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。     

原子电负性的新研究

原子电负性是一应用十分广泛的重要物理量，已有很多表示方法，有关评论文章也很多。Pauling把电负性定为为“原子在分子中吸引电子的能力”。按Pauling电负性定义，键合原子不同，分子中原子吸收电子的能力也不同，因此原子电负性不是恒定值。为了     

密度泛函理论下的分子总体电负性与调和平均电负性的关系

根据密度泛函理论定义的有效原子电负性，讨论了分子中总体电负性与调和平均电负性之间的关系，得到了调和平均电负性非常接近于总体电负性的结论，同时，说明了两者相似的原因，并对一系列分子给出了它们的数值比较．     

原子-键电负性均衡方法中的σπ模型及应用

带有双键或共轭双键的化合物可进行加成、氧化和聚合等反应,在有机、生物和制药等领域用途广泛．密度泛函理论下的电负性均衡方法在研讨分子电荷分布和反应性等方面有独特优势［１～４］．在电负性均衡方法中,Ｍｏｒｔｉｅｒ［１］的电负性均衡方法引人注目,但其未考虑分子中化学键的存在．Ｇｈｏｓｈ［２］的半经验电负性均衡方法考虑了化学键电荷,但键电荷取值假定太简单,只能处理双原子分子．Ｙａｎｇ［３,４］等的原子－键电负性均衡方法同时考虑了分子中原子和化学键的存在,取得令人满意的结果．至今尚无人明确地考虑双键的结构…     

对鲍林电负性物理本质的探讨

鲍林电负性标度应用很广,但长期以来其物理意义不甚明瞭。本文试图通过建立等效氢原子模型,运用原子的价电子电离势的精确实验数据,建立新的电负性标度,从而探讨鲍林电负性的物理意义。在此之前先对鲍林及缪立根（Mulliken）电负性简介如下： 一、鲍林、缪立根电负性概述鲍林电负性的定义是：电负性是元素的原子在分子中吸引电子的能力。     

原子的电负性

原子的电负性在化学中有许多应用.求极性键键长、极性分子分解能以及用分子轨道法求分子轨函等,均应用电负性概念. 至目前止,原子的电负性已有数种度量标尺,其中Mulliken的电离势及电子亲合势平均值度量法的理论根据较好,而Pauling的热化学数据度量法应用较广. 为求得各种原子的电负性,已有多种可供计算的公式.刘遵宪由原子价壳层电子     

ABEEM方法预测响应函数

在密度泛函理论和原子-键电负性均衡模型基础上,定义了与化学键有关的响应函数以及化学键区域的Fukui函数,建立了一套快速确定分子中各区域(包括原子区域和化学键区域)响应函数的新方法.对大量分子的响应函数的计算结果表明,该方法得到的响应函数可以较好地预测分子中各点的反应活性,并更加快捷省时,展示了原子-键电负性均衡模型的广阔应用前景.     

确定大分子体系电荷分布的新方法

近年来，应用密度泛函理论探求电负性和硬度与体系中电荷分布之间的关系，成为令人关注的课题[1~5]．Mortier[1,2]的电负性均衡方法（EEM）没有考虑化学键电荷．Ghosh[4]的半经验电负性均衡方法考虑了化学键电荷，但键电荷取值假设太简单．本文同时考虑了分子中的原子电荷和键电荷的作用，给出了分子中原子和化学键有效电负性的精密公式，这些公式为发展一个系统的精密电负性均衡方法及应用奠定了基础．1理论方法以密度泛函理论[6]为基础，将分子的单电子密度ρmol（r）按式（1）分割：式中ρα（r）是分子中α原子区域的单电子密度，ρα…     

密度泛函理论下的分子电负性——Ⅵ.原子键电负性均衡模型

以密度泛函理论和电负性均衡原理为基础 ,将体系的单电子密度分割为原子的单电子密度和键的单电子密度 ,得到了分子总能量、分子中原子以及键的有效电负性的表达式 .基于这些表达式 ,提出了直接计算体系的总能量和体系中电荷分布的新方法 .此模型比其他电负性均衡方法更合理 .对大量分子的总能量和电荷分布所进行的计算结果表明所提出的原子 键电负性均衡模型是可行的 ,可以应用于确定各类生物和有机大分子的总能量和电荷分布 ,给出较EEM和MEEM模型更近于从头计算的结果     

有机化合物中功能团电负性的估算

在无机化学中,元素的电负性是指元素的原子在分子内吸引电子的能力。这种能力的大小决定该原子在分子内是正性还是负性,以及所形成的化学键的极性。目前虽然还无法直接测定元素的电负性,但其相对值却是比较完整的。在有机化学中,有机化合物的性质往往取决于化合物的功能团,而功能团的相对电负性是影响其性质的一个主要因素。关于有机物功能团的相对电负性这一问题, 不少人曾做了大量的工作,他们用不同的方法对有机物功能团的电负性进行了经验估算,集累了部分数据。     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

CoFe2O4自形成磁性液体场致结构化对磁化的影响

The Langevin paramagnetic theory can’t describe the relation between magnetization of ferrofluids and applied magnetic field. The structuralization of ferrofluids, which is considered the main influence factor of the magnetization, is regarded. The part of magnetization works is deposited when the structure is forming. This action influences the magnetization of ferrofluids directly or indirectly. On the base of the “compressing” model, the Langevin function that usually describes the magnetization of ferrofluid is modified, and a well-fitted curve is obtained. An equation of the relation between the equivalent volume fraction after being “compressed” and the intensity of magnetic field is discovered, which approximately describes the process of magnetization. The relation between the approximate initial susceptibility and the volume fraction can be obtained from modified formula.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.     

Chemistry of heterocyclic compounds at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences, over 50 years (Review)

The review contains a concise historical account and information on the most significant researches undertaken by the staff at the A. E. Favorsky Irkutsk Institute of Chemistry, Siberian Branch of the Russian Academy of Sciences on the Chemistry of Heterocyclic Compounds. Dedicated to Academician of the Russian Academy of Sciences B. A. Trofimov on his 70th jubilee. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1443–1502, October, 2008.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.