二氧化氮分子中的化学键

二氧化氮分子中的化学键张小平李夏＊邹应泉（北京铁路师范学校１０００３１）（首都师范大学化学系１０００３７）（北京师范大学化学系１００８７５）我们曾经利用半经验方法讨论过Ｎ２Ｏ４的结构问题［１］。最近，具有奇数电子的角形结构的ＮＯ２分子又引起了我们极大...     

A^NB^8—N晶体中的化学键参数与硬度的关系

物质的硬度作为一个物理量已被广泛运用于各种研究领域。硬度测量在各种机械试验法中是最迅速、最经济的一种方法,而且材料硬度值与其它机械性能有一些相当精确的相应关系。有关硬度的各种测试方法已发展相当完善。同时,人们对硬度的微观机制也曾作了许多     

B2H6分子中的化学键

在结构化学的教学中,常常要讨论二硼烷(B2H6)等“缺电子分子”的几何结构和化学键的性质.二硼烷的几何结构已早有定论,因为无论是它的化学性质,还是包括电子衍射、核磁共振、X-射线在内的广泛物理化学研究,都表明两个硼原子与四个端氢原子共平面,另外两个氢原子在平面的上下(如图所示).而且,该分子结构中存在三中心双电子化学键也为大家普遍接受.然而,关于B2H6分子中三中心化学键的解释在教科书中却各持己见,甚至同一本书中有两种不同的观点[1].     

Hellmann-Feynman定理在化学键研究中的应用

恩格斯说:“一切化学过程都归结为化学的吸引和排斥的过程”。(《马克思恩格斯全集》20卷553页)化学运动最基本的物质单位是原子。在一定条件下原子间相互吸引化合为分子;分子中的原子又相互排斥,在一定条件下分解为原子。如此吸引、排斥的不断进行,就形成了化学运动过程。在化合和分解的矛盾运动中,存在着化学键的断裂和     

以BH^—4为配体的金属配合物中的多中心化学键

一、前言以BH_4~-为配体与金属离子(M~(n+))所形成的配合物具有独特的电子结构和化学性质,在有机合成、高分子聚合等方面具有重要的应用价值。研究它的结构和化学键无论在理论上还是在实践上都具有重要的意义。这类化合物是当前无机和金属有机化学家比较感兴趣的课题之一,也是当前金属有机化学方面比较活跃、发展较快的领域之一。     

高岭石—金—硫系列的化学键与稳定性研究

用密度泛函离散变分计算方法（ＤＦＴ－ＤＶＭ）,研究了高岭石、高岭石－金和高岭石－金－硫系列,讨论了结构,化学键与稳定性之间的关系。选用了不含金及金或金－硫原子团位于不同方位的多个模型。计算结果表明,金位于层状高岭石侧面的模型比金位于上、下面更为稳定,在金位于层状高岭石侧面的情况下,金靠近铝的模型比金靠近铝空位更为稳定,高岭石－金－硫体系中的金－硫原子团比高岭石－金体系中的更容易被高岭石吸附。模型间     

破坏化学键的新方法

想要破坏化合物中的特定键结吗？试试直接拉断它。对化学家而言，为了完成他们所想要完成的反应，总是会对化合物利用各种方法来增加反应物的反应速率。方法有加热、通电、或是加入各式各样的催化剂。有时则是希望可以把反应物不需要的部分通过打断键结的方式拆下来，以利于实验进行。当然没有办法用镊子一个一个把键结夹断，不过Jeffrey Moore的新方法似乎更为直接，他所提出的构想是利用应力来将化合物中的特定键结拉断。     

Mitsunobu反应在构建化学键中的研究进展

Mitsunobu反应是醇与酸性化合物偶联形成新化学键的一种有效方法,可以用来构建碳-氧、碳-氮、碳-硫及碳-碳等化学键,在天然产物和功能有机分子的合成中已得到了非常广泛的应用.对Mitsunobu反应的机理及其在构建化学键中的应用进行了介绍,并对该反应的区域选择性进行了较为系统的总结.     

化学键分散剂在PZN-PZT浆料中的分散性研究

利用异丙醇钛与长链羧酸合成了一种化学键分散剂,采用沉降实验及FT-IR技术研究了该分散剂在PZN-PZT浆料中的分散性能.结果表明,该分散剂在PZN-PZT浆料中具有良好的分散性,浆料体系达到稳定状态时所需的分散剂量对应分散剂在颗粒表面上呈单分子层成键状态,分散剂分子与颗粒表面上的羟基发生化学反应,导致二者之间呈较强的化学键结合状态,从而有力地改善了PZN-PZT浆料中的分散性、均匀性.     

化学键的量子化学研究

利用量子化学方法计算N2O4分子的结构、N-N键键级及键鞍点处的电荷密度,形象直观的说明了N2O4分子中N-N键键长较长的原因.     

Electronegativity and hardness in the chemical approximation

The chemical electronegativity of an atom (Mulliken definition) has been identified with the average value of χ, the electronegativity function given by the rigorous density functional theory. An appropriate definition of hardness is developed, and a scale of hardness for bonded atoms is proposed. The electrodynamical atom model is demonstrated to produce a simple relation between atomic hardness and size. Electronegativity has been calculated for bonded atoms in a variety of molecules and crystals, covalent and ionic, without any specific approximation for the energy function E(q). Expressions for the electronegativity of a molecule have been derived and critically discussed.     

Sequential peptide chemical ligation by the thioester method and extended chemical ligation

The sequential chemical ligation of peptide thioesters by a combination of the thioester method and extended chemical ligation using a photoremovable auxiliary, 2-mercapto-1-(2-nitrophenyl)ethyl group, is described. The thiazolidine ring was used as a protecting group for the N-terminal 1,2-aminoethanethiol moiety of the auxiliary in the middle peptide thioester. After the first thioester coupling, the thiazolidine ring was opened by treatment with O-methylhydroxylamine. Second coupling by extended chemical ligation followed by UV irradiation gave the target polypeptide.     

Internal stresses and chemical binding in the H molecule

Following an interpretive formalism presented earlier, chemical binding in the H molecule has been studied in terms of the variations, with respect to R, of electrostatic field and stress components at five selected points on the interuclear axis. At three points phenomena analogous to those recorded earlier for H₂ have been observed. In particular, the existence of extremal relationships for the difference density field and the total field, as well as for the corresponding stresses, at R ? R_eq for certain specific points on the internuclear axis has been confirmed. As in the case of H₂, chemical binding in H occurs due to local variations of electrostatic pressure from point to point in such a manner as to cause the vanishing of either the total electrostatic force density or the difference force density at certain points on the internuclear axis.     

Nanotomography in the chemical, biological and materials sciences

Nanotomography is a technique of growing importance in the investigation of the shape, size, distribution and elemental composition of a wide variety of materials that are of central interest to investigators in the physical and biological sciences. Nanospatial factors often hold the key to a deeper understanding of the properties of matter at the nanoscale level. With recent advances in tomography, it is possible to achieve experimental resolution in the nanometre range, and to determine with elemental specificity the three-dimensional distribution of materials. This critical review deals principally with electron tomography, but it also outlines the power and future potential of transmission X-ray tomography, and alludes to other related techniques.     

Authority and authorship in the method of chemical nomenclature

The 1787 Method of Chemical Nomenclature jointly authored by Guyton de Morveau, Lavoisier, Berthollet and Fourcroy displays a particularly authoritarian approach to nomenclature reform in chemistry. This paper explores the basis for this authority, analysed in institutional and philosophical terms. By comparing this reform to the 1782 proposal by Guyton, we see how a consensual approach was put aside for this more authoritarian one, with Lavoisier offering the naturalised empiricist philosophy of Condillac as justification. Nevertheless, I argue that the basis for the authority of the reform remained the Academy of Sciences, the central scientific institution in ancien régime France. I also explore French commentaries on the reform to show how the approach was perceived by the scientific community both inside and outside the Academy of Sciences.