On QSAR Study of Stereoselectivity for Wittig Reaction

1INTRODUCTION Witting reaction is an important and well-known organic reaction.In this reaction system,phospho-nium ylides react with aldehydes or ketones to gene-rate olefins and phosphonium oxides.Obviously,the position of double bond in olefins is exactly the po-sition of carbonyl group in the reactants,so there are no other position isomers in products.Due to this advantage,Witting reaction has been widely used in organic synthesis[1].Witting reaction could introduce double bond to c…     

利用浮动电荷力场对N-甲基乙酰胺水溶液的分子动力学模拟

利用原子键电负性均衡结合分子力场方法(ABEEM/MM)对N-甲基乙酰胺(NMA)分子的水溶液体系进行了分子动力学模拟. 与经典的力场模型相比, 该方法中的静电势包含了分子内和分子间的静电极化作用, 以及分子内电荷转移影响, 同时加入了化学键等非原子中心电荷位点, 合理体现了分子中的电荷分布. 相对其它极化力场模型, 该模型具有计算量较小的特点. 在该模型下对NMA纯溶液和其水溶液体系进行了分子动力学模拟, 得到的径向分布函数、汽化热和偶极矩等物理量与实验值和其它极化力场方法符合很好, 合理描述了溶质与溶剂之间的静电极化和分子内的电荷转移.     

Enthalpies of formation of monoderivatives of hydrocarbons: Interaction of polar groups with an alkyl group

Energies of hydrocarbon monoderivatives CH(3)X, C(2)H(5)X, n-C(4)H(9)X, and n-C(5)H(11)X with 16 different substituents X were calculated at the levels B3LYP/6-311+G(d,p) and B3LYP/AUG-cc-pVTZ//B3LYP/6-311+G(d,p). The results were used to test the validity of the additive rule that has served commonly for estimating the enthalpies of formation Delta(f)H(T). The exact additivity corresponds to zero reaction energy DeltaE of the isodesmic reaction, in which the substituent X is transferred from one alkyl group R to another. Additivity is approximately fulfilled for butyl and pentyl derivatives with the differences less than 0.3 kJ mol(-1) (except charged groups X). Methyl derivatives deviated from the additive rule up to 22 kJ mol(-1) for dipolar groups X and 45 kJ mol(-1) for charged group, in agreement with the available experiments and with the anticipation of all suggested empirical schemes. In addition, smaller deviations of ethyl derivatives (3 or 20 kJ mol(-1), respectively) were observed here for the first time. There is no correlation between the deviations of methyl and ethyl derivatives; they are also not related to steric effects, and only partly to polarization. Deviations of methyl derivatives are proportional to the electronegativity of the first atom of the substituent; even when the definition of electronegativity is somewhat questionable, one can say in any case that it is controlled by the first atom.     

Dissociation energies for the electronic ground states of BeCl,GaH and LiH

The dissociation energies of the diatomic molecules BeCl, GaH and LiH have been computed by fitting empirical potential functions to the true potential energy curves for the electronic ground states of the molecules. The Lippincott three-parameter potential function, the five-parameter Hulburt-Hirschfelder potential function and the Szöke and Baitz electronegativity potential function have been used. The estimated dissociation energiesD ₀ ⁰ are 4·50, 3·09 and 2·94 eV for BeCl, GaH and LiH respectively. These values compare well with the experimental values.     

原子-键电负性均衡方法参数的确定与探讨

原子-键电负性均衡方法(ABEEM)是以密度泛函理论(DFT)和电负性均衡原理为基础发展而来，它明确地考虑了化学键是不引入任何实验数据的带纯理论性和计算的方法．使用统一标准并具有代表性和全面性地选择了200多个模型分子，利用可得到较准确结构的MP2／6-31G*优化结构，心／STO-3G单点计算得到Mulliken重叠布居，再用最小二乘法拟合得到许多主族元素在分子体系中的诸原子(包括单、双和叁键等不同成键状态)和化学键的ABEEM参数．所得到的原子的价态电负性可与已提出的其他电负性标度相比拟，计算CO得到的电荷负端为C(与从头计算的结果相反)，结果与实验相符，且原子电荷的正负不完全由原子电负性决定．     

A CDOE/INDO LMO study of the nuclear spin-spin coupling constants between directly bonded C-H and C-C atoms

Müller-Pritchard (MP) type relations are used to study¹ J _CH and¹ J _CC coupling constants in a series of unsubstituted as well as in heterosubstituted hydrocarbons. In the case of the coupling constant between two atoms connected by a multiple bond, a generalised MP-type relation is derived.Aangesteld Navorser of the Belgian National Foundation for Scientific Research (N.F.W.O.)     

A new scale of atomic electronegativities

A new formula for the calculation of atomic electronegativities from the atomic size and nuclear effective charge is proposed. The formula has the same dimensionality as the one used for the thermochemical scale. The calculated ionic and van der Waals atomic electronegativities are used for the interpretation of the bond nature in binary and coordination compounds (in particular, the bond ionicity is calculated in molecules and crystals of the AB type).Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 32–37, January, 1993.     

单硫醚气相色谱保留指数拓扑化学研究

在分子拓扑化学理论的基础上,根据分子中原子的特性,用分子中原子的平衡电负性对分子图进行着色,在距离矩阵的基础上结合分子中各原子的支化度构建一组新的拓扑指数NPm(m=1,2,3),利用多元线性回归技术将单硫醚在4种极性固定相的气相色谱保留指数与NPm(m=1,2,3)建立相应的定量结构-保留相关关系模型(QSRR),并用这种模型对单硫醚的气相色谱保留指数进行预测,结果表明,预测结果和实验值吻合较好。     

饱和链状分子中C 1s电子电离能与基团拓扑电负性指数

由X-射线光电子谱测定的原子内层电子的电离能(也称结合能)能反映分子内部不同区域的原子特性,常用于估计分子内不同部位的化学活性、分子中的电子结构变化以及取代基效应[1]。还用于研究价电子性质[2-4]和化合物的气相酸碱性[5]。目前,对原子内层电子电离能的研究有实验测定和