电负性均衡

电负性是分子中一个原子把电子拉向它自身的能力,是化学理论的基本概念之一。继Pauling建立第一个电负性标度后,提出了众多的电负性标度。只是在密度泛函理论的基础上,电负性概念和电负性均衡原理,才被精密地论证。近二十多年来,电负性理论的重要发展是:应用电负性均衡模型或方法,可以快速地计算分子体系的电荷分布,从而确定分子的其他性质,甚至包括分子的结构和反应性指标。通常的电负性均衡方法只把分子划分到原子区域,虽然简单直观,但其精度和应用范围受到限制。原子与键电负性均衡方法,把分子划分到包括原子区域、化学键区域和孤对电子区域,能够较快速精密地计算分子的电荷分布和其他性质,并被应用到构建新一代可极化或浮动电荷力场的探索中,有广阔的应用前景。     

DFT study on the effect of relative positions of methyl-, nitro- and N→oxide groups on the molecular structure,thermal/kinetic stability,crystal density,heat of decomposition and performance characteristics of triazolones

Methyl-, nitro- and N→oxide substituted triazolones are of interest in the contest of high-energy density compounds and have been found to have true local energy minima at the B3LYP/aug-cc-pVDZ level. The optimised structures, harmonic frequencies and thermodynamic values for all the model molecules have been obtained in their ground state. The velocity of detonation (D) and detonation pressure (P) have been evaluated by the Kamlet–Jacob equations using the crystal density and the heat of explosion. The estimated performance properties are higher (D = 9.92–10.27 km/s, P = 48.10–52.52 GPa) compared with 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (D = 9.20 km/s, P = 42.0 Gpa). The higher densities are possibly due to the intramolecular hydrogen bonds and the layered structures in the crystal lattice. We speculate that the calculated heat of explosion and the density are for the gas phase compounds and in the reality they should be for the solid phase which would diminish the magnitude of the calculated values. The –N→O and –NO₂ group leads to the desirable consequences of higher heat of explosion and diminished sensitivities. The substituting of N–H hydrogen atom(s) of triazolones for a –CH₃ group decreases melting point, heat of formation and density; however, the methyl group increases the thermal stability.     

Electronegativity Scaled as a Average Attracting Energy of Valence‐Shell Electrons in a Ground‐State Free Atom

The total capability of an atom attracting valence electrons can be measured by the sum of ionization energies of valence electron in a ground‐state free atom plus its electron affinity called Total Attracting Energy, TAE = Σn_iE_i + EA, where, E_i is the ionization energy of the ith valence‐shell electron in a ground‐state free atom, n_i is the number of valence‐shell electron bearing energy E_i, and EA is the electron affinity. And the electronegativity χ_CL is proportional to the average of TAE, AAE = TAE_av, divided by Σn_i, the number of atomic valence‐shell electrons. χ_CL = 0.1813 TAE_av = 0.1813 AAE = 0.1813 TAE/Σn_i, = 0.1813 (Σn_iE_I + EA)/Σn_i. Further, the atomic valence orbital electronegativity can be also obtained from the TAE value of an atom. Some discussions were made on several special aspects such as scale of rare gases, comparisons with Pauling's and Allen's scales, etc.     

应用ABEEM模型计算铁(Ⅱ)配合物的电荷分布

以密度泛函理论和电负性均衡原理为基础,在原子-键电负性均衡模型中,利用最小二乘法,并结合自编程序,拟合确定了氢、碳、氮、硫以及铁(Ⅱ)等各种类型的原子及相关化学键区域的参数.利用上述参数计算了一些铁(Ⅱ)配合物的电荷分布,计算结果可以和从头算结果很好地相关联.     

烷烃加和型性质的拓扑同系递变规律研究

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拓扑指数ND, 它对分子结构实现唯一性表征, 具有优良的结构选择性, 用ND指数对链烷烃的加和型性质及同系递变规律进行研究, 结果表明烷烃加和型性质P可用下式来定量描述: P＝aND₁＋bND₂＋cND₃＋d, 其中a, b, c, d为常数. 用该式对85种链烷烃的标准生成焓Δ_fH^ө_m, 标准熵Δ_fS^ө_m, 标准生成吉布斯自由能Δ_fG^ө_m及67种链烷烃的摩尔体积V_m, 摩尔折射度R_m进行预测, 预测值与实验值吻合良好.     

原子价壳层电子量子拓扑指数与元素电负性的关系

在基态原子价壳层电子隐核图的基础上, 基于拓扑化学原理以及原子价壳层电子结构特征, 构建了原子价壳层电子量子拓扑指数(AEI), 它对基态原子实现唯一性表征, 结合原子价壳层电子平均化能(∑n_iE_i/∑n_i)等参数, 建立了一套新的元素电负性标度: X_N＝－0.588710AEI₁＋0.761214AEI₂＋0.154982(∑n_iE_i/∑n_i)－0.080929. 该式给出了周期表中氢至镅共95种元素的电负性, 结果表明新电负性标度X_N与Pauling电负性标度颇为一致. 进一步从原子价轨道量子拓扑指数确定了sp, sp², sp³杂化轨道的电负性. 新标度在元素和物质的结构-性质研究中具有一定的适用性.     

AEIV结合AHSI用于饱和脂肪酮类物质的13C NMR谱模拟

应用一种反映分子局部微环境描述子--原子电性相互作用矢量（vector of atomic electronegative interaction,AEIV）和原子杂化状态指数（Atomic Hybridation State Index, AHSI）对饱和脂肪酮类化合物的55种分子中的153个¹³C NMR谱建模模拟,应用多元线性回归方法得到定量结构波谱关系(QSSR)模型的复相关系数R_MM=0.997, 标准偏差为SD_MM=7.155. 采用留一法交互检验的结果是R_CV=0.993,SD_CV=10.195. 并随机抽出三部分分子进行检验,得到的相关系数分别是R_MM1=0.996,R_MM2=0.996,R_MM3=0.999. 研究结果表明使用AEIV和AHSI所建模型预测能力是相当稳定的.     

基于人工神经网络研究芳胺喹唑啉衍生物的抗胃癌活性

基于分子电性距离矢量(M1)表征21个芳胺喹唑啉衍生物的分子结构,并与其对人胃癌细胞的抗癌活性(pI)关联.通过最佳变量子集回归方法建立上述化合物抗胃癌活性的三参数(M15、M18、M82)定量构效关系模型.其交叉验证系数(R2cv)、非交叉验证系数(R2)依次为0.386和0.737.通过R、R2cv.、VIF等检验...     

从静电作用探讨化学键的本质及其教学实践

当前中学的化学键教学中，过分强调Lewis“八隅体结构”，忽视静电作用力，导致学生不能认识到化学键的本质，且传统教学方法中，元素的二分法导致化学键的二分法，不利于学生思维的发展。借鉴国外相关研究，在考虑学生认知水平的基础上，尝试从强调化学键静电作用的本质和引入电负性的角度设计教学内容，帮助学生构建正确的化学键本质观。     

High resolution magic angle spinning NMR studies of31P and11B in fast ion conducting AgI-Ag2O-P2O5 and AgI-Ag2O-B2O3 glasses

Silver iodide-based fast ion conducting glasses containing silver phosphate and silver borate have been studied. An attempt is made to identify the interaction between anions by studying the chemical shifts of³¹P and¹¹B atoms in high resolution (HR) magic angle spinning (MAS) NMR spectra. Variation in the chemical shifts of³¹P or¹¹B has been observed which is attributed to the change in the partial charge on the³¹P or¹¹B. This is indicative of the change in the electronegativity of the anion matrix as a whole. This in turn is interpreted as due to significant interaction among anions. The significance of such interaction to the concept of structural unpinning of silver ions in fast ion conducting glasses is discussed. Communication number 593 from Solid State and Structural Chemistry Unit