对"计算多环有机物中环数的捷径"一文的商榷

贵刊在 2 0 0 1年第 2期 41页刊载了“计算多环有机物中环数的捷径”一文。笔者认为原文中介绍的计算公式有误 ,就算修正之后没有误也不是什么捷径。在此想与原文作者商榷 ,请同行们指教。原文中计算公式为 :r=1 +1 / 2t+q………… (1 )式中r为环数 ,t为三级碳原子 (CH)数 ,q为四级碳原子 (C)数。按公式 (1 )需要知道三级碳原子、四级碳原子的数目才能计算出环数的结果。条件是只适用于不含任何取代基或功能团的饱和烃。笔者认为这个公式应修正为 :r=2 +1 / 2t+q………… (2 )也就是将原公式中 1改为 2 ,其计算结果才应多一个环才对。修正…     

系列苯炔化合物和苯炔树枝大分子的合成及其光学性质的研究

合成了一系列苯炔化合物, 并对它们的紫外吸收和荧光发射性质进行了研究. 通过HOMO和LUMO轨道能量差ΔE、分子轨道图及相关碳原子上的电荷密度讨论了分子结构和大小对这些化合物紫外吸收和荧光发光性质的影响. 在间位苯炔化合物及间位苯炔树枝大分子(dendrimer)中, 紫外吸收峰不随苯炔分枝数和dendrimer阶数增加而红移, 共轭被中心苯环隔断. 而在邻或对位取代的苯炔化合物中, 共轭则不受中心苯环的影响而延伸至整个分子. 其原因可能和中心苯环上与苯炔分枝相连的碳原子的电荷密度有关. 在激发态下, 间位苯炔化合物中苯炔分枝间存在耦合作用, 荧光发射随苯炔分枝数增加而红移. 但这种耦合作用只发生在与同一苯环相连的分枝间, 因此荧光发射不随dendrimer阶数增加而红移.     

从13C化学位移分析取代基的诱导效应、共轭效应和亲电取代反应活性间的关系

以单取代苯为模型,建立并论证了取代基诱导效应参数RI、共轭效应参数RC及诱导和共轭共同作用效应参数R,RI=128.5-δ1,RC=642.5-∑6n=2δn,R=771-∑6n=1δn,δn(n=1～6)是单取代苯苯环上6个碳原子Cn(n=1～6)的化学位移,δ1是取代位C1的化学位移,128.5为苯的13C化学位移。当参数R>0时,取代基对苯环有给电子效应。一般而言,RI<0、RC>0、R>0时,取代基是典型的使苯环活化的邻对位定位基;RI<0、RC<0、R<0时,取代基是使苯环钝化的间位定位基;其余情况参考δn的具体数值判定取代基的作用。能与苯环形成最佳共轭的基团,其与苯环直接相连的是与碳原子同周期的B、C、N、O、F。     

硅苯和锗苯与2,3-二甲基丁二烯杂Diels-Alder反应的理论研究

采用密度泛函理论(DFT)方法在B3LYP/6-311G(d,p)水平上研究了硅苯和锗苯与2,3-二甲基丁二烯的两类杂Diels-Alder反应的微观机理、势能剖面、取代基效应和溶剂效应.计算结果表明,所研究反应均以协同非同步的方式进行,且C—Si或C—Ge键总是先于C—C键形成.在硅苯或锗苯分子作为杂亲二烯体的[2+4]反应中,endo进攻方式的非同步性比exo进攻稍大一些,而后者比前者一般要稍稍有利一些.在硅苯或锗苯分子作为杂二烯烃的[4+2]反应中,反应非同步性的大小与产物中不对称的亲二烯体上的取代基与硅或锗原子之间的相对位置有关,且在动力学上总是非同步性较大的反应更容易进行一些.硅或锗原子上的CCl3或NH2取代基在热力学和动力学上一般有利于反应的进行,而C(CH3)3取代基的影响则相反.[2+4]反应在热力学和动力学上均远比相应的[4+2]反应容易进行,这与实验完全一致.苯和甲醇溶剂对所研究反应的势能剖面影响较小.     

锡苯和铅苯二聚反应的理论研究

采用密度泛函理论B3LYP方法,研究了锡苯和铅苯的[2+2],[4+2]及[4+4]二聚反应的微观机理和势能剖面,考察了Sn(Pb)原子上的2,4,6-三甲基苯基(Mes)取代基对反应势能剖面的影响.研究结果表明,所有反应均为协同过程,且大多数情况下,2个C—Sn(Pb)键同步形成.[2+2]和[4+2]反应在热力学和动力学上均比相应的[4+4]反应容易进行,而[4+2]反应在动力学上比相应的[2+2]反应有利.Sn(Pb)原子上的Mes取代基在热力学和动力学上均不利于反应的进行.铅苯的动力学稳定性与锡苯相当,但其热力学稳定性高于锡苯.     

聚合硫化碳的稳定性和聚合活性

聚合硫化碳是集分子自组装、聚合硫化碳导体和半导体、非线性光学、化学活性中间体等多功能于一体的一类新型无机物.根据分子结构演变规律,在MPW1PW(91)/(6)-311G(d)水平上,设计CmSm+22-系列硫化碳分子的结构,计算其电子性质,得到了分子稳定化能与碳原子数之间所服从的线性关系,其中相关系数γ=0.9995,即每增加一个C2S2单元,稳定化能按线性关系ES=–0.221479–0.337059m降低,据此预测了部分聚合分子属稳定的聚合体.经原子轨道NBO布居数和共振结构计算分析,共轭π轨道的存在,是硫化碳聚合体稳定存在的原因,也是分子自组装、导电功能的结构基础.两端C2S2结构单元的化学活泼性和负电性预示,CmSm+22-硫化碳分子具有进一步聚合的活性,其独立负离子也易与各种基团结合形成稳定的化合物.     

一个新的连接性指数用于脂肪醇QSPR/QSAR研究

本文提出了一个计算分子中成键原子点价δzi的新方法,其公式为:δzi=Zi(Zi-hi)Vi/Ei/n2i式中,ni,Zi分别为原子i的核外电子层数和价电子数,hi为与原子i直接相连的氢原子数,Vi,Ei分别为分子图中原子i的顶点度和边度.     

卤代苯的沸点与分子结构的定量关系

原子点价是分子连接性指数的核心概念.本文提出了一个计算原子点价δiz'的新方法,其公式为: δiz'=mi(Zi-hi)Vi/Ei/ni2(1) 式中,ni,mi,Zi分别是原子i的核外电子层数、成键电子数和价电子数,hi是与原子i直接相连的氢原子数,Vi,Ei分别是分子图中原子i的顶点度和边度.     

渤海稠油及其组分中杂原子化合物的负离子电喷雾-高分辨质谱分析

采用沉淀法和色谱分离法将渤海某油田稠油分离成沥青质、胶质、剩余分3个组分。采用负离子电喷雾技术(ESI)结合高分辨傅立叶变换离子回旋共振质谱仪(FT-ICR MS)研究了该稠油及各组分的分子组成。结果表明,剩余分中有较少的极性杂原子化合物能被负离子ESI电离,如N_1,N_1O_1,O_1和O_2类,其等效双键数(DBE)较小。胶质和原油中极性化合物有相同的杂原子类型,包括N_1,N_1O_1,N_1O_2,N_2,N_2O_2S_1,O_1,O_2,其中胶质和原油中N_1,O_1,O_2类化合物的DBE-碳数分布图相似。沥青质中富集高缩合度且多杂原子的酸性化合物,如含杂原子N_,S的氧化程度高的化合物(N_2O_1,N_1O_3,S_1O_3)及O_3类化合物,这些物质具有较高的界面活性,易吸附在界面上促进界面张力降低和增强界面膜强度,从而有利于乳状液稳定存在。N_1O_1,N_1O_2,N_1O_3类化合物,N_2O_1类化合物可能分别是N_1化合物,N_2化合物的氧化降解产物;随着氧化降解程度增加,降解产物的极性明显增强。     

端基对二噻吩和苯并噻吩类共轭桥化合物电子结构及载流子传输性能的影响

采用密度泛函理论(DFT, TDDFT) B3LYP/6-31G(d)和PBE0/6-31G(d)方法对苯乙烯/乙炔为端基, 二噻吩(2T)、苯并二噻吩(TPT)和二苯并噻吩(PTP)为共轭桥的12个化合物进行了系统地计算研究. 在分别优化中性态与离子态几何构型的基础上, 获得了前线轨道能级、电离能(IPs)、电子亲合能(EAs)、重组能(λ_h/λ_e)和电子吸收光谱等信息. 结果表明, 苯乙炔基取代苯乙烯基对LUMO能级影响很小, 但HOMO能级明显降低, 能级差?E和激发能E_v增大, 吸收光谱蓝移10～30 nm, 多数苯乙炔基化合物的重组能均有所降低|端基相同共轭桥分别为2T, TPT和PTP时, HOMO能级逐渐降低, LUMO能级逐渐升高, ?E和E_v依次增大, 吸收光谱依次蓝移30～45 nm. 研究结果还表明, TPT共轭桥化合物的重组能较小, 且λ_h与λ_e相近, 有利于载流子传输平衡, 提高传输速率. 本文设计的苯乙炔基苯并二噻吩(DPATPT)有望成为潜在的传输效率高、抗氧化能力强的载流子传输材料.     

Diborane Concatenation Leads to New Planar Boron Chemistry

Diborane has long been realized to be analogous to ethylene in terms of its bonding MOs, both as to symmetries and splitting patterns. This naturally suggests an investigation to see whether other similar conjugated hydrocarbons manifest a similar boron-substituted and H₂ supplemented borane. That is, for a conjugated hydrocarbon structure with a neighbor-paired resonance pattern, we propose to look at boranes where each carbon atom is replaced by a boron atom, and an H-atom pair is added to each double bond of the resonance structure, with one H above the molecular plane and one below. This construction of concatenated diboranes is uniformly different than that for the previously known stable boranes of 4 or more B atoms. We find from quantum-chemical computations that our so constructed polyboranes are stable. All this suggests a possible novel new chapter in borane chemistry – a chapter with some promise of understandings related to that for (alternant) conjugated hydrocarbons.     

Statistical properties of carbon nanostructures

We look at modeling carbon nanostructures from a theoretical graph network view, where a graph has atoms at a vertex and links represent bonds. In this way, we can calculate standard statistical mechanics functions (entropy, enthalpy, and free energy) and matrix indices (Wiener index) of finite structures, such as fullerenes and carbon nanotubes. The Euclidean Wiener index (topographical index) is compared with its topological (standard) counterpart. For many of these parameters, the data have power law behavior, especially when plotted versus the number of bonds or the number of atoms. The number of bonds in a carbon nanotube is linear with the length of the nanotube, thus enabling us to calculate the heat of formation of capped (5,5) and (10,10) nanotubes. These properties are determined from atomic coordinates using MATLAB routines.     

Benzenoid rings resonance energies and local aromaticity of benzenoid hydrocarbons

In this article, we consider partitioning of the analytical expression for resonance energy (RE) in smaller benzenoid hydrocarbons, to individual benzenoid rings of polycyclic molecules. The analytical expression for molecular RE, available since 1976, is given by the count of all linearly independent conjugated circuit in all Kekulé structures in a molecule. Analytical expression for local ring RE (RRE) is given by counting all linearly independent conjugated circuits involving single benzenoid ring in all Kekulé structures, which when added, gives the molecular RE. If for benzene ring the RRE is taken to be 1.000, rings in polycyclic benzenoid hydrocarbons have their ring RRE, which give the degree of their local aromaticity, smaller than 1.000. The difference to 1.000 is a measure of the similarity of a ring to benzene in this one-dimensional (1-D) representation of local aromaticities of benzenoid hydrocarbons. The plot of RRE against the distance of the same ring from benzene in the Local Aromaticity Map, in which benzenoid rings are characterized ring bond orders and average variations of adjacent CC bonds, shows linear correlation (with r = 0.91), reducing the local aromaticity in benzenoid hydrocarbons to 1-D molecular property. © 2018 Wiley Periodicals, Inc.     

Additivity of resonance energy in benzenoid hydrocarbons

A simple method is described for the calculation of resonance energies (RE ) of linear acenes based on their number of Kekulé structures. The values obtained for the first five linear acenes are used to graph–theoretically calculate RES of a wide variety of benzenoid hydrocarbons. Excellent linear relationships are found between RES and each of A-II, graph-theoretical (GT ), Hess–Schaad (HS ), and Dewar resonance energies (SCF ). These relations apply to 42 hydrocarbons and lead to the following equations: A-II = 0.084RE + 0.080 (0.9999); GT = 0.072RE + 0. 135 (0.9832); HS = 0. 106RE + 0. 169 (0.9889); and SCF = 0.316RE + 0. 166 (0.9899). Correlation coefficients are shown in parentheses. A linear relation also exists between RES and the square roots of the wavelengths of the UV spectra of hydrocarbons of the linear acenes and phene series. Least-squares analysis of the data leads to the following equation: RE = 0.412(λ)^½ ?15.479, with a correlation coefficient equal to 0.9903, in which λ is the wavelength of the β band of the UV spectra of these hydrocarbons. The method predicts no resonance energies for both open chain polyenes and the radialenes.     

The prevalence of isocloso deltahedra in low-energy hypoelectronic metalladicarbaboranes with a single metal vertex: manganese and rhenium derivatives

Theoretical studies on the hypoelectronic metalladicarbaboranes CpMC(2)B(n-3)H(n-1) (M = Mn, Re; n = 9, 10, 11) having 2n skeletal electrons indicate that true isocloso MC(2)B(n-3) deltahedra are highly energetically favored in which the metal atom occupies the single degree 6 vertex. This contrasts with the previously studied isoelectronic diferradicarbaboranes Cp(2)Fe(2)C(2)B(n-3)H(n-1) for which the isocloso structure is clearly favored only for the 10-vertex system. For the 12-vertex hypoelectronic manganadicarbaborane CpMnC(2)B(9)H(11) with 2n (= 24) skeletal electrons the lowest energy structures have central MnC(2)B(9) icosahedra. However, for the corresponding rhenadicarbaborane CpReC(2)B(9)H(11) the lowest energy structures have central non-icosahedral ReC(2)B(9) deltahedra with two degree 6 vertices, one of which is occupied by the rhenium atom. The low-energy structures for the metalladicarbaboranes studied in this work relate to the preferences of transition metal atoms for degree 6 vertices but those of boron and carbon for degree 5 and 4 vertices, respectively.     

Geometry and stability of BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters

Density functional theory B3PW91/6-31+G* calculations on BenCm (n=1-10; m=1, 2, ..., to 11-n) clusters have been carried out to examine the effect of cluster size, relative composition, binding energy per atom, HOMO-LUMO gap, vertical ionization potential, and electron affinity on their relative stabilities. The most stable planar cyclic conformations of these clusters always show at least a set of two carbon atoms between two beryllium atoms, while structures where beryllium atoms cluster together, or allow the intercalation of one carbon atom between two of them, generally seem to be the least stable ones. Clusters containing 1, 2, and 3 beryllium atoms (Be2C8, Be3C6, Be2C6, BeC6, Be2C4, BeC4, Be2C2, and BeC2) are identified as clusters of "magic numbers" in terms of their high binding energy per atom, high HOMO-LUMO gap, vertical ionization potential, and second difference in energy per beryllium atom.     

Resonance energies of large conjugated hydrocarbons by a statistical method

We developed a theoretical method for studying the aromatic stability of large molecules, molecules having a dozen and more fused benzene rings. Such molecules have so far often been outside the domain of theoretical studies. Combining the statistical approach and a particular graph theoretical analysis, it is possible to derive the expressions for molecular resonance energy for molecules of any size. The basis of the method is enumeration of conjugated circuits in random Kekulé valence structures. The method has been applied to evaluation of the resonance energies of conjugated hydrocarbons having about a dozen fused benzene rings. The approach consists of (1) construction of random Kekulé valence structures, (2) enumeration of conjugated circuits within the generated random valence structures, and (3) application of standard statistical analysis to a sufficiently large sample of structures. The construction of random valence forms is nontrivial, and some problems in generating random structures are discussed. The random Kekulé valence structures allow one not only to obtain the expression for molecular resonance energies (RE ) and numerical estimates for RE , but also they provide the basis for discussion of local molecular features, such as ring characterization and Pauling bond orders.     

Enumeration of conjugated circuits in nanotubes

The resonance energy of (1,1)n "armchair" carbon nanotubes and (n,n)1 nanoribbons was determined by enumerating the conjugated circuits (CC) and the Kekulé structures. The lower indices denote the number of hexagon layers. It was found that the resonance energy per carbon atom is equal to 0.160 eV in (1,1)n tubes and 0.142 eV in (n,n)1 tubes.     

Crystal structure of the gold nanoparticle [N(C8H17)4][Au25(SCH2CH2Ph)18

We report the crystal structure of the thiolate gold nanoparticle [TOA+][Au25(SCH2CH2Ph)18-], where TOA+ = N(C8H17)4+. The crystal structure reveals three types of gold atoms: (a) one central gold atom whose coordination number is 12 (12 bonds to gold atoms); (b) 12 gold atoms that form the vertices of an icosahedron around the central atom, whose coordination number is 6 (five bonds to gold atoms and one to a sulfur atom), and (c) 12 gold atoms that are stellated on 12 of the 20 faces of the Au13 icosahedron. The arrangement of the latter gold atoms may be influenced by aurophilic bonding. Together they form six orthogonal semirings, or staples, of -Au2(SCH2CH2Ph)3- in an octahedral arrangement around the Au13 core.     

Bounds for reactivity indices

Lower and upper bounds are derived for bond number, localization energy and atom self-polarizability of alternant hydrocarbons. It is proved that in acyclic polyenes the maximal bond number is 1, 2 and 3, respectively for primary, secondary and tertiary carbon atoms.