用Hirshfeld 电荷定量标度亲电性和亲核性: 含氮体系

准确预测化学过程中分子内各原子提供或接受电子的能力以及化学反应可能的位点, 即定量确定亲电性、亲核性和区域选择性, 是一个十分重要却仍然亟待解决的课题. 此前, 基于我们新近提出的信息守恒原理,曾建议使用Hirshfeld 电荷和信息增益作为两个等价的描述符用于此目的. 我们的这个想法已经被成功地应用于两个系列的分子体系, 且其有效性得到了充分的验证. 然而, 先前我们只考察了碳元素的这些性质, 所以其结论的普遍性仍存在疑问. 我们尚不清楚它是否适用于其他元素, 而且对于同一元素的不同价态该结论是否适用也不清楚. 为此, 本文将考察含氮体系. 对5 个不同类别的含氮体系共计40 个分子进行了研究, 其中包括重氮苯、偶氮、重氮、一级和二级胺体系. 结果表明, 对所有五个含氮体系其Hirshfeld 电荷与实验得到的亲电性和亲核性标度之间仍然存在着较强的线性关联. 然而, 这些相关性却依赖于氮元素的化合价类型和键合环境. 该线性关系只能在同一类型中成立. 我们对其可能的原因进行了讨论.     

芳香化合物亲核、亲电反应活性的理论预测和实验反应速率的相关性研究

选择自然布局分析(NPA)电荷、Hirshfeld电荷、分子范德华表面1.6?处的静电势、最低未占据轨道(LUMO)成分、分子范德华表面1.6?处的平均局部离子化能、简缩福井函数和简缩双描述符来预测芳香族化合物亲核加成、亲核取代和亲电反应的活性位点,并分析理论预测结果和实验反应速率之间的相关性.发现这些方法都能准确地预测反应的活性位点.还发现不管对亲核反应还是对亲电反应,体现局部电子硬度的方法,如Hirshfeld电荷和分子范德华表面1.6?处的静电势,其预测结果的大小能较好地反映实验反应速率的相对大小,而体现局部电子软度的方法,简缩福井函数和简缩双描述符,其预测结果和实验反应速率的相关性较小.     

羰基衍生物亲水性的研究

羰基衍生物的水解反应和水合反应是按亲核加成机理进行的.所以,羰基碳原子的亲电性对反应的难易起决定作用.一、原子电荷判据文献中常以电子电荷较少作为原子亲电性的度量.如苯环上的亲核取代反应就是这样解释的.对羰基衍生物,我们选取了:甲酰胺、甲醛、甲酰氟及乙烯脲、一硝基乙烯脲、二硝基乙烯脲两个模型分子系列进行讨论.它们的亲水性次序分别是:     

预测亲核反应位点方法的比较

预测分子不同位点发生亲核取代反应的活性具有重要的理论和实际意义.目前已提出了许多基于反应物自身电子结构特点的预测方法.本文将碳基化合物、芳香族化合物和吡啶衍生物这3类分子作为测试体系,对14种预测方法的可靠性进行了详细的比较分析.结果表明,体现局部电子软度的方法能很好地预测反应位点,如简缩双描述符方法,但表现静电效应的预测方法,如原子电荷分析和静电势分析,整体表现很差.对于本文中所用的分子体系来讲,简缩双描述符和Hirshfeld电荷分析方法对分子反应位点预测最准确.     

亲核试剂在正离子聚合反应中的作用及其作用机理的研究

研究了亲核试剂对IB 1 ,3 二 (2 氯异丙基 )苯 (DiCumCl) TiCl4体系正离子聚合反应的规律 ,亲核试剂与增长的碳正离子作用的紫外光谱图 ;采用分子模拟 ,利用量子力学半经验方法计算了亲核试剂与质子反应的活化能 ,确定了不同亲核试剂与质子的作用能力 ;利用分子力学方法计算了在增长碳正离子末端的不同位置亲核试剂与之络合的稳定化能 ,根据能量最低原则确定了亲核试剂在碳正离子链端的作用位置 ;利用分子力学方法进行构象优化后 ,借助QEq方法得到了聚异丁烯碳正离子和聚苯乙烯碳正离子的电荷数值 .综合以上实验结果提出了亲核试剂在正离子聚合反应中的作用及其作用机理     

重氮苯与不同亲核试剂结合选择性:共价与非共价作用分析

重氮苯与亲核试剂的作用方式及其反应机理一直未能被完全阐明. 基于密度泛函理论, 本文计算了 6种亲核试剂与重氮苯结合时的结合位点及反应过程中的反应坐标. 计算结果表明, 化学硬度可以作为预测不同亲核试剂与重氮苯结合位点的主要描述符. 基于复合物体系范德华表面的平均局域离子化能等参数, 还提出了可以定量预测重氮苯与亲核试剂结合反应活化能垒的描述符. 这些理论研究结果对理解重氮苯与亲核试剂的反应机制、 寻找更优反应条件具有重要意义.     

有机锗亲核试剂的交叉偶联反应

在过渡金属催化的交叉偶联反应中,有机硅、锡化合物作为偶联亲核试剂已经广为人知,然而同族的锗元素研究却相对较少。锗亲核试剂的偶联反应最初只是简单地证明了锗作为一种"偶联元素"的可行性,但逐步发现的优异性质使得锗试剂已经受到越来越多的关注。本文从锗试剂的结构分类出发,介绍这些锗片段引入有机体系的方法及相应锗试剂的交叉偶联反应。     

α-重氮膦酸酯作为亲核试剂参与不对称反应的研究进展

重氮化合物作为一类重要的合成子,在有机合成、药物化学、材料化学及化学生物学等领域均有广泛应用。α-重氮膦酸酯作为α-重氮羧酸酯的电子等排物,可作为亲核试剂参与不对称反应。综述了α-重氮膦酸酯作为亲核试剂参与不对称反应（Mannich反应,Morita Baylis-Hillman反应,类Aldol反应以及［3+2］反应）的研究进展,并对其未来发展进行了展望。     

掌握反应物电性结构轻松记忆有机反应

有机反应按成键方式可以分为自由基反应、离子型反应和协同反应,基础有机化学中涉及的大部分反应属于离子型反应。掌握反应物的电性结构,清楚反应物中的亲核部位和亲电部位,不仅有助于学生理解离子型反应历程,轻松记忆反应,而且有助于学生举一反三,触类旁通,推导出课本中未曾讲述的反应。     

氟烷基化和氟烷氧基化的研究18.2-卤四氟碘乙烷与含氮亲核试剂的反应

2-卤四氟碘乙烷[1,XCF_2CF_2I,(X=Cl或l)]能与多种亲核试剂按自由基或亲卤机理反应。1在没有溶剂时,于室温下,可以和胺作用迅速形成分子络合物。本文则进一步报道1与含氮亲核试剂在各种溶剂中反应的结果。     

Valence state parameters of all transition metal atoms in metalloproteins—development of ABEEMσπ fluctuating charge force field

To promote accuracy of the atom‐bond electronegativity equalization method (ABEEMσπ) fluctuating charge polarizable force fields, and extend it to include all transition metal atoms, a new parameter, the reference charge is set up in the expression of the total energy potential function. We select over 700 model molecules most of which model metalloprotein molecules that come from Protein Data Bank. We set reference charges for different apparent valence states of transition metals and calibrate the parameters of reference charges, valence state electronegativities, and valence state hardnesses for ABEEMσπ through linear regression and least square method. These parameters can be used to calculate charge distributions of metalloproteins containing transition metal atoms (Sc‐Zn, Y‐Cd, and Lu‐Hg). Compared the results of ABEEMσπ charge distributions with those obtained by ab initio method, the quite good linear correlations of the two kinds of charge distributions are shown. The reason why the STO‐3G basis set in Mulliken population analysis for the parameter calibration is specially explained in detail. Furthermore, ABEEMσπ method can also quickly and quite accurately calculate dipole moments of molecules. Molecular dynamics optimizations of five metalloproteins as the examples show that their structures obtained by ABEEMσπ fluctuating charge polarizable force field are very close to the structures optimized by the ab initio MP2/6–311G method. This means that the ABEEMσπ/MM can now be applied to molecular dynamics simulations of systems that contain metalloproteins with good accuracy. © 2014 Wiley Periodicals, Inc.     

The nucleophilicity N index in organic chemistry

The nucleophilicity N index (J. Org. Chem. 2008, 73, 4615), the inverse of the electrophilicity, 1/ω, and the recently proposed inverse of the electrodonating power, 1/ω?, (J. Org. Chem. 2010, 75, 4957) have been checked toward (i) a series of single 5-substituted indoles for which rate constants are available, (ii) a series of para-substituted phenols, and for (iii) a series of 2,5-disubstituted bicyclic[2.2.1]hepta-2,5-dienes which display concurrently electrophilic and nucleophilic behaviors. While all considered indices account well for the nucleophilic behavior of organic molecules having a single substitution, the nucleophilicity N index works better for more complex molecules. Unlike, the inverse of the electrophilicity, 1/ω, (R(2) = 0.71), and the inverse of the electrodonating power, 1/ω? (R(2) = 0.83), a very good correlation of the nucleophilicity N index of twelve 2-substituted-6-methoxy-bicyclic[2.2.1]hepta-2,5-dienes versus the activation energy associated with the nucleophilic attack on 1,1-dicyanoethylene is found (R(2) = 0.99). This comparative study allows to assert that the nucleophilicity N index is a measure of the nucleophilicity of complex organic molecules displaying concurrently electrophilic and nucleophilic behaviors.     

Role of reversible dimerization in reactions of amphoteric aziridine aldehydes

Unprotected aziridine aldehydes belong to the amphoteric class of molecules by virtue of their dual nucleophilicity/electrophilicity. The dimeric nature of these molecules, brought together by a weak and reversible aminal "connection", was found to be an important element of reactivity control. We present evidence that reversible dimer dissociation is instrumental in aziridine aldehyde transformations. We anticipate further developments that will unveil other synthetic consequences of remote control of selectivity through forging reversible covalent interactions.     

Synthesis of poly(2‐oxazoline)s with side chain methyl ester functionalities: Detailed understanding of living copolymerization behavior of methyl ester containing monomers with 2‐alkyl‐2‐oxazolines

Poly(2‐oxazoline)s with methyl ester functionalized side chains are interesting as they can undergo a direct amidation reaction or can be hydrolyzed to the carboxylic acid, making them versatile functional polymers for conjugation. In this work, detailed studies on the homo‐ and copolymerization kinetics of two methyl ester functionalized 2‐oxazoline monomers with 2‐methyl‐2‐oxazoline, 2‐ethyl‐2‐oxazoline, and 2‐n‐propyl‐2‐oxazoline are reported. The homopolymerization of the methyl ester functionalized monomers is found to be faster compared to the alkyl monomers, while copolymerization unexpectedly reveals that the methyl ester containing monomers significantly accelerate the polymerization. A computational study confirms that methyl ester groups increase the electrophilicity of the living chain end, even if they are not directly attached to the terminal residue. Moreover, the electrophilicity of the living chain end is found to be more important than the nucleophilicity of the monomer in determining the rate of propagation. However, the monomer nucleophilicity can be correlated with the different rates of incorporation when two monomers compete for the same chain end, that is, in copolymerizations. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2649–2661     

Electrophilicity and nucleophilicity index for radicals

Radicals can be regarded as electrophilic/nucleophilic, depending on their tendency to attack sites of relatively higher/lower electron density. In this paper, an electrophilicity scale, global as well as local, and a nucleophilicity scale for 35 radicals is reported. The global electrophilicity scale correlates well with the nucleophilicity scale, suggesting that these concepts are inversely related.