物理有机化学前沿领域两个重要方面--有机分子簇集和自由基化学的研究

有机分子簇集和自卷是研究疏水亲脂作用（HLI）最基本和最简单的模型，它直接影响受体分子的反应性和生物功能，用物理有机化学的概念和方法研究簇集和自卷是了解HLI最好的途径之一。自由基化学研究中，取代三氟苯乙烯是迄今为止唯一可真正拆分取代基极性效应和自旋离域效应的体系。σJJ是最可靠和种类最多的反映取代基自旋离域能力的参数，首次提出一般情况下，可用双参数方程系数|ρ^＋/ρJJ|比值作为取代基极性效应和自旋离域效应相对权重的判别尺度，将自由基反应及波谱参数的相关分析分为四种类型，成功解决了长期困扰自由基化学界如何评估这两种效应的重大问题。     

一种计算取代基常数的简易方法

在共轭体系中,取代基的电性效应通常指诱导效应和共轭效应的总和,取代基常数包括诱导效应指数(I)和共轭效应指数(C)两部分。本世纪三十年代,出现了著名的Hammett方程和Hammett常数(σ)。蒋明谦等利用元素电负性和原子的共价半径两种基本常数,又提出了一种计算取代基的诱导效应指数(I)和共轭效应指数(C)的经验公式,并根据计算出来的诱导效应指数和共轭效应指数,定义了一种取代基常数——代基当量(S)。代基当量可用来解释某些有机分子的物理性质、化学     

拓扑立体效应指数及其应用

立体效应是有机化学中一种非常重要的取代基效应,对此曾提出不少计算方法[1～3],但目前尚不完善.本文考虑一给定取代基对反应中心屏蔽的空间概率,定义拓扑立体效应指数(Topological steric effect index,简称TSEI).此参数基于两个基本假设:一是分子或基团中的原子近似于球形;二是原子间的化学键可以自由旋转.TSEI的计算如下:     

在离子液体体系中苯环上氯取代基电子效应差异性研究

在1-丁基-3-甲基咪唑四氟硼酸盐([Bmim]BF4)离子液体中,研究不同取代基的苯氧负离子与溴代异丙烷亲核取代反应及不同取代基的苯甲醛与脲、乙酰乙酸乙酯亲核加成反应活性,通过测定反应转化率获得离子液体体系中不同取代基的电子效应.研究发现氯取代基表现出推电子性质,进而提出在离子液体体系中带苯环结构的反应物可与含杂芳环离子液体形成多层大π配合物结构,大π配合物影响了极性基团的正常溶剂化效应形成,产生独特的离子层溶剂效应.     

烯烃加成反应活性与烷基极化效应的关系

烯烃的自由基加成和亲电加成速率受不同的因素控制.对于仅仅含烷基取代的简单烯烃:(1)与OH自由基加成速率-log kOH可由π键上烷基极化效应指数的几何平均值GMPEIπ关联:-log kOH=a bGMPEIπ c(GMPEIπ)2; (2)与亲电试剂加成速率log k可由π键两端碳原子所连基团极化效应指数PEI(L)和PEI(S)关联:log k=a bPEI(L) cPEI(S),其中的PEI(L)和PEI(S)分别表示极化效应较大和较小的一端.     

基团共轭效应研究Ⅱ：^13C核磁共振的化学位移与取代基的共轭效应强度

引言在定量和定性研究有机化合物的结构与性质的关系中,最广泛使用的是Hammett等所提出的σ_m、σ_p等取代基常数以及基团的诱导(场)效应和共轭效应常数。在建立基团的共轭效应常数方面,人们做了大量的工作,但多数工作是基于对基团的Hammett常数σ的人为分解上,建立的模型和分解方式(系数因子)不同,则得到不同的结果。另一方面纯理论计算工作大多引入较多参数,使计算复杂和使用不便。作者曾在建立表征诱导效应大小的     

密度泛函活性理论中的信息论方法

密度泛函活性理论(DFRT)运用简单的密度泛函探讨和定量化分子的反应活性,是近来发展起来的一个关于分子活性理论的新方法。在新近的文献中,这样的简单密度泛函的例子包括香农熵,费舍尔信息以及其它来自信息论中的密度泛函。本文综述了DFRT信息论方法的原理,包括物理信息极小原理、最小信息增益原理和信息守恒原理。总结了DFRT信息论方法在电子密度、形态密度和分子中的原子三种表述下的理论框架。此外,还介绍了运用信息论方法在定量描述空间位阻效应、亲电性、亲核性和区域选择性中的突出应用,以及对亲电芳香取代反应的邻对间位取代效应的起源和本质提供的一个全新诠释。最后简要地展望了该领域的几个可能的未来发展方向。     

烷基极化效应的研究

烷基极化效应的研究曹晨忠（湘潭师范学院化学系，湖南４１１１００）极化效应是取代基的４种基本效应（场效应、电负性效应、极化效应和共轭效应￣［１］）之一，物理有机化学工作者一直期望对其进行定量化。Ｔａｆｔ￣［１，２］等曾计算出某些取代基的极化势，成功地解...     

含邻手性碳原子双键亲电加成反应的立体选择性模型

本文主要介绍了预测邻位具有手性中心π体系亲电加成反应的立体选择性模型,尤其是α,β-不饱和羰基化合物亲核共轭加成形成的烯醇负离子及其类似物和硝基烯烃亲核加成形成的氮酸根类中间体的烷基化和动力学控制质子化反应的立体选择性模型。立体位阻效应控制的Zimmerman前过渡态模型主要适用于底物构象受限的环状或联烯型烯醇负离子的动力学质子化。对于构象转化相对灵活的直链底物,Houk基于量子化学计算研究提出了亲电试剂的进攻角度或接触角在经过环状过渡态时是锐角还是钝角决定了亲电加成反应的立体选择性控制(Houk模型)。而Fleming模型首次将烯丙基A-1,3张力引入各类烯醇负离子烷基化和质子化的过渡态。Mohrig模型在考虑A-1,3张力的基础上,将吸电子取代基与即将形成的σ键反式共平面,主要阐述了立体电子效应对酯的烯醇负离子动力学控制质子化立体选择性的影响,后来又提出了金属离子参与的立体电子效应控制的六元环状半椅式模型。本文希望对理解亲电加成反应的立体化学控制提供一些有用的信息。     

溶剂效应和取代基效应对2-(2-氨基苯基)苯并噻唑光谱性质及激发态分子内质子转移的影响

合成了多种2-(2-氨基苯基)苯并噻唑(APBT)氨基氢原子被供电子及吸电子基团取代的衍生物, 并用紫外光谱﹑荧光光谱等方法和密度泛函理论(DFT)计算研究了溶剂效应和取代基效应对衍生物的光谱性质及激发态分子内质子转移(ESIPT)的影响规律. 结果表明, 相比于非极性溶剂环己烷, 随溶剂极性的增加及APBT-溶剂分子间氢键的形成, APBT的紫外-可见最大吸收峰和荧光最大发射峰均发生了一定程度的红移, 并对APBT的ESIPT产生了影响. 在APBT分子的氨基氮原子上引入不同的吸电子或斥电子取代基, 对氮原子的电荷性质有较大的影响. 在环己烷溶剂中, 甲基取代后的APBT仅有单重荧光发射峰, 体系未发生ESIPT过程; 而COCH₂Cl等吸电子基团能促进APBT的ESIPT, 其荧光发射光谱出现了明显的双重峰, 表明体系发生了激发态分子内质子转移反应. 量子化学的理论计算较好地验证了光谱实验结果.     

Recent progress in quantifying substituent effects

This paper summarizes significant progress in quantifying organic substituent effects in the last 20 years. The main content is as follows: (1) The principle of electronegativity equalization has gained wide acceptance, and has been used to calculate the intramolecular charge distribution and inductive effect of groups. A valence electrons equalization method was proposed to compute the molecular electronegativity on the basis of geometric mean method, harmonic mean method, and weighted mean method. This new calculation method further extended the application of the principle of electronegativity equalization. (2) A scale method was established for experimentally determining the electrophilic and nucleophilic ability of reagents, in which benzhydryliumions and quinone methides were taken as the reference compounds, and the research field was extended to the gas phase conditions, organometallic reaction and radicals system. Moreover, the nucleophilicity parameters N and electrophilicity parameters E for a series of reagents were obtained. The definition and quantitative expression of electrophilicity index and nucleophilicity index were proposed theoretically, and the correlation between the parameters from experimental determination and the indexes from theoretical calculation was also investigated. (3) The polarizability effect parameter was initially calculated by empirical method and further developed by quantum chemistry method. Recently, the polarizability effect index of alkyl (PEI) and groups (PEI X ) were proposed by statistical method, and got wide applications in explaining and estimating gas-phase acidity and basicity, ionization energy, enthalpy of formation, bond energy, reaction rate, water solubility and chromatographic retention for organic compounds. (4) The excited-state substituent constant ex CC obtained directly from the UV absorption energy data of substituted benzenes, is different from the polar constants in molecular ground state and the radical spin-delocalization effects constants in molecular radical state. The proposed constant ex CC correlated well with the UV absorption energy of many kinds of organic compounds, such as 1,4-disubstituted benzenes, substituted stilbenes, and disubstituted N-benzylidenebenzenamine. (5) The establishment of the steric shielding effect distinguished the three traditional steric effects. The stereoselectivity index C i was proposed to quantify the stereoselectivity of the addition reaction of carbonyl with nucleophilic reagent. The shielding parameter S R was defined to quantitatively express the specific surface of the reaction center screened by a group. Further, the Topological Steric Effect Index (TSEI) of a group was proposed on the basis of the relative specific volume of reaction center screened by the atoms of substituents. These parameters can be applied in estimating the intramolecular dihedral angles, stereoselectivity of reaction, enthalpies of formation of alkenes and alkylbenzene, acidity of substitutedimidazolium ionic liquid, and the reaction rate of alkane and hydroxyl radical. In addition, some suggestions and prospects for further studies on quantifying the organic substituent effects were presented in this paper.     

烷烃与羟基自由基反应速率常数的估算

Activation energy of hydroxyl radical OH reacting with alkanes was estimated from the quantitative relation between the bond dissociation energy (BDE) of Ri-H and the polarizability effect index (PEI) of alkyl radical Ri. Preexponential factor A in Arrhenius expression quantitatively was related to the topological steric effect index (TSEI) of alkyl radical Ri. The research results show that three parameters, PEI, TSEI and temperature T, can be used to quantify the activity of hydroxyl radical reacting with primary, secondary and tertiary carbon hydrogen bonds in alkane. The expression can accuratly evaluate the activity of C-H bonds. Moreover, the PEI and TSEI of alkyl radical Ri can be correlated quantitatively with the reaction absolute and relative rates of alkanes and cyclanes with hydroxyl radicals at various temperatures. The predicted rate constants are in good agreement with the experimental ones.     

若干有机合成反应的构象效应

通过分析竞争反应的过渡态在构象上能量的高低,探讨构象效应(立体电子效应和位阻效应)对一些有机反应的立体性的影响;而立体电子效应和位阻效应与反应机制,反应物的结构-构象和反应条件等都有关系,最终能影响反应产物的立体结构。阐明其中的缘由可有助于正确预测产物的结构及选择可行的合成线路。     

共轭烯烃的共轭极化势

Based on the conjugated polarization theory,it is expressed as the conjugated polarizability potential （CPP）that the discrepancy between the average electrostatic energy of dipolar state and the electrostatic energy of non-polar state in the conjugated polarizability procedure for the conjugated alkenes. The correlation between CPP and the energy of ultraviolet absorption maximum,and the correlation between the energy of frontier molecular orbital obtained by ab initio calculation of quantum chemistry and the energy of ultraviolet absorption maximum have been carried out for the conjugated alkenes. Both correlation equations show a similar estimated precision. Further, the contribution of alkyl polarizability effect to the stability of dipolar state for the alkyl substituted alkenes with the effective polarizability effect index（PEI（ef））was quantified. Relating the above two parameters CPP and PEI（ef）to the energy of ultraviolet absorption maximum of the substituted alkenes in a two-parameter expression with a good prediction ability was obtained:v=1.1746+5.0187CPP-0.43204PEI （ef）,R=0.9995,s=0.0403,F=10853.28,n=23. The investigated results also indicate that it is less effective to reduce the energy of ultraviolet absorption maximum by means of increasing the alkyl substituent groups than lengthening the conjugated backbone chain in the conjugated alkenes.     

Chain-growth polycondensation via the substituent effect: Investigation of the monomer structure on synthesis of poly(N-octyl-benzamide)

A systematic study of the behavior of different leaving groups on a variety of ester-based monomers was performed for the chain-growth polycondensation synthesis of poly(N-octyl benzamide). Linear and branched alkane esters were compared with their phenyl analogs using both computational and experimental methods. Kinetic experiments along with qualitative solubility observations were used, with the aid of nuclear magnetic resonance spectroscopy and gel-permeation chromatography, to determine progress of the reaction, molecular weights, and molecular weight distributions. It was found that the reactivity of the monomer's ester group depends more on the stability of the leaving alkoxide than the electrophilicity of the carbonyl carbon, which contradicts previous literature. The order of reactivity increases for the alkyl esters with decreasing steric hindrance and decreasing pKa of the substituent. For the phenyl ester derivatives, the more electron withdrawing character of a para substituent increases the reactivity of the ester group, due to the higher resonance stabilization of the leaving phenoxide anion, not due to an increase in the electrophilicity of the carbonyl carbon.     

1，4-二取代苯紫外吸收光谱中的取代基效应

构建激发态取代基参数与1,4-二取代苯的紫外吸收波数之间的模型,成功地关联80个1,4-二取代苯的紫外吸收波数,其方程的相关系数为0．9805,标准偏差仅为672．27cm^-1．结果表明激发态取代基参数适用于1,4-二取代苯紫外吸收能量的研究．同时提供了研究芳香化合物的紫外吸收光谱的新方法,并有利于深入理解多取代共轭化合物的激发态物理化学性质中的取代基效应．     

Substituent Effect on the C–NO2 and N–NO2 Bond Dissociation Energies of Nitroaromatic Molecules

Six density function theory methods (B3LYP, B3P86, MPWB1K1, MPWPW91, PBEPBE, TPSS1KCIS3) were used to calculate bond dissociation enthalpies of nitro compounds, where the B3P86 method was found to give the most accurate predictions. Using the B3P86 method meta‐ and para‐substituted nitroaromatics were systematically studied for the first time. The remote substituent effects, Hammett relationships, and the origin of the substituent effects were discussed on the basis of the calculated results. Both meta‐ and para‐substituted nitromethyl‐benzenes showed significant substituent effects and a fair correlation against substituent constants σ_p⁺ The ground state effects were found to play the major role in determining the overall substituent effects. Meanwhile, nitroamino‐ benzenes showed irregular substituent effects and a poorer Hammett correlation, where both ground and radical state effects contributed to the overall substituent effects.     

The nucleophilicity N index in organic chemistry

The nucleophilicity N index (J. Org. Chem. 2008, 73, 4615), the inverse of the electrophilicity, 1/ω, and the recently proposed inverse of the electrodonating power, 1/ω?, (J. Org. Chem. 2010, 75, 4957) have been checked toward (i) a series of single 5-substituted indoles for which rate constants are available, (ii) a series of para-substituted phenols, and for (iii) a series of 2,5-disubstituted bicyclic[2.2.1]hepta-2,5-dienes which display concurrently electrophilic and nucleophilic behaviors. While all considered indices account well for the nucleophilic behavior of organic molecules having a single substitution, the nucleophilicity N index works better for more complex molecules. Unlike, the inverse of the electrophilicity, 1/ω, (R(2) = 0.71), and the inverse of the electrodonating power, 1/ω? (R(2) = 0.83), a very good correlation of the nucleophilicity N index of twelve 2-substituted-6-methoxy-bicyclic[2.2.1]hepta-2,5-dienes versus the activation energy associated with the nucleophilic attack on 1,1-dicyanoethylene is found (R(2) = 0.99). This comparative study allows to assert that the nucleophilicity N index is a measure of the nucleophilicity of complex organic molecules displaying concurrently electrophilic and nucleophilic behaviors.     

取代基和溶剂对4,4＇-二取代二苯乙烯紫外吸收能量的影响

合成25个4,4＇-二取代二苯乙烯化合物,测定了这些化合物在环己烷、乙醚、三氯甲烷、乙腈和醇等10多种溶剂中紫外吸收光谱的最大波长,共得到242个实验数据.讨论了取代基效应和溶剂效应对其紫外吸收光谱最大波长能量的影响.研究结果表明：同种溶剂中4,4′-二取代二苯乙烯化合物紫外吸收最大波长的能量主要受其分子内部结构（取代基效应）的影响,即由取代基的激发态参数σCexC和基态的极性参数σp共同决定;不同溶剂中其紫外吸收最大波长的能量由取代基效应和溶剂效应共同决定.提出了定量估算4,4′-二取代二苯乙烯化合物紫外吸收能量方程.并且发现,以溶剂在水/正辛醇中分配系数logP比用溶剂显色参数ET（30）度量溶剂效应更加有效,所得的定量方程相关性更好,物理意义更为明确.用所得方程对文献报道的有关化合物的紫外吸收光谱进行了预测,结果与实验测定值相吻合.