酰胺-盐溶剂体系中的缔合解离平衡和溶剂化效应

本文研究了酰胺-盐溶剂体系中盐的缔合解离平衡和离子的溶剂化效应,以及这些因素对该溶剂体系溶解能力的影响。研究结果表明,盐在溶剂体系中存在多级缔合-解离平衡,阳离子周围有较强的溶剂化效应。自由离子浓度最大和溶剂化效应最强时的盐浓度对应于聚合时的最佳盐用量。     

ZnTBPPc光物理化学性质的溶剂化效应

The solvent viscosity dependence of the photophysical and photochemical properties of tetra(tert-butylphenoxy)phthalocyaninato zinc(II) (ZnTBPPc) is presented. The fluorescence quantum yields (ΦF) and Stern-Volmer′s constant (KSV) for ZnTBPPc fluorescence quenching by benzoquinone in all the solutions followed a semi-empirical law that depends only on the solvent viscosity. ΦF values vary between 0.08 in tetrahydrofuran (THF) and 0.14 in dimethylsulphoxide (DMSO). Triplet quantum yields (ΦT) and lifetimes (...     

DMP与DEP在凝聚相中裂解反应理论研究: 隧道效应与溶剂效应

采用密度泛函理论(DFT)B3LYP方法, 以极化连续模型(PCM)和导体反应场模型(COSMORS)的溶剂模型为基础, 结合反应动力学研究了2,2-二甲氧基丙烷(DMP)与2,2-二乙氧基丙烷(DEP)在凝聚相(溶液相)中的裂解反应. 结果表明, 四元环过渡态裂解反应机理是DMP与DEP裂解反应的主反应通道, 溶剂效应和隧道效应对液相中的裂解反应速率有较大的影响, 而且溶剂效应的影响更显著. 在凝聚相反应理论研究中, 溶剂效应和量子隧道效应都是不能忽略的因素.     

DMP与DEP在凝聚相中裂解反应理论研究∶隧道效应与溶剂效应(英文)

采用密度泛函理论(DFT)B3LYP方法,以极化连续模型(PCM)和导体反应场模型(COSMORS)的溶剂模型为基础,结合反应动力学研究了2,2-二甲氧基丙烷(DMP)与2,2-二乙氧基丙烷(DEP)在凝聚相(溶液相)中的裂解反应.结果表明,四元环过渡态裂解反应机理是DMP与DEP裂解反应的主反应通道,溶剂效应和隧道效应对液相中的裂解反应速率有较大的影响,而且溶剂效应的影响更显著.在凝聚相反应理论研究中,溶剂效应和量子隧道效应都是不能忽略的因素.     

溶剂效应的TLSER描述及其在几类异构化反应中的应用

建立了适合于描述党溶剂效应的理论线性溶剂化能相关(TLSER)模型。并用该模型对四类异构化反应在不同溶剂下的反应自由能或活化自由能与溶剂的分子结构之间的关系进行了研究,确证了模型的合理性。     

钌多吡啶配合物的合成及插入配体的位阻效应对键合DNA的 …

合成了２,５－二甲基－１,４,８,９－四氮三联苯和２,３－二苯基－１,４,８,９－四氮三联苯两种新配体及它们与２,２’－联吡啶和钌的混配物「Ｒｕ（ｂｐｙ）２ｄｍｔａｔｐ」＾２＋（１）和「Ｒｕ（ｂｐｙ）２ｄｐｔａｔｐ」＾２＋（２）,用电子吸收光谱,稳态荧光,粘度测定和圆二色谱研究了配合物与小牛胸腺ＤＮＡ的相互作用。     

红外光谱中溶剂效应机理研究(Ⅳ) 溶剂受电子位阻效应常数的确定

一百多年来，人们对有机化学中的溶剂效应进行了大量研究，提出了种种理论、相应的经验方程和溶剂效应参数．这些经验方程虽然可以在一定范围内较好地处理一些问题，但都不具有普遍性[1，2]作者曾在文献[3，4]中提出碰撞配位理论，并在文献[5]中引入空间位阻效应，提出如下方程，为一系列溶剂确定了供电子效应常数风和供电子位阻效应常数：式中Ei是底物的某具有能量性质的理化性质在溶剂i中的量值（例如反应的平衡常数或速率常数的对数、光谱的波数或频率、化学位移），E0是在正乙烷中的最值；Ai和VAi分别为溶剂i的受电子效应常数和受电子…     

红外光谱中溶剂效应机理研究(IV) 溶剂受电子位阻效应常数的确定

In the previous paper(Ⅲ), the following equation of solvent effect in organic chemistry was suggested:
Ei=a﹒Ai(1-Va﹒VAi)+d﹒Di(1-Vd﹒VDi)+E0
Where Ei is a physical or chemical property of the substrate in the solvent i and E0 is that in n-hexane. Ai and Di are constants of electron acception and donation effect of the solvent i respectively. VAi and VDi are constants of electron acception and donation space effect of the solvent i respectively, a and d are the sensitivities of E of the substrate vs the change of Ai and Di. Va and Vd are the constants of electron acception and donation space effect of the substrate respectively. In IR spectra E could be substituted by the wavenumber(ν). Ai and VAi have been established for 18 organic solvents (n-C6H14, n-C7H16, cyclohexane, CCl4, Ph-Me, ClCH:CCl2, Et2O, CHCl3, C6H6, CH2Cl2, ClCH2CH2Cl, Ph-NO2, THF, 1,4-dioxane, Et-NO2. MeCO2Et, Me-NO2, Me-CN).
In this paper Di and VDi have been established for these solvents. The equation also has been tested by the νC-X(X=Cl, Br) of five alkylhalides (t-BuCl, n-C5H11Cl, t-BuBr, Et-Br, EtC(H)BrMe) and νC=O of three carboxyl compounds (t-BuCOMe, Me2CO, MHB) and seven organotin compounds [(Ph2MeSiCH2)3SnO2C-C6H4-X-p(X=H-, CH3-, CH3O-, NO2-, F-. Cl-, I-)].
The relationship (ν=ρ﹒σ+ν0) between νC=O of organotin compounds and Hammett constants(σ) of the substituted groups in different solvents was studied and a relationship betweenρ and Ai, VAi, Di, VDi of the solvents was found.     

DUSY沸石催化α-蒎烯异构化的溶剂化效应

脱铝超稳Y沸石(简称DUSY)催化α 蒎烯异构化反应是固 液多相催化反应。α 蒎烯是松节油的主要成分,具有特殊的双环双键结构。DUSY是八面沸石经改性后的固体酸催化剂,它主要用于石油化学工业的精细化学品的合成。我们曾报道了DUSY沸石催化α 蒎烯的异构化反应及其动力学特征[1 3]。本文研究了脱铝超稳Y沸石(DUSY,SiO2/Al2O3=8 61)在介电常数不同的溶剂中催化α 蒎烯异构化反应,考察了在不同溶剂中,反应时间、温度对转化率、产物分布的影响。结果表明,采用介电常数较大的极性溶剂四氢呋喃,对反应更为有利。1　实验部分1 1　原料…     

C60-甲苯溶液溶剂化作用

The solvation of the system of C60-toluene is studied by determining UV-Vis absorption spectrum, it is found that the maximum absorption wavelength of C60 exhibits red-shift in toluene medium. Viscosity measurement gives the thickness of the solvation layer as 0.85 nm. At temperature 30℃, the value of the diffusion coefficient is 3.12× 10-10m2•s-1 which is an order of magnitude less than that of small molecules. The results above indicate that C60 is solvated in toluene medium.     

The Interplay between Steric and Electronic Effects in SN2 Reactions

Myths of steric hindrance : In contrast with current opinion, energy decomposition analysis shows that the presence of bulky substituents at carbon leads to the release of steric repulsion in the transition state shown in the graphic. It is rather the weakening of the electrostatic attraction, and in particular the loss of attractive orbital interactions, that are responsible for the activation barrier.

     

Steric retardation of SN2 reactions in the gas phase and solution

The gas-phase S(N)2 reactions of chloride with ethyl and neopentyl chlorides and their alpha-cyano derivatives have been explored with B3LYP, CBS-QB3, and PDDG/PM3 calculations. Calculations predict that the steric effect of the tert-butyl group raises the activation energy by about 6 kcal/mol relative to methyl in both cases. Solvent effects have been computed with QM/MM Monte Carlo simulations for DMSO, methanol, and water, as well as with a polarizable continuum model, CPCM. Solvents cause a large increase in the activation energies of these reactions but have a very small differential effect on the ethyl and neopentyl substrates and their cyano derivatives. The theoretical results contrast with previous conclusions that were based upon gas-phase rate measurements.     

Comment on “The Interplay between Steric and Electronic Effects in SN2 Reactions”

We respond to a paper by Fernández, Frenking, and Uggerud (FFU: Chem. Eur. J. 2009 , 15, 2166) in which they conclude that not steric hindrance but reduced electrostatic attraction and reduced orbital interactions are responsible for the S_N2 barrier, in particular in the case of more highly substituted substrates, for example, F^? + C(CH₃)₃F. We disagree with this conclusion, which we show is the result of neglecting geometry relaxation processes that are induced by increased Pauli repulsion in the sterically congested S_N2 transition state.     

SN2 Reactions at Tertiary Carbon Centers in Epoxides

Described herein is a novel concept for S_N2 reactions at tertiary carbon centers in epoxides without activation of the leaving group. Quantum chemical calculations show why S_N2 reactions at tertiary carbon centers are proceeding in these systems. The reaction allows flexible synthesis of 1,3‐diol building blocks for natural product synthesis with excellent control of the relative and absolute configurations.     

Activation Strain Analyses of Counterion and Solvent Effects on the Ion-Pair SN2 Reaction of and CH3Cl

We have computationally studied the bimolecular nucleophilic substitution (S_N2) reactions of M_nNH₂⁽ⁿ⁻¹⁾ + CH₃Cl (M⁺ = Li⁺, Na⁺, K⁺, and MgCl⁺; n = 0, 1) in the gas phase and in tetrahydrofuran solution at OLYP/6-31++G(d,p) using polarizable continuum model implicit solvation. We wish to explore and understand the effect of the metal counterion M⁺ and of solvation on the reaction profile and the stereochemical preference, that is, backside (S_N2-b) versus frontside attack (S_N2-f). The results were compared to the corresponding ion-pair S_N2 reactions involving F⁻ and OH⁻ nucleophiles. Our analyses with an extended activation strain model of chemical reactivity uncover and explain various trends in S_N2 reactivity along the nucleophiles F⁻, OH⁻, and , including solvent and counterion effects. © 2019 Wiley Periodicals, Inc.     

两个Menschutkin反应溶剂效应的比较

Menschutkin反应是研究得较多的亲核取代反应之一,对溶剂的动力学效应也进行了广泛和深入的研究,并获得了巨大的成功,但因溶剂对反应速率的影响因素众多,且又错综复杂。     

应用分子形貌理论研究类SN2反应

应用分子形貌理论, 研究了类SN2反应过程中的沿着IRC路径上固定点的分子形貌的特征, 计算给出了形状和电子密度特征参数以及各键的Dpb值. 应用Matlab程序绘制了分子特征边界轮廓上的电子密度分布的三维图像, 即分子形貌像, 给出了这类反应的动态变化过程.     

Solvent effects on SN2 reaction between substituted benzyl chloride and chloride ion

The effects of solvent on S_N2 reaction between some substituted benzyl chlorides and chloride ion have been investigated by DFT and ab initio methods using the polarizabale continuum model. The activation energies are higher in the solution media relative to the gas phase and grow by the increase in the dielectric constant of solvent. The complexation energies in solution media are smaller than those in the gas phase and reduce with increasing the dielectric constant. The energy data are in good agreement with the geometrical parameters and substituent constants. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011