fe-Mn-Si-Ni-C合金形状记忆效应的影响。研究结果表明，Fe-Mn-Si-Ni-C合金中加入复合稀土，能够明显细化合金的金相组织，显著提高合金的形状记忆效应，并使合金表现出微弱的双程记忆效应。试验结果还表明，第一种训练途径以及加入微量复合稀土是降低应力诱发ε马氏体稳定化行之有效的方法，X射线衍射结果表明，该训练方法有助于提高合金中ε→γ转变的ε逆转变率，对提高合金的记忆性能起积极的作用。     

Seebeck Effect in Colloidal Electrolytes

Russian Journal of Electrochemistry - A formalism is proposed that combines information on the Seebeck thermoelectric effect in highly conductive media and the Soret process associated with...     

氯化镧拮抗内毒素作用的初步研究

用定量鲎基质显色法测定LaCl3结合内毒素（LPS）的能力。通过ELISA，荧光宣RT－PCR方法观察LaCl3对LPS诱导的小鼠腹腔巨噬细胞（Mψ）肿瘤坏死因子－α（TNF－α）分泌及TNF－αmRNA表达的影响。通过小鼠死亡观察LaCl3和LPS毒性的影响。结果显示LaCl3具有结合LPS，抑制TNF－α分泌及TNF－αmRNA表达，降低LPS毒性的作用。     

有机化学中的异头效应

与共轭效应、诱导效应和螺共轭效应一样,异头效应(anomeric effect)是有机化学中特殊的立体电子效应。在新型有机染料、医药、农药等高科技领域具有重要的理论意义。对理解有机反应的机理、预测反应产物的结构以及生理活性与结构的关系具有重要的意义,并能达到相当高的准确性。     

Photoviscosity Effect of Polymer Solutions

Poly(methyl methacrylate) and poly(methacrylic acid) having spirobenzopyran in the side groups and polyamide having azobenzene in the main chain were synthesized in attempting to construct photoresponsive polymer systems, the conformation of which can be photoregulated. The solution viscosity in benzene of poly(methyl methacrylate) containing spirobenzopyran groups (9 mole% in base unit) during irradiation was found to be 12% lower than the viscosity in the dark. The viscosity is restored to the initial value in less than 3 min in the dark after cutting off the light. A study of the solvent effect and a spectroscopic study have verified that the photoviscosity effect is due to the self-solvation of the ester side groups to the photo-produced merocyanines. Photoregulation of the polymer conformation was also achieved in methanol for poly(methacrylic acid) having spirobenzopyran and in dimethylacetamide for a polyamide having azobenzene in the main chain.