鲍林的化学键理论的思想起源

化学键是化学与物理学于20世纪早期产生交融的重要问题,其中以美国化学家鲍林在30年代提出的价键理论最有影响力。该理论同时具有化学和物理学的多个思想来源,从19世纪后期的经典结构化学直到当时刚诞生的量子力学,以及路易斯化学键理论、X射线晶体学和物理化学。物理学比化学的影响更广,但两种来源都注重实验,演化历程中理论向实验靠拢的程度更大。     

Visual valence bond rules for chemical reactions

A symmetry-adaptation rule of the valence bond structure for concerted reactions was developed within the bonded tableau valence bond formalism. According to a symmetry analysis of the valence bond structure segments accounting for the reaction, one can predict whether a chemical process is favored or unfavored. This method is based on conceptual resonance theory and the visual valence bond approach, without carrying out any explicitly theoretical calculations to know orbital details. Furthermore, by imposing a phase factor on each bonding pair, namely, the phase alternation postulate, the mechanisms of the concerted reactions can be easily outlined. These rules have been applied to organic and inorganic reactions including the participation of biradicals and species with multi-reference character. Received: 7 September 1998 / Accepted: 9 November 1998 / Published online: 1 February 1999     

Valence bond and molecular orbital studies of the A-F bond lengths in some AFn type molecules and their fluorinated cations

The results of ab initio MP2(full)/cc-pVTZ and DFT MPW1PW91/cc-pVTZ molecular orbital calculations of the bond lengths are reported for non-hypercoordinate and hypercoordinate systems of the general type AF_n^q+, with q≥0 and A = N, P, O, S and Cl. They show that except for OF₄²⁺ the bond lengths decrease as the cationic character increases. Increased-valence structures are used to provide valence bond (VB) rationalizations for the bond length shortenings. In these valence bond structures, the degree of multiple bonding increases as the cationic character increases.     

Analysis of the delocalization in the topological theory of chemical bond

The topological analysis of the gradient field of the electron localization function provides a convenient theoretical framework for the partition of the molecular space into basins of attractors having a clear chemical meaning. The basin populations are evaluated by integrating the one-electron density over the basins. The variance of the basin population provides a measure of the delocalization. The behavior of the core C(X) and protonated valence basins V(X, H) populations were investigated. The analysis of the population variance in terms of cross-contributions is presented for aromatic and antiaromatic systems, hypervalent molecules and hydrogen-bonded complexes. For hypervalent molecules this analysis emphasizes the importance of the ionic resonance structures.     

主族元素AB4型含氧酸根的成键分析——推荐一个研究型计算化学实验

介绍了一个面向高年级本科生的研究型计算化学实验。主族元素AB4型含氧酸根是无机和结构化学理论课程中讨论化学键类型的例子,然而其结果却存在争议。本实验利用常用量子化学软件,通过计算化学方法分析化学成键,验证猜测,并得出结论。旨在通过本实验,锻炼学生对量子化学计算方法的运用,进而加深对化学基础知识的理解。     

对结构化学中价键理论教学的若干思考

通过追踪原始文献,分析结构化学中价键理论部分的教学内容,特别是对氧气分子基态电子结构的处理,发现价键理论不仅能够正确解释或预测分子结构,而且对芳香性、铁磁性等化学键本质的描述表现更优.     

Reply to comment on the paper “An efficient Algorithm for Energy Gradients and Orbital Optimization in Valence Bond Theory”

van Lenthe, Broer, and Rashid made comments on our 2009 paper [Song et al., J. Comput. Chem. 2009, 30, 399] by criticizing that we did not properly reference the work by Broer and Nieuwpoort in 1988 [Broer and Nieuwpoort, Theor. Chim. Acta. 1988, 73, 405], and we favorably compared our valence bond self‐consistent field (VBSCF) algorithm with theirs. However, both criticisms are unjustified insignificant. The Broer–Nieuwpoort algorithm, properly cited in our paper, is for the evaluations of matrix elements between determinants of nonorthogonal orbitals. Stating that this algorithm “can be used for an orbital optimization” afterwards [van Lenthe et al., submitted] is not a plausible way to require more credits or even criticize others. While we stand by our statement that our algorithms scales at O(m⁴) and van Lenthe et al.'s approximate Newton Raphson algorithm scales at O(mN⁵) (here m and N are the numbers of basis functions and electrons), as we discussed in our original paper, it becomes obvious that any strict comparison among different algorithms is difficult, unproductive, and counteractive. © 2012 Wiley Periodicals, Inc.     

Analysis of the chemical bond

The energy expression of the MO-LCAO scheme is corrected approximately for the left-right correlation such that it leads to the correct dissociation limit. Together with the correlation correction a correction is applied to the interference term, whereas the sharing penetration effects are neglected. The derivation of this corrected approximate energy formula is suggested from an analysis of binding in H₂ ⁺ and H₂. The binding energy consists mainly of three contributions: interference, quasiclassical interaction, promotion. Two-electron interference contributions are absorbed into the one-electron terms. The basis dependence of the fragmentation of the binding energy is discussed and an appropriate hybrid basis is constructed. Rotational invariance is found to a high degree of accuracy. In terms of the proposed scheme the binding in several diatomic and polyatomic molecules is analysed. The individual contributions to the binding energy turn out to be physically meaningful.     

The nature of the chemical bond revisited: an energy-partitioning analysis of nonpolar bonds

The nature of the chemical bond in nonpolar molecules has been investigated by energy-partitioning analysis (EPA) of the ADF program using DFT calculations. The EPA divides the bonding interactions into three major components, that is, the repulsive Pauli term, quasiclassical electrostatic interactions, and orbital interactions. The electrostatic and orbital terms are used to define the nature of the chemical bond. It is shown that nonpolar bonds between main-group elements of the first and higher octal rows of the periodic system, which are prototypical covalent bonds, have large attractive contributions from classical electrostatic interactions, which may even be stronger than the attractive orbital interactions. Fragments of molecules with totally symmetrical electron-density distributions, like the nitrogen atoms in N(2), may strongly attract each other through classical electrostatic forces, which constitute 30.0 % of the total attractive interactions. The electrostatic attraction can be enhanced by anisotropic charge distribution of the valence electrons of the atoms that have local areas of (negative) charge concentration. It is shown that the use of atomic partial charges in the analysis of the nature of the interatomic interactions may be misleading because they do not reveal the topography of the electronic charge distribution. Besides dinitrogen, four groups of molecules have been studied. The attractive binding interactions in H(n)E-EH(n) (E=Li to F; n=0-3) have between 20.7 (E=F) and 58.4 % (E=Be) electrostatic character. The substitution of hydrogen by fluorine does not lead to significant changes in the nature of the binding interactions in F(n)E-EF(n) (E=Be to O). The electrostatic contributions to the attractive interactions in F(n)E-EF(n) are between 29.8 (E=O) and 55.3 % (E=Be). The fluorine substituents have a significant effect on the Pauli repulsion in the nitrogen and oxygen compounds. This explains why F(2)N-NF(2) has a much weaker bond than H(2)N-NH(2), whereas the interaction energy in FO-OF is much stronger than in HO-OH. The orbital interactions make larger contributions to the double bonds in HB=BH, H(2)C=CH(2), and HN=NH (between 59.9 % in B(2)H(2) and 65.4 % in N(2)H(2)) than to the corresponding single bonds in H(n)E-EH(n). The orbital term Delta E(orb) (72.4 %) makes an even greater contribution to the HC triple bond CH triple bond. The contribution of Delta E(orb) to the H(n)E=EH(n) bond increases and the relative contribution of the pi bonding decreases as E becomes more electronegative. The pi-bonding interactions in HC triple bond CH amount to 44.4 % of the total orbital interactions. The interaction energy in H(3)E-EH(3) (E=C to Pb) decreases monotonically as the element E becomes heavier. The electrostatic contributions to the E-E bond increases from E=C (41.4 %) to E=Sn (55.1 %) but then decreases when E=Pb (51.7 %). A true understanding of the strength and trends of the chemical bonds can only be achieved when the Pauli repulsion is considered. In an absolute sense the repulsive Delta E(Pauli) term is in most cases the largest term in the EPA.     

Vibrational energies,bonding nature,electronic properties,spectroscopic investigations and analysis of 3-bromo-4-Chlorobenzophenone

In this present study, we investigated pharmaceutically active of 3-Bromo-4-chlorobenzophenone. Structural, electronic properties (HOMO-LUMO, MEP) are investigated using DFT tool. Vibrational spectral analysis for FT-IR and FT-Raman are made of headline molecule. Electronic transition properties are discussed with the help of UV–Vis spectral analysis. Biologically active sites are found from MEP analysis. Electron delocalization properties are studied explored from HOMO-LUMO band gap energy. Moreover, intra molecular interactions are explained from NBO method. Molecular docking studies are performed to find the interactions various pathologies. The topological properties of the electron density have been analyzed.     

A molecular orbital explanation of bond distance variation caused by hydrogen bond formation

For hydrogen bond systems X–D–HA–Y, a simple molecular orbital model is proposed to understand the mechanism of the bond distance variations caused by the hydrogen bond formation. This model explains the bond distance variations for X–D and A–Y as follows. Electrostatic potential that the electrons in a molecule receive from other molecules causes the changes in atomic orbital energy differences between the bonded atoms. Then, the changes in the orbital energy differences make the bond orders larger or smaller and consequently the bond distances vary. The validity of this model has been confirmed by the effective fragment potential method, using the test systems of (HCOOH)₂, HCONH₂ (formamide) crystal and BF₃·2H₂O crystal.     

Factors determining bond angles from a classical valence bond perspective. Covalent structure of H2O

We identify the energy contributions that govern the interorbital and internuclear angles in the classical covalent structure of H₂O. The central atom valence state term plays a primary role in H₂O and other AH₂ molecules as well. Lone pair interactions of three different types are also of major significance.On leave 1977–78 at the University of California, Santa Barbara     

Origin of cis preference among the three isomers of 1,4‐difluorobutadiene

The slight energy differences among the three isomers of 1,4‐difluorobutadiene have been investigated by Gaussian‐3 (G3) theory. The computational results suggest that the Gaussian‐3–Becke's three‐parameter functional (G3B3) theoretical estimates are in good agreement with experimental data. Mulliken population analysis also has been performed to interpret the anomalous equilibrium relationship among these three isomers. Wire mesh contours of the highest occupied molecular orbital (HOMO) orbitals of these isomers help to illustrate the cis effect visually. Natural bond orbital (NBO) analysis indicates that the origin of cis preference among the three isomers may lie in the configurational orientation and the n‐π conjugative interaction between fluorine atom and C?C double bond. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003     

A model of the chemical bond must be rooted in quantum mechanics, provide insight, and possess predictive power

In this response to the preceding paper by Bader, we show that the core arguments and statements presented in the latter are flawed. We argue that it is insufficient for a model of the chemical bond to be rooted in quantum mechanics. A good model must in addition provide insight and possess predictive power. Our molecular orbital (MO) model of the chemical bond, in particular, the associated energy-decomposition approach satisfies all these conditions. On the other hand, Atoms-in-Molecules (AIM) theory is only rooted in quantum mechanics as far as its mathematical framework is concerned. The physical status of its central concepts is not so clear. In particular, "bond paths" and "bond critical points" are once more confirmed not to be indicators of a stabilizing interaction. Moreover, AIM theory lacks any predictive power. We also address specific questions raised in the preceding paper. Finally, interpreting chemical bonding implies choosing a perspective on this phenomenon. That there are many perspectives is a matter of fact and this is in no way unphysical. What is unscientific is to claim uniqueness and truth for one of these choices, namely AIM, and to dismiss on this ground all other approaches.     

Natural bond orbital analysis of some S‐nitrosothiols biological molecules

Theoretical study of several S‐nitrosothiols biological molecules has been performed using quantum computational ab initio RHF and density functional B3LYP and B3PW91 methods with 6‐31G(d,p) basis set. Geometries obtained from DFT calculations were used to perform natural bond orbital (NBO) analysis. It is noted that the weakness in the S? N sigma bond is due to n_O1→σ delocalization and is responsible for the longer S? N bond length in S‐nitrosothiols. It is also noted that decreased occupancy of the localized σ_SN orbital in the idealized Lewis structure or increased occupancy of σ of the non‐Lewis orbital, and their subsequent impact on molecular stability and geometry (bond lengths) are related with the resulting p character of the corresponding sulfur natural hybrid orbital of σ_SN bond orbital. In addition, the charge transfer energy decreases with the increasing of the Hammett constants of substituent groups, and the partial charge distribution on the skeletal atoms shows that the electrostatic repulsion or attraction between atoms can give a significant contribution to the intramolecular and intermolecular interaction. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010     

Experimental evidence and bond characterization of a cyclopropenylgermylene

The reduction of p-anisyl(1,2,3-tri-tert-butylcycloprop-2-en-1-yl)dichlorogermane (1) with potassium in the presence of an excess of tert-butyldimethylsilane in benzene under reflux gave p-anisyl(tert-butyldimethylsilyl)(1,2,3-tri-tert-butylcycloprop-2-en-1-yl)germane (4) in 15% yield. The formation of 4 indicates that p-anisyl(1,2,3-tri-tert-butylcycloprop-2-en-1-yl)germylene (2), which is the first example of a (cycloprop-2-en-1-yl)germylene derivative, was generated and trapped by the hydrosilane. The DFT calculations revealed that the cis-2-p-anisyl-1,3,4-tri-tert-butyl-2-germabicyclo[1.1.0]butane-2,4-diyl structure cis-5 is 8.0 kJ/mol more stable than cis-2. The NBO analysis revealed that cis-5 has a 2-germabicyclo[1.1.0]butane diradical character.     

量子化学奠基人之一——查尔斯.阿尔弗雷德.库尔森

查尔斯·阿尔弗雷德·库尔森是量子化学领域的杰出研究者,也是“英国量子化学学派”的领导者。他将分子轨道理论应用于化学键、分子电子结构和分数价概念,并发展了许多数学技术来解决化学和物理问题;他的著作《原子价》被认为是用于量子化学教学的杰作。库尔森无疑为提升量子化学在当今化学中的作用做出了巨大贡献。本文就库尔森的生平、求学经历及其对量子化学的贡献进行了论述。