分子中芳香性自动识别算法

以图论为基础,从化合物的二维连接表出发,在环识别算法的约束下,对分子中的节点进行判断。结果表明,该算法能够识别大多数化合物中的芳香性。作为约束条件,把芳香性的识别算法应用于ESESOC系统中结构的穷举生成,得到了较好的结果。     

一种计算桥环化合物环数的简便方法

陈亚元同志在“桥环化合物环数的计算方法”一文中,提出了几种如何计算比较复杂的桥环化合物环数的具体方法,同时还介绍了P.A.Reddy对桥环化合物中环数的计算公式c=b-a+1(c为环数,b为环上的键总数,a为环上的原子总数),从而为计算桥环化合物的环数提供了比较简便的方法。由于桥环化合物与桥头原子并存,而化合物中桥头原子的总数目(包括主桥头原子和次桥头原子)又与环数的多少密切相关,所以,可以用桥环化合物中桥头原子的总数来正确计算桥环化合物的环数。设一种桥环化合物中的桥头原子总数为N,环数为M,根据两个桥头原子可以构成一个双环的原则,推导出计算环数的一般公式:     

中环萜类化合物的合成

本文综述了中环萜类化合物的各种合成方法, 它们根据成环方式可以分为四类: 1. 双环或三环化合物的桥键断裂, 2.无环化合物的环合, 3.常规环化合物的环扩大, 4. 大环化合物的环缩小.     

有机纳米环/格的研究进展

径向共轭的碳纳米环作为碳纳米管的纳米片段,在合成化学、立体化学、超分子化学和材料科学领域引起了极大的关注.从几何结构角度来看,纳米环的结构分为单环纳米环和多环纳米环.其中,单环纳米环的构建模块主要有苯或多环芳烃以及大环,与以苯或多环芳烃为模块构造的单环纳米环相比,以大环为构建模块的单环纳米环和多环纳米环不仅具有特殊的拓扑结构还具有较高的荧光量子产率、较大的空腔等特点.目前这类具有拓扑结构的纳米环分子在主客体掺杂、储能材料、多孔和有机光电材料等领域体现出重要的研究价值.因此本综述将重点对卟啉类单环纳米环、“8”字型纳米环、纳米格以及更复杂的碳纳米笼的合成方法进行全面的综述.     

非糖类化合物合成碳环糖*

碳环糖是一类呋喃或吡喃糖环中的氧原子被亚甲基取代后形成的糖类似物。碳环糖作为糖类化合物的类似物,和糖类化合物有着不同的活性和稳定性,已经引起了人们的广泛关注。本文综述了从非糖类化合物合成五元及六元碳环糖研究的最新进展。重点介绍了以环二烯基硅烷、奎宁酸、降冰片烯等碳环化合物为原料合成碳环糖的进展。     

一价铑催化的1-取代乙烯基环丙烷的形式上[5+1]/[2+2+1]环加成反应:一步构建多官能团化的5/5/6三环化合物

自然界中高生物活性的天然产物一般都以多环化合物作为它的骨架或者骨架组成单元.因此,对于现代有机合成化学来说,要高效地合成这些天然产物和其类似物来开发新药物分子,就有必要发展高效的、普适性广的合成方法来构建多环化合物.北京大学化学与分子工程学院余志祥课题组利用一价铑催化的1-取代乙烯基环丙烷化合物与     

环钯化合物合成及其在催化中的应用

环钯化合物由于丰富的结构、高度的稳定性和卓越的催化性能,已成为钯化学研究的热点之一。迄今已开发出了C-H键活化、氧化加成、转金属化、亲核加成和配体交换等多种方法,可制备出从三元环到十一元环的CY型环钯化合物和多种YCY型环钯化合物。环钯化合物目前已应用于偶联、烯烃氢化和不对称催化等反应中。本文简单介绍了环钯化合物的种类,重点介绍了环钯化合物的合成方法和催化应用情况,最后提出了环钯化合物在今后合成研究和催化应用中的发展建议。     

一种通过剪断最短桥确定复杂桥环化合物主环的方法介绍

确定主环是命名复杂桥环化合物的难点所在。我们介绍一种"剪断最短桥,显露最大环"的方法,可以帮助学生快速准确地确定最大环的位置,从而对复杂桥环化合物命名。     

氧杂环丁烷的扩环反应

氧杂环丁烷是一类重要的小杂环化合物,也是重要有机合成中间体,在有机化学、药物化学和高分子化学中都有广泛的应用.作为具有较大环张力的小杂环化合物,氧杂环丁烷类化合物除可以发生开环反应外,也很容易发生扩环反应,构建含氧普通环到大环化合物.主要总结了氧杂环丁烷的扩环反应,包括重氮化合物作为卡宾前体与氧杂环丁烷的扩环反应、金属催化的分子间环加成和邻基参与的分子内环加成反应及亲核扩环反应等.分析了一些扩环反应的机理,并对扩环反应未来的发展提出了新的展望.     

α-重氮-1,3-环己二酮类化合物在有机合成中的应用

金属铑盐催化下α重氮环二酮与π键的［３＋２］环加成反应是合成复杂的稠杂环化合物的一种简捷有效的新方法，本文重点介绍了α重氮１３环己二酮通过这类反应合成呋喃环结构化合物的最新研究成果。     

关于空间群判断失误的札记I.最小素单胞的选取

导出反映晶体结构周期的最小素单胞是正确判断空间群的第一步,其中以还原单胞的选择最为理想。它不仅具有选择的唯一性,且便于确定布拉维格子的类型。本文还讨论单胞选取过小和过大的实例,并给出正确的单胞和空间群以及原子坐标。     

Relation between Polymer Conformational Structure and Dynamics in Linear and Ring Polyethylene Blends

Atomistic molecular dynamics simulations of ring‐linear polyethylene blends are employed to understand the relationship between chain conformational structure and the melt dynamics of these blends. As observed in previous studies, this study confirms that ring polymers in pure melts do not exhibit screened excluded volume interactions, contrary to linear polymers. Moreover, the average molecular shapes of the rings are quite distinct from both swollen and ideal ring polymers under theta conditions, and instead rather resemble branched polymers with screened binary excluded volume interactions, e.g., percolation clusters. Upon adding linear chains to a melt of pure rings, we find significant swelling of the rings and a corresponding shape change that is qualitatively similar to dissolving rings in a small molecule good solvent. This swelling, arising from altered self‐excluded volume interactions, translates into a large decrease in ring diffusivity, an effect that becomes more amplified when the polymer melt is entangled.     

Enantiomerically enriched cyclopropene derivatives: versatile building blocks in asymmetric synthesis

Enantiomerically enriched cyclopropene derivatives, the smallest possible unsaturated carbocycles, are of great synthetic interest since they serve as versatile reactive building blocks. Their reactivity results from the relief of the ring strain in the small molecule. They can be transformed into a wide variety of complex chiral structures and a special emphasis will be directed towards the preparation of enantiomerically enriched methylene- and alkylidenecyclopropane derivatives. The ready availability of a wide range of these chiral entities now provides an excellent opportunity to discover new and unique transformations that can further enrich mainstream synthetic methodology.     

Modification of proline‐based 2,5‐diketopiperazines by anionic ring‐opening polymerization

2,5‐Diketopiperazines (DKPs) are the smallest cyclic dipeptides found in nature with various attractive properties. In this study, we have demonstrated the successful modification of proline‐based DKPs using anionic ring‐opening polymerization (AROP) as a direct approach. Four different proline‐based DKPs with various side chains and increasing steric hindrance were used as initiating species for the polymerization of 1,2‐epoxybutane or ethoxyethyl glycidyl ether in the presence of t‐BuP₄ phosphazene base. The addition of a Lewis acid, tri‐isobutyl aluminum, to the reaction mixture strongly decreased the occurrence of side reactions. Impact of the DKP side‐chain functionalities on molar mass control and dispersity was successfully evidenced. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1008–1016     

A Core‐Expanded Subphthalocyanine Analogue with a Significantly Distorted Conjugated Surface and Unprecedented Properties

The introduction of a seven‐membered‐ring unit in the place of a five‐membered‐ring unit in the structure of subphthalocyanine resulted in significant distortion of the bowl‐shaped structure of the conjugated molecule as well as the following unprecedented properties: the preferential formation of the axially fluoro substituted species, the fluttering‐dynamic‐motion‐induced rapid exchange of P and M enantiomers, markedly split Q‐band absorption, and a clear difference in the ring‐current effects arising from the convex and concave surfaces.     

Molecular design of tautomeric interconversions of heterocycles

A classification and methodology of molecular design of ring—chain—ring (ring—ring) tautomeric systems by superposition of ring—chain equilibria in a structure of one molecule are considered.     

Structures and bonding of B4O5 and B4O5− clusters: Emergence of boroxol ring and competition between rhombic B2O2 and hexagonal B3O3 cores

Boron oxide clusters are electron-deficient species with novel structures and bonding, in which the emergence of rhombic and boroxol rings is of interest. We report on computational prediction of the global-minimum structures for two boron oxide clusters: B₄O₅ and B₄O₅⁻. These structures differ distinctly, as established through global machine searches and electronic structure calculations at B3LYP and single-point CCSD(T) levels. While B₄O₅ neutral cluster has a rhombic B₂O₂ core, the B₄O₅⁻ anion features a boroxol B₃O₃ ring. One electron completely changes the potential landscapes. Bonding analyses show that the 4π electron-counting is crucial for a rhombic B O cluster, in contrast to π sextet for a boroxol ring, which underlies the competition between rhombic and boroxol rings in B₄O₅/B₄O₅⁻ clusters. A possible pathway for rhombic-to-hexagonal transformation is proposed based on intrinsic reaction coordinate calculations. Anion B₄O₅⁻ cluster, a new member of the inorganic benzene family, is among the smallest B O species with a free-standing boroxol ring, governed collectively by composition and electron-counting.     

Quantum delocalization of benzene in the ring puckering coordinates

The effect of quantum mechanical delocalization of atomic nuclei on the conformation of the six‐membered ring structure in two hydrocarbons, cyclohexane and benzene, is investigated using ab initio path integral approach. A striking feature of benzene species is revealed using ring puckering coordinate representation, which demonstrates that the zero point motion of the heavy atom skeleton dominates over the out‐of‐plane thermal motions of the ring. Even more unexpected is the fact, that this is true not only at low temperature of 150 K, at which such behavior would not be surprising, but also at room temperature, where the nuclear quantum effects are usually of lesser importance, especially in the case of such heavy nuclei as carbon. In view of this finding the planar conformation of benzene, whose equilibrium (T = 0 K) geometry results from the well‐known properties of the electronic structure, can be elucidated also at nonzero temperature. According to our simulations, it appears as a consequence of quantum delocalization of the carbon nuclei rather than a trivial time average over the classical configurations of the puckered ring. This interesting behavior is contrasted with the clearly nonplanar structure of cyclohexane, whose ring puckering states can be unequivocally assigned even if the nuclear delocalization is taken into account. © 2014 Wiley Periodicals, Inc.     

Controlling coffee ring structure on hydrophobic polymer surface by manipulating wettability with O2 plasma

A simple and novel method is firstly reported for controlling coffee ring structure on polystyrene (PS) film surface by O₂ plasma. O₂ plasma treatment leads to the wettability change of PS surface from hydrophobic to hydrophilic. For hydrophilic PS surface the coffee ring structure is avoided relying on the motion of contact line (CL) while SiO₂ microspheres are left. The motion of the CL is produced based on the viscosity and Marangoni effect with the addition of polymer additives. For hydrophobic PS surface coffee ring structure still persists even with polymer additives because SiO₂ microspheres transfer with the motion of the CL at the beginning of droplet evaporation and accumulate at the droplet edge at late stage with the pinning of the CL. As a result, uniform and macroscale SiO₂ microspheres deposition without coffee ring structure and SiO₂ microspheres deposition with coffee ring structure are controlled by O₂ plasma. This method provides a new way to tune coffee ring structure with smart surface and may be potentially useful for a range of application at material deposition and diagnosing diseases.