理论化学在中国的发展

本文回顾1949年以来,我国理论化学的发展历史.全文始于“荒漠渐成绿洲”的总体概括,进入主体全面的论述.按1978年划分为前、后两期.前期为学科的成长成熟期,以创业人及少数从业者的科教活动为中心,后期为学科的繁荣期,以本学科现阶段中青年精英创造佳绩、进入学科主流领域为中心.按时间进程将前后期最有代表性的10个方面研究成...     

价电子对互斥理论与电价理论相结合判定分子的共轭类型

以价电子互斥理论与杂化轨道理论为基础,首先确定中心原子或离子的杂化类型以及总电子对的结构,并确定处于同一平面的原子;然后摒除σ键,仅分析π键,并根据价键理论,确定参加共轭的原子对共轭π键所贡献的电子数,最终达到对分子共轭类型的判别。     

_f-A_aD_d氢键体系的统计特征

基于氢键的形成和缩聚反应机理在统计意义下的相似性 ,利用高分子反应统计理论和反应动力学理论对氢键溶液的一个模型体系进行了相关讨论 .给出了体系的溶胶分数和发生溶胶 -凝胶相变的条件 ,指出质子受体基团间的竞争作用对溶胶凝胶相变点的影响 ,进而讨论了体系的数量分布函数和相关问题 .     

键能的分子轨道理论研究 1: 理论公式

从LCAO-MO出发, 给出了一个计算键能的近似方法, 即EAB(i)-∑∑CaiSabCbiεi为第i个占据分子轨道(MO)中的一对电子对A-B键键能的贡献。对所有分子轨道求和即为该键的键能: EAB=∑EAB(i)。按该方法, 不仅可以计算各种不同分子中每两个相键连原子间的键能, 还可以从MO及AO角度分析每一具体键, 如σ, π, δ键的键能以及各AO对键能的贡献。该方法虽有别于求键焓和平衡离解能De, 但计算结果和De的实验值甚相符合。通过对键能的分析研究, 能较好地揭示原子间的相互作用关系及化学键的强弱, 从而可进一步探讨化学反应活性, 反应速率等化学性质。     

_f-A_aD_d氢键体系的统计特征

基于氢键的形成和缩聚反应机理在统计意义下的相似性,利用高分子反应统计理论和反应动力学理论对氢键溶液的一个模型体系进行了相关讨论.给出了体系的溶胶分数和发生溶胶-凝胶相变的条件,指出质子受体基团间的竞争作用对溶胶凝胶相变点的影响,进而讨论了体系的数量分布函数和相关问题.     

导电胶粘剂的导电机理研究进展

综述了导电胶的导电机理.导电胶作为无铅焊焊料的替代品,相关研究已受到普遍的重视,但对导电胶导电机理研究的不足在一定程度上制约了其应用与发展.导电胶的导电机理相当复杂,通常可以分为导电通路如何形成与材料形成导电通路后如何导电这两个方面的内容来研究.对此,人们提出了许多阐述导电胶导电机理的理论和模型.本文详细介绍了渗流理论、界面热力学理论、有效介质理论、量子力学隧道效应理论等几种具有代表性的导电理论,对其适应范围、优缺点等进行了评述.     

BrSSCl和SSBrCl相对稳定性的理论研究

采用量子化学中的密度泛函理论，在B3LYP／6-311 G(3df)水平上全优化得到了S2BrCl分子线型和分叉型2种异构体的平衡结构，同时对可能发生的分子内原子迁移过程的过渡态进行了考察。计算结果表明，从能量角度看，线型的BrSSCl为稳定构型。采用统计热力学及过渡态理论，研究了Z种平衡结构之间相互转化的热力学和动力学性质。根据计算结果，无论是Cl迁移还是Br迁移，分子内的原子迁移都需要较高的活化能，并且迁移速度较慢。     

纯流体在临界区内外的表面张力研究

An equation of state(EOS)applicable for both the uniform and non-uniform fluids was established by using thedensity-gradient expansion,in which the influence parameter к[p(r),T] was obtained by the use of direct correlationfunction.The density functional theory(DFT)provides a framework under which both the phase equilibria and in-terfacial properties can be investigated within a single set of molecular parameters.The phase equilibria inside thecritical region can be improved by the renormalization group theory(RGT).However,the correction of interracialproperties by DFT and RGT is computationally difficult.In the present work,the density gradient theory(DGT)inwhich к[p(r),T] is treated as a constant is used to combine with the RGT for interfacial properties inside the criticalregion.     

键能的分子轨道理论研究 1: 理论公式

从LCAO-MO出发, 给出了一个计算键能的近似方法, 即EAB(i)-∑∑CaiSabCbiεi为第i个占据分子轨道(MO)中的一对电子对A-B键键能的贡献。对所有分子轨道求和即为该键的键能: EAB=∑EAB(i)。按该方法, 不仅可以计算各种不同分子中每两个相键连原子间的键能, 还可以从MO及AO角度分析每一具体键, 如σ, π, δ键的键能以及各AO对键能的贡献。该方法虽有别于求键焓和平衡离解能De, 但计算结果和De的实验值甚相符合。通过对键能的分析研究, 能较好地揭示原子间的相互作用关系及化学键的强弱, 从而可进一步探讨化学反应活性, 反应速率等化学性质。     

A partial proton transfer in hydrogen bond O-H···O in crystals of anhydrous potassium and rubidium complex chloranilates

Hydrogen bonding and proton transfer in the solid state are studied on the crystals of isostructural anhydrous potassium and rubidium complex chloranilates by variable-temperature single crystal X-ray diffraction, solid state (1)H NMR and IR spectroscopies, and periodic DFT calculations of equilibrium geometries, proton potentials, and NMR chemical shifts. Their crystal structures reveal neutral molecules of chloranilic acid and its dianions connected into a chain by O-H···O hydrogen bond. A strong hydrogen bond with a large-amplitude movement of the proton with NMR shift of 13-17 ppm and a broad continuum in IR spectra between 1000 and 500 cm(-1) were observed. Periodic DFT calculations suggest that proton transfer is energetically more favorable if it occurs within a single pair of chloranilate dianion and chloranilic acid molecule but not continuously along the chains of long periodicity. The calculated chemical shifts confirm the assumption that the weak resonance signals observed at lower magnetic fields pertain to the case when the proton migrates to the acceptor side of the hydrogen bond. The detected situation can be described by a partial proton transfer.     

Spectroscopic and computational studies of aqueous ethylene glycol solution surfaces

The combination of Monte Carlo, ab initio, and DFT computational studies of ethylene glycol (EG) and EG-water hydrogen-bonding complexes indicate that experimental vibrational spectra of EG and EG-water solution surfaces have contributions from numerous conformations of both EG and EG-water. The computed spectra, derived from harmonic vibrational frequency calculations and a theoretical Boltzmann distribution, show similarity to the experimental surface vibrational spectra of EG taken by broad-bandwidth sum frequency generation (SFG) spectroscopy. This similarity suggests that, at the EG and aqueous EG surfaces, there are numerous coexisting conformations of stable EG and EG-water complexes. A blue shift of the CH2 symmetric stretch peak in the SFG spectra was observed with an increase in the water concentration. This change indicates that EG behaves as a hydrogen-bond acceptor when solvated by additional water molecules. This also suggests that, in aqueous solutions of EG, EG-EG aggregates are unlikely to exist. The experimental blue shift is consistent with the results from the computational studies.     

N’-苄基酰腙分子的氮-氮键旋转位阻及分子构象

采用动态核磁共振波谱(DNMR)和密度泛函理论(DFT)对N'-苄基酰腙化合物进行构象研究. 实验和理论计算表明, 1H NMR图谱中三组不同质子的双峰裂分是由N—N键旋转位阻造成的, 而这三个双峰裂分的化学位移差异随温度升高而减小. 通过模拟化学位移差异与温度的关系, 得到了交换速率常数, 采用Eyring方程计算出N—N键旋转位阻. 提出顺式和反式共存的模型来分析酰胺质子信号分裂的原因, 并利用DFT计算得出优化的异构体构象及其最低能量. 端甲基质子和次甲基质子信号裂分也来源于N—N键旋转受阻. N'-苄基酰腙通过缩合反应转变成1,3,4-二唑化合物, 消除了甲基空间取向的差异, 其信号变为单峰.     

Weakly and strongly associated nonfreezable water bound in bones

Water bound in bone of rat tail vertebrae was investigated by ¹H NMR spectroscopy at 210–300 K and by the thermally stimulated depolarization current (TSDC) method at 190–265 K. The ¹H NMR spectra of water clusters were calculated by the GIAO method with the B3LYP/6-31G(d,p) basis set, and the solvent effects were analyzed by the HF/SM5.45/6-31G(d) method. The ¹H NMR spectra of water in bone tissue include two signals that can be assigned to typical water (chemical shift of proton resonance δ_H = 4–5 ppm) and unusual water (δ_H = 1.2–1.7 ppm). According to the quantum chemical calculations, the latter can be attributed to water molecules without the hydrogen bonds through the hydrogen atoms, e.g., interacting with hydrophobic environment. An increase in the amount of water in bone leads to an increase in the amount of typical water, which is characterized by higher associativity (i.e., a larger average number of hydrogen bonds per molecule) and fills larger pores, cavities and pockets in bone tissue.     

Quantum chemical computations of 1,3-phenylenediacetic acid

Molecular geometry, vibrational wavenumbers and gauge including atomic orbital (GIAO) 13C NMR and 1H NMR chemical shift values of 1,3-phenylenediacetic acid (C10H10O4), in the ground state have been calculated by using ab initio Hartree-Fock (HF) and density functional theory (DFT/B3LYP) methods with 6-311++G(d,p) basis set for the first time. Comparison of the observed fundamental vibrational modes of 1,3-phenylenediacetic acid and calculated results by density functional B3LYP and Hartree-Fock methods indicate that B3LYP is superior to the scaled Hartree-Fock approach for quantum chemical studies. Geometric parameters (bond lengths and bond angles) and vibrational wavenumbers obtained by the HF and DFT/B3LYP methods are in good agreement with the experimental data. Furthermore, this is the first time the results of the calculated JCH and JCC coupling constants of the C10H10O4 molecule are presented in this study.     

Visualization and quantification of the anisotropic effect of C=C double bonds on 1H NMR spectra of highly congested hydrocarbons-indirect estimates of steric strain

The anisotropic effect of the olefinic C=C double bond has been calculated by employing the NICS ( nucleus independent chemical shift) concept and visualized as an anisotropic cone by a through space NMR shielding grid. Sign and size of this spatial effect on (1)H chemical shifts of protons in norbornene, exo- and endo-2-methylnorbornenes, and in three highly congested tetracyclic norbornene analogs have been compared with the experimental (1)H NMR spectra as far as published. (1)H NMR spectra have also been calculated at the HF/6-31G* level of theory to get a full, comparable set of proton chemical shifts. Differences between delta( (1)H)/ppm and the calculated anisotropic effect of the CC double bond are discussed in terms of the steric compression that occurs in the compounds studied.     

A New Metric for Evaluating DFT Calculated Proton and Carbon Chemical Shifts of Natural Products and Organic Compounds

The calculation of DFT (density functional theory) chemical shifts have become an important technique for the verification of a proposed structure. An easily calculated metric developed for proton and carbon chemical shifts of natural products and organic compounds, the calculated chemical shift index (CCSI), has been developed, which uses the deviation of each pair of calculated and experimental chemical shifts. The mean absolute deviation (MAD), which is commonly used as the goodness of fit metric for DFT calculated chemical shifts, can conceal large deviations in the calculated data. A classification strategy is also proposed for the CCSI to highlight when further assessment of the NMR data is required.     

Thermal properties and mixing state of ethylene glycol-water binary solutions by calorimetry, large-angle X-ray scattering, and small-angle neutron scattering

Thermal properties and mixing states of ethylene glycol (EG)-water binary solutions in the entire mole fraction range of EG, 0 < or = x(EG) < or = 1, have been clarified by using differential scanning calorimetry (DSC), large-angle X-ray scattering (LAXS), and small-angle neutron scattering (SANS) techniques. The DSC curves obtained have shown that the EG-water solutions over the range of EG mole fraction 0.3 < or = x(EG) < or = 0.5 are kept in the supercooling state until approximately 100 K, and those in the range of 0.6 < or = x(EG) < or = 0.8 are vitrified, and those in the ranges of 0 < x(EG) < or = 0.2 and 0.9 < or = x(EG) < 1 are crystallized. The radial distribution function (RDF) for pure EG obtained from the LAXS measurements has suggested that a gauche conformation of an EG molecule is favorable in the liquid. The RDFs for the EG-water solutions have shown that the structure of the binary solutions moderately changes from the inherent structure of EG to the tetrahedral-like structure of water when the water content increases. The SANS intensities for deuterated ethylene glycol (HOCD2CD2OH) (EGd4)-water solutions at x(EG) = 0.4 and 0.6 have not been significantly observed in the temperature range from 298 to 173 K, showing that EG and water molecules are homogeneously mixed. On the other hand, the SANS intensities at x(EG) = 0.2 and 0.9 have been strengthened when the temperature decreases due to crystallization of the solutions. On the basis of all the present results, a relation between thermal properties of EG-water binary solutions and their mixing states clarified by the LAXS and SANS measurements has been discussed at the molecular level.     

基于LFHB 理论模型关联和预测醇+惰性溶剂的1H NMR 化学位移

运用含氢键缔合的格子流体状态方程(LFHB), 仅用一个参数关联了一元醇-惰性溶剂共17个体系29套1H NMR化学位移数据. 并且用关联参数成功预测了不同温度下丁醇+环己烷的化学位移. 所得结果与化学缔合理论的结果进行了比较. 对于某些体系在稀浓度范围LFHB的计算氢键缔合度要低于化学缔合理论的结果. 并且分析了LFHB理论中的物理参数和化学参数对于缔合度计算的不同影响.     

Ab initio and NMR studies on the effect of hydration on the chemical shift of hydroxy protons in carbohydrates using disaccharides and water/methanol/ethers as model systems

Density functional theory (DFT) and Hartree-Fock (HF) quantum mechanical calculations have been performed on the disaccharides, [small beta]-l-Fucp-(1[rightward arrow]4)-[small alpha]-d-Galp-OMe, [small beta]-l-Fucp-(1[rightward arrow]4)-[small alpha]-d-Glcp-OMe, and [small beta]-l-Fucp-(1[rightward arrow]3)-[small alpha]-d-Glcp-OMe. The [capital Delta][small delta]-values (difference between the chemical shift in the disaccharide and the corresponding monosaccharide methyl glycoside) for the exchangeable hydroxy protons have been calculated and compared to experimental values previously measured by NMR spectroscopy for samples in aqueous solutions. The calculations performed on molecules in vacuum showed that hydroxy protons hydrogen bonded to the neighboring ring oxygens have large positive [capital Delta][small delta]-values, indicating that they are deshielded relative to those in the corresponding methyl glycoside. The NMR experiments showed instead that these hydroxy protons close to the neighboring ring oxygens were shielded. This discrepancy between calculated and experimental data was attributed to solvent effects, and this hypothesis has been confirmed in this work by monitoring the chemical shift of the hydroxy proton of methanol in water, ethers and water/ether solutions. Shielding of the hydroxy proton of methanol is observed for increased ether concentrations, whereas deshielding is observed for increased concentration of water. The shielding observed for hydroxy protons in disaccharides is a consequence of reduced hydration due to intermolecular hydrogen bonding or steric effects. In strongly hydrated systems such as carbohydrates, the hydration state of a hydroxy proton is the key factor determining the value of the chemical shift of its NMR signal, and the [capital Delta][small delta] will be a direct measure of the change in hydration state.