键离子性与键长的计算

一、引言键长是分子结构的一个重要参数,对于化学键键长实验和计算,前人已做了许多工作。但键长和物质结构及性能的关系,各类无机物、有     

基于铁催化的C-H键活化构建C-C键的研究进展

过渡金属催化的C-H键活化及在此基础上的C-C键形成的反应因其高原子经济性和高效的合成效率而备受人们的关注.铁元素具有含量丰富、廉价、易得、环境友好等优点,在催化反应中得到了越来越广泛的应用.近几年来,人们关于Fe催化的C-H键活化构建C-C键反应的研究也取得了一定的进展.本文对铁催化的C-H键活化构建C-C键的最新研究进展作了综述,并且按照铁催化剂的不同价态进行了分类归纳,也对催化机理进行了阐述与总结.     

钨氧键价参数的研究

根据键价理论中的指数方程s_ij=exp[(R_o-r_ij)/B],利用晶体结构报告中不同氧化态n的329个W-O键长数据,选取不同的B值对键价参数R₀进行了拟合,建立了一系列R₀-n线性方程,并进而得到与W氧化态无关的键价参数R₀=0.1896 nm和B=0.028nm.与文献数据比较,本文拟合的键价参数取得了较好的键价和计算结果,讨论了几个应用的实例.     

分子间的非共价相互作用：σ-穴键和π-穴键

第四到第七主族元素以及惰性气体元素可以作为电子受体位点形成分子间吸引性的非共价键合作用。这些电子受体位点,即缺电子密度的位点,大多情况下具有正的分子表面静电势,可以将其分为2类。沿着σ共价键键轴延伸方向原子的外围中心具有正的分子表面静电势的区域称之为σ-穴。而垂直于分子σ-骨架平面具有正的分子表面静电势区域称之为π-穴。σ-穴和π-穴与富电性位点之间吸引性的相互作用分别称之为σ-穴键和π-穴键。σ-穴键倾向于180°,而π-穴键倾向于90°。按照元素周期表族的名称,σ-穴键又分为碳素键、氮素键、氧素键、卤键、惰素键等。可见流行的卤键只是σ-穴键的一个子集。π-穴键分类显得复杂些,可简单分为单原子和多原子π-穴键。     

镧系元素相关的键价参数研究

根据镧系元素络合物的晶体结构数据确定了单价键长R0的镧系收缩效应，并对已有的键价参数进行了系统的修订.建立了Ln-O键的R0对原子序数N在普适参数B=0.037 nm下的线性方程R0(nm)=0.2879－0.00132N.用不同参数进行键价和的计算并对结果进行了对比和讨论，最后展望了相关研究的前景.     

N—O键解离焓的密度泛函理论研究

在高精度计算方法G3和G3B3的基础上,比较了密度泛函理论(DFT)十几种方法对N—O键解离焓(BDE)相对于实验值的计算精度,发现用B3P86方法计算15种化合物N—O键的BDE,均方根误差最小,仅为6.36kJ·mol-1,计算值与实验值的线性相关系数为0.991.在此基础上,用该方法分别计算了非芳香化合物及芳香化合物的N—O键BDE.通过自然键轨道分析,发现部分N—O键的BDE与N—O键的键长、原子电荷密度及键级之间存在定量关系.此外,在B3P86方法的基础上预测了几种典型的杂环芳香化合物N—O键BDE值.     

键能的分子轨道理论研究Ⅱ.键能与Mulliken布居对键强度的判断的比较

用键能EAB和Mulliken布居对化学键强度的判别进行了分析比较.结果表明,键能判据比Mulliken布居判据所得结论更符合实际情况.作为衡量原子间化学键强度的尺度,不仅应考虑原子轨道间的布居因素,还应考虑分子轨道(或原子轨道)的能量因素.     

有机化学中几个键参数的讨论

有机化学中几个键参数的讨论周文富，赖文忠（福建三明师专化学系３６５００４）有机化学中共价键的一些重要属性，如键能、键长等。这些属性是判断有机分子结构和性质的重要参数；近年已引起不少学者的相继讨论￣［１－４］。有些教科书和文献在理论上提法的准确性不够。...     

铁的单核羰基络合物键能和成键特性的研究

通过电荷自洽叠代的ＥＨＭＯ量子化学计算,求得Ｆｅ（ＣＯ）５,ＰＸ５（Ｘ＝Ｆ,Ｃｌ）及Ｆｅ（ＣＯ）４Ｈ２分子的键能ＥＡＢ并分析它与键强度的关系,解释了Ｆｅ（ＣＯ）５分子中键长长的Ｆｅ－Ｃ键其键强度反而比键长短的Ｆｅ－Ｃ键强,Ｆｅ（ＣＯ）５和Ｆｅ（ＣＯ）４Ｈ２中Ｃ－Ｏ键键长相等,但键强度又不一样的“反常”现象     

季铵盐C—N键断裂构建C—X键的研究进展

胺类种类繁多, 原料易得. 胺类的C—N键键能较大, 一般需要通过活化再进行断裂. 近些年发展了多种氨基的活化方法, 其中把胺类转化为季铵盐的活化方法, 制备容易、存放稳定, 具有一定优势. 最近十年左右, 芳香胺和苄胺衍生的季铵盐通过C—N键断裂、构建各种C—X键的研究取得了巨大的研究进展. 本综述主要论述了最近几年需要和不需要过渡金属催化的季铵盐通过C—N键断裂构建C—X键的反应. 通过C—N键断裂, 季铵盐可以构建C—B键、C—C键、C—N键、C—O键、C—Si键、C—P键、C—S键、C—Se键等, 合成硼酸酯、芳烃、烷烃、醚类、胺类、硅烷、膦、硫醚、二硫化物、硒醚、二硒化物等化合物. 而且, 如果是采用手性苄胺衍生的季铵盐, 还可以得到多种高对映体纯的手性有机化合物; 季铵盐的手性在产物中保持良好, 并且, 对所有反应都发生S_N2型的构型翻转.     

19F NMR study of the polarization direction and polarity of tin-hydrogen and tin-transition metal bonds in tris(4-fluorophenyl)stannane and its organometallic derivatives

A series of (4-FC₆H₄)₃SnML _n compounds containing tin-transition metal bonds were synthesized. Based on¹⁹F NMR data for these compounds, (4-FC₆H₄)₃SnSn(C₆H₄F-4)₃, and (4-FC₆H₄)₃SnH, conclusions were drawn concerning the polarization direction and relative polarity of the tin-hydrogen and tin-metal bonds in the above compounds and in the hydrides L _n MH and R₃SnH. It was found that, in the general case, the group electronegativities of the L _n M groups do not vary similarly to the electronegativities of the central metal atoms.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1933–1937, November, 1994.     

Dynamic parameters of the hypervalent O3B...O bond

The results of investigations of the common and distinctive features of various chemical bonds, including intermolecular bonds, were considered. The geometries, atom charges, and force constants of the bonds in a dependent system of coordinates were calculated for five boroxide molecular species using the MINDO/3 method. The correlations found between the force constants and the bond energies in the O₃B...O bridge were compared with the analogous relations for the OH...O bridge. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2237–2241, December, 1999.     

Untersuchungen zur Carbeninsertion in Al–Al-, Ga–Ga- und In–In-Bindungen

Investigations on the Insertion of Carbenes into Al–Al, Ga–Ga, and In–In Bonds Tetrakis[bis(trimethylsilyl)methyl]dialane(4) 1 reacts with methylthiomethyl lithium LiCH₂SMe by the formation of lithium thiomethanolate LiSMe and the insertion of the remaining carbene CH₂ into its Al–Al single bond. A chelating Lewis acid is formed exhibiting a central R₂Al–CH₂–AlR₂ group with two coordinatively unsaturated Al atoms, which coordinate the thiomethanolate anion by Al–S bonds. The product (μ-methylene)(μ-thiomethanolato)bis{bis[bis(trimethylsilyl)methyl]aluminate} ( 4 ) was characterized by a crystal structure determination and has a strongly folded Al₂CS heterocycle in the molecular core. In contrast, the corresponding compounds with Ga–Ga or In–In bonds show on treatment with methylthiomethyl lithium a fragmentation, and the carbene intermediate could not be detected in both isolated products, which were identified as [R₂E(CH₂SMe)₂][Li(TMEDA)] (E = Ga: 5 ; E = In: 6 ) and LiCH(SiMe₃)₂ probably formed by a metal exchange reaction.     

多肽中氢键强度的理论研究

用B3LYP/6-31G^*法优化了多肽分子的几何构型,计算了各个构型的电荷分布和氢键酸度,进而对多肽分子中的氢键强度进行了研究.结果表明,多肽分子中氢键的强度同时取决于形成氢键的H…O原子间距R和N-H…O之间的键角β;多肽分子倾向于形成R值小、β值大的大环氢键.3₁₀螺旋结构的多肽分子中的氢键具有协同效应,分子越大,分子中氢键越多,氢键的协同效应越强.     

Dependence of (35)Cl NQR on hydrogen bonding and temperature in dichlorophenol-aniline charge transfer complexes

The hydrogen-bonded charge transfer complexes of aniline with pi-acceptors (or proton donors) such as 2,5-, 2,6-, 3,4- and 3,5-dichlorophenol were prepared. The (35)Cl nuclear quadrupole resonance (NQR) frequencies of these charge transfer complexes in the temperature range 77-300 K were measured to ascertain the existence or otherwise of a phase transition upon complex formation. Further, the NQR frequency and asymmetry parameter of the electric field gradient at the site of quadrupole nucleus were used to estimate the chemical bond parameters, namely ionic bond, double bond character of the carbon-chlorine(C--Cl) bond and the percentage charge transfer between the donor-acceptor components in charge transfer complexes. The effect of hydrogen bonding and temperature on the charge transfer process is analysed.     

共价键的离子化

本文用化学键理论分析和推导了共价键离子化的几种方式,包括金属和非金属单质中共价键的诱导离子化、化合物中共价键的降温和自诱导离子化以及含氢化合物和金属化合物的诱导离子化。从能量角度分析了离子化趋势的规律性,并且讨论了共价键的离子化的一些重要应用。     

氰化物与吡咯复合物氢键强度的理论研究

The R-C≡N…pyrrole (R=H, CH3, CH2F, CHF2, CF3, NH2, BH2, OH, F, CH2Cl, CHCl2, CCl3, Li, Na) complexes were considered as the simple sample for measure of hydrogen bonding strength. Density functional theory B3LYP/6-311 G^** level was applied to the optimization of geometries of complexes and monomers. Measure of hydrogen bonding strength based on geometrical and topological parameters, which were derived from the AIM theory, was analyzed. Additionally, natural bond orbital (NBO) analysis and frequency calculations were performed.From the computation results it was found that the electronic density at N-H bond critical points was also strictly correlated with the hydrogen bonding strength.     

取代基对N—H…O＝C氢键三聚体中氢键强度的影响

使用MP2方法研究了氢键三聚体中N-H…O=C氢键强度,探讨了氢键受体分子中不同取代基对N-H…O=C氢键强度的影响.研究表明,不同取代基对氢键三聚体中N-H…O=C氢键强度的影响是不同的:取代基为供电子基团,氢键键长r(H…O)缩短,氢键强度增强;取代基为吸电子基团,氢键键长r(H…O)伸长,氢键强度减弱.自然键轨道(NBO)分析表明,N-H…O=C氢键强度越强,氢键中氢原子的正电荷越多,氧原子的负电荷越多,质子供体和受体分子间的电荷转移越多.供电子基团使N-H…O=C氢键中氧原子的孤对电子n(O)对N-H的反键轨道σ~*(N-H)的二阶相互作用稳定化能增加,吸电子基团使这种二阶相互作用稳定化能减小.取代基对与其相近的N-H…O=C氢键影响更大.