Cl原子与CH2SH自由基反应机理及电子密度拓扑研究

采用MP2(Full)/6-311G(d,p)和B3LYP/6-311G(d,p)找到了反应Cl＋CH₂SH→HCl＋CH₂S的两个可能的反应通道, 得到了各反应通道的反应物、中间体、过渡态和产物的优化构型、谐振频率. 对反应进程中若干关键点进行了电子密度拓扑分析, 讨论了反应进程中键的断裂、生成和化学键的变化规律, 找到了该反应的结构过渡区(结构过渡态)和能量过渡态, 发现了反应热与结构过渡区之间的关系.     

Nuclear spin relaxation in poly(diethylsiloxane)

Earlier work showed that heating causes poly(diethylsiloxane) to undergo a first-order transition from a semicrystalline solid to a more mobile viscous—crystalline material. The latter is composed of two phases and analogies between polymer and liquid crystal morphology and behavior have been made. The viscous—crystalline phase in PDES appears to be unique since the literature is devoid of other documented examples. In this study, spin—lattice and spin—spin relaxation times were measured over a wide temperature range. They show a glass transition at 138°K, a crystal—crystal transition at 206°K, and a transition around 250°K which results from translational motion of the polymer chains with respect to each other. This motion is observed in the amorphous phase at a lower temperature than in the crystalline phase. Translational motion in the crystalline phase is observed on melting of the crystallites. The spin—spin data permitted monitoring of the molecular motions in each phase and the data suggest that these phases exert some influence on the molecular motions of each other. The viscous—crystalline phase in PDES may represent a unique model for studying and understanding “precrystalline” behavior and structure in amorphous solids.     

Aromaticity and Pericyclic Reactions

Pericyclic reactions formally resemble the conversion of one Kekulé structure into another; the transition state may be “aromatic”, “nonaromatic”, or “antiaromatic”. Thermally induced pericyclic reactions proceed preferentially via aromatic transition states whereas their photochemical counterparts lead to products that are formed via antiaromatic transition states.     

The hierarchic order in the solid state,part IV States of “optimal hierarchic order” solid—“Meltlike” transitions

An attempt is made to gain an understanding for “unusual” properties of extremely thin films and extremely small grains. Lamelles of gold are known to flow together far below the melting point. Independent from temperature a certain load is found, under which a film of given thickness undergoes neither elongation nor contraction. At a certain distribution of building units over the various hierarchic levels—as roughly corresponding to a characteristic ratio of surface to volume—the system is found in a state of optimal hierarchic order (OHO). In passing this state (due to an increase in surface to volume ratio) the system appears to undergo transition into a “meltlike” state. It is proposed that the slope of the curve at the point of inflexion (and intersection) in the plot of load vs. rate of expansion or contraction may serve as a measure of the hierarchic order of the system under consideration. The question is raised in what ways observable changes in structure sensitive properties, such as strength or conductivity, may be related to changes in hierarchic order.     

Structural fluctuation and atom-permutation in transition-metal clusters

The atomic structure and thermodynamic properties of transition-metal clusters containingN atoms are investigated forN=6 and 7 using the method of molecular dynamics, where Gupta's potential taking into account many-body interaction is employed. The caloric curve (total energy — temperature curve) and the structural fluctuations are studied. The “fluctuating state” is found forN=6 in the region of the temperature near below the melting point, where clusters undergo structural transition from one isomer to others without making any topological change. The fluctuating state differs from the coexistence state in that the former involves no atomic diffusion, and goes to a structural phase transition of the bulk whenN is increased. On the other hand, the motion of atom-permutation is found in the low-temperature region of the liquid state, being induced by the cooperative motion of two atoms. It is discussed that such a motion easily occurs along the surface and may be considered to be one of the characteristics of small clusters. The fluctuating state is discussed in relation to the structural fluctuation of gold clusters observed experimentally.     

Calculating the number of spanning trees in a labeled planar molecular graph whose inner dual is a tree

The quantum mechanical relevance of the concept of a spanning tree extant within a given molecular graph—specifically, one that may be considered to represent the carbon-atom connectivity of a particular (planar) conjugated system—was first explicitly pointed out by Professor Roy McWeeny in his now-classic 1958 memoire entitled “Ring Currents and Proton Magnetic Resonance in Aromatic Molecules.” In a recent work, Gutman and one of the present authors proposed a scheme for calculating the number of spanning trees in the graph associated with catacondensed, benzenoid molecules which, by definition, contain rings of just the one size (six-membered); here, we present an algorithmic approach that enables the determination of the number of spanning trees in the molecular graph of any catacondensed system (which, in general, has rings of more than one size, and these may be of any size). An illustrative example is given, in which the algorithm devised is applied to a (hypothetical) pentacyclic catacondensed structure comprising a five-membered ring, a six-membered ring, a seven-membered ring, and two four-membered rings. © 1996 John Wiley & Sons, Inc.     

Liquid Metals and Liquid Semiconductors

Numerous liquid systems have electrical properties which resemble those of crystalline and amorphous semiconductors. The existence of “semiconducting” behavior in these liquids is mostly related to a continuous transition from a metallic to a “semiconducting” state when a thermodynamic variable such as temperature, density or concentration is changed. Changes in the nature of the chemical interaction and the associated changes in the structure of the liquid are of fundamental importance for the transition to a “semiconducting” state. This will be demonstrated for the ionic liquid CsAu, for covalent liquid selenium, and for expanded liquid metals.     

CH2ClO与NO反应机理的理论研究

采用B3LYP, MP2方法在6-31＋(d,p)和6-311＋＋G(d,p)水平研究了CH₂ClO自由基与NO反应的微观机理, 找到了三个可能的反应通道. 并得到了各反应通道的反应物、中间体、过渡态和产物的优化构型、谐振频率. 成功地解释了Wu等的实验结论. 从电子密度拓扑分析的角度, 讨论了化学反应过程中化学键的变化规律, 为实验研究大气化学反应提供理论依据. 找到了该反应的结构过渡态(结构过渡区)和能量过渡态, 发现了反应热与结构过渡区之间的关系.     

Reaction force analyses of nitro-aci tautomerizations of trinitromethane, the elusive trinitromethanol, picric acid and 2,4-dinitro-1H-imidazole

We have analyzed computationally, in terms of the reaction force, the nitro → aci tautomerizations of trinitromethane, trinitromethanol, picric acid and 2,4-dinitro-1H-imidazole. These processes involve intramolecular transfer of a hydrogen to an NO₂ oxygen, forming the aci tautomer (a nitronic acid). The reaction force naturally and unambiguously divides an activation barrier into two components: (1) the energy required for initial structural changes in the reactant(s), and (2) the energy associated with the first portion of the transition to product(s). In each of these tautomerizations, the first component is dominant. For trinitromethane, it is so large that the resulting total activation barrier makes C–NO₂ bond scission energetically preferable. On the other hand, trinitromethanol—which appears to be unknown—readily undergoes fragmentation in conjunction with hydrogen transfer. Picric acid has the interesting feature that the reaction is almost complete after the first portion of the activation process, marked by the minimum of the reaction force. In all four reactions, the properties of the systems at the force minimum, transition state and force maximum are consistent with the concept of a “transition” region in a chemical reaction versus simply a transition state.     

Gradient‐driven molecule construction: An inverse approach applied to the design of small‐molecule fixating catalysts

Rational design of molecules and materials usually requires extensive screening of molecular structures for the desired property. The inverse approach to deduce a structure for a predefined property would be highly desirable, but is, unfortunately, not well defined. However, feasible strategies for such an inverse design process may be successfully developed for specific purposes. We discuss options for calculating “jacket” potentials that fulfill a predefined target requirement—a concept that we recently introduced (Weymuth and Reiher, MRS Proceedings 2013, 1524, DOI:10.1557/opl.2012.1764). We consider the case of small‐molecule activating transition metal catalysts. As a target requirement we choose the vanishing geometry gradients on all atoms of a subsystem consisting of a metal center binding the small molecule to be activated. The jacket potential can be represented within a full quantum model or by a sequence of approximations of which a field of electrostatic point charges is the simplest. In a second step, the jacket potential needs to be replaced by a chemically viable chelate‐ligand structure for which the geometry gradients on all of its atoms are also required to vanish. To analyze the feasibility of this approach, we dissect a known dinitrogen‐fixating catalyst to study possible design strategies that must eventually produce the known catalyst. © 2014 Wiley Periodicals, Inc.     

A correlation of excited state rotational constants for diatomic molecules

The concepts of “orbital stress” and “transition stress” are defined and applied to N₂, N⁺₂, CO, and CO⁺. The bond lengths and rotational constants of excited electronic states are related to the transition stress, and the response of the electrons and nuclei to the transition stress is shown to be a molecular property, essentially independent of the electronic configuration or state.     

The relative sign of through-bond and through-space interactions; “sigma assistance” of cyclization and intramolecular hydrogen transfer

A perturbational frontier MO model indicates that the relative sign of the through-bond and through-space interaction in nonconjugated bifunctional molecules alternates with the number (N) of intervening sigma bonds. The qualitative predictions from the FMO model are in full accord with quantitative computational and experimental literature data, the latter being mainly available for N<4. It is suggested that alternation of the relative sign of through-bond and through-space interactions with N effect—for which the name “sigma assistance” is proposed—may account for the preference of radical cyclizations to yield odd membered instead of even membered rings and for the preference of hydrogen transfer to occur via an even membered transition state.     

Folded chain crystallization of random terpolymer liquid crystal polymers from the nematic state

The morphology of ca. equimolar random terpolymer liquid crystal polymers of an aliphatic segment of 4–7 carbon atoms, oxybenzoate, and dioxyphenyl crystallized from the nematic state in the form of thin films on glycerine by slow cooling and quenching has been characterized by electron microscopy (TEM) and diffraction (ED). In all cases a folded chain, lamellar structure is found. The ED studies suggest adjacent reentry, and despite a large ΔH, indicate no change in lateral molecular packing at the crystal-“liquid crystal” transition with a transformation to the nematic state at a higher temperature “liquid crystal”-liquid crystal transition. The results are interpreted as suggesting similar folded chain, lamellar morphology in the nematic state. © 1992 John Wiley & Sons, Inc.     

[Fe(H2O)5(NO)]2+, the “Brown‐Ring” Chromophore

Although the “brown‐ring” ion, [Fe(H₂O)₅(NO)]²⁺ ( 1 ), has been a research target for more than a century, this poorly stable species had never been isolated. We now report on the synthesis of crystals of a salt of 1 which allowed us to tackle the unique bonding situation on an experimental basis. As a result of the bonding analysis, two stretched, spin‐polarised π‐interactions provide the Fe–NO binding—and challenge the concept of “oxidation state”.     

Kinetics and mechanisms of diels-alder addition of tetracyanoethylene to anthracene derivatives—II : Solvent effects

The effect of change of solvent on the rate of Diels-Alder addition of tetracyanoethylene (TCNE) to anthracene has been investigated using solvents CCl₄, CHCl₃ and CH₂Cl₂. Solvent effects were measured on the intermediate complex and on the starting materials from solubility measurements. From this, solvent effects on the transition state alone can be evaluated. These effects were remarkable similar to those measured for both the initial state and the intermediate complex suggesting an “early” transition state having a structure similar to that of the intermediate. From the correlation of ΔG_t^≠ (the free energy of transfer from CCl₄ to another solvent for the transition state alone) with the solubility parameter δ², the molar volume of the transition state can be estimated. The result again suggests that the transition state is more “factor” than product-like.     

单烯烃分子结构有限元方法及定量结构-沸点相关性研究

按照有限元方法, 将烯烃分子中的“C—C”单键和“C＝C”双键当作两种不同的线性杆元处理, 构建单烯烃分子的刚度矩阵, 连同质量矩阵求解相应的特征方程, 得到单烯烃分子的结构特征参量——固有频率, 将其用于定量结构-沸点预测模型, 对150个单烯烃分子的沸点实验测定值进行多元回归分析, 结果表明, 单烯烃分子结构与沸点性质间存在高相关性, 说明该方法是合理可行的.     

The appearance of fine structure in the phosphorescence spectra of organic molecules in solid solutions under T1 ← S0 laser excitation

Phosphorescence spectra of coronene. 1,2-benzypyrene and chrysene in bromobutyl at 4.2 K under laser excitation directly in the region of the T₁ ← S₀ transition have been studied. Under these conditions, the phosphorescence spectra acquire a line structure. Vibrational analysis of the spectra has been performed and the frequencies of the normal vibrations of the investigated molecules in the S₀ state have been determined. A “multiplet” structure of the phosphorescence spectra appearing for monochromatic excitation to vibrational sublevels of the T₁ state has been studied. It is shown that the frequencies of the molecular vibrations in a triplet state can be found from an analysis of this structure.     

CH2XH→CH3X (X＝O, S, Se)异构化的量子拓扑研究

利用从头算和量子拓扑方法讨论了CH₂XH→CH₃X (X＝O, S, Se)异构化过程的反应机理. 着重从电子密度拓扑分析计算了反应进程中的各点, 讨论了反应进程中键的断裂和生成, 上述反应都经历了三元环过渡结构, 找到了这类反应的"能量过渡态"和"结构过渡态", 且结构过渡态均在能量过渡态之后出现. 三元结构过渡态结构出现的范围与反应热成正比.