氟烯的结构-特性关系——8.建立自旋离域参数σ的新途径

取代基可以通过三种效应影响自由基型反应的速度,即:立体、极性和自旋离域化效应。离子型反应中没有自旋离域化问题,但在自由基型反应中,由于过渡态的能量直接受到极性作用和自旋离域化作用的影响,所以要拆分这两种作用,建立一套只反映能使自由基通过离域而稳定化的σ参数,就十分困难。近年来,化学工作者仍为此而继续努力,如     

何谓Y-芳香性

一谈到芳香性自然会联想到环状共轭体系。诸如苯、轮烯(中性分子或离子)及其同系物。由于它们具有特定的封闭层电子结构,π(p)电子沿环式周边离域而赋予体系一定的稳定化作用,一般说其周边的π(p)电子数符合Huckel(4n 2)规则。此外,分子轨道通过空间相互作用也可以使π(p)电子离域,从而产生一定的稳定化作用。由此又引伸出了同芳香性(homoaromaticity)与双环芳香性(bicycloaromaticity)。前者的π电子数符合Huckel(4n     

聚苯胺的质子酸掺杂机制的研究

木文用FT-IR、ESR、XPS等研究了聚苯胺的质子酸掺杂机制。结果表明聚苯胺掺杂时的质子化反应优先发生在分子链中的醌亚胺结构单元的氮原子上,并产生了分子内氧化还原反应而形成阳离子自由基。质子所带的电荷由于共轭作用能较好地离域到邻近苯环及对位氮原子上。     

多烯链平均π电子离域能的递变函数研究

离域能或共振能ED是一个共轭多烯体系中π电子能Eπ与相应数目n个孤立乙烯双键中π电子能总和nEπ之差量[1],即ED=Eπ-nEπ(c=c),由于离域能随双键数目增加而逐渐增大,大小不同的多烯链化合物总离域能不便比较.蒋明谦曾提出了著名的有机结构型性能的同系线性规律,他用多烯链每一个碳碳键上的平均离域能(或每个碳碳双键上的平均离域能)对同系因子(1/α)2/n作图,发现二者均具有良好的直线关系,如H(CH=CH)nH系列,碳碳双键上的平均离域能与同系因子成线性关系,相关系数为0.994,H(CH=CH)nC+H2系列,碳碳键上的平均离域能与同系因子线性相关,相关系数亦为0.994[2].但对于不同系列而言,碳碳键上的离域能和碳碳双键上的离域能不便比较.     

杂化电子的离域和轨道杂化的起因

从杂化电子离域的角度讨论轨道杂化的产生,提出电子交换是轨道杂化的根本原因。同时提出分子相对离域能和绝对离域能的概念及计算方法,说明相邻原子轨道之间的电子离域对体系稳定的重要性,并用电子离域的观点对杂化分子的许多现象进行了解释。     

对取代苯Ph—X（X=—f,OH,NH2）的价键理论研究

采用键表酉群方法对Ｃ６Ｈ５Ｆ，Ｃ６Ｈ５ＯＨ和Ｃ６Ｈ５ＮＨ２中的电子离域现象进行了计算和分析，讨论了取代苯的价键描述特性，并计算了取代基的π电子离域能。结果表明离子结构成分与离域能有直接关系。即离子成分越，电子高域能越大。     

环戊二烯分子内π电子的离域是失稳定的——分子内π和σ轨 …

为环戊二烯分子中非平面片断的片断轨道的建立提供了一个新的方法和计算程序。分子内的Ｍｏｒｏｋｕｍａ作用能的计算表明,“π电子的离域是失稳定的”与“离域的π体系是失稳定的”是两个完全不同的概念。π电子离域的结构效应完全取决于σ体系对离域的作用。     

环戊二烯分子内π电子的离域是失稳定的--分子内π和σ轨道分离法

为环戊二烯分子中非平面片断的片断轨道的建立提供了一个新的方法和计算程序 .分子内的Morokuma作用能的计算表明 ,“π电子的离域是失稳定的”与“离域的π体系是失稳定的”是两个完全不同的概念 .π电子离域的结构效应完全取决于 σ体系对离域的作用 .在环戊二烯分子中 ,π电子的离域和离域的π体系均是失稳定的 .在苯分子中 ,π电子的离域是失稳定的 ,它的离域π体系也是失稳定的 .但在 D6 h中 ,离域 π体系是“较小失稳定”的 .应该强调 π与 σ电子间空间作用对分子性能的重大影响 ,以改变经典有机结构理论重 π轻 σ电子效应的研究模式     

轨道去除方法及其应用

介绍了能对正碳离子及硼烷化合物中的电子离域现象作定量研究和分析的轨道去除方法 .一般的分子轨道方法能得到电子离域体系的波函数 ,而轨道去除方法则能得到电子离域效应被湮灭之后的假想定域体系的波函数 .通过对两者的对比分析 ,可定量而又清晰地了解分子内的电子离域是如何影响分子结构、能量及其他分子性质的 .具体讨论了正碳离子中烷基的超共轭现象和三卤化硼的Lewis酸性 .结果表明 ,轨道去除方法可非常有效地解释一些传统的化学问题     

锇杂苯的电子结构及芳香性

使用密度泛函理论及片段轨道相互作用分析方法,研究了典型的锇杂苯的电子结构和芳香性.结果表明,锇碳六员环具有较好的环平面性及键的离域性,占据的锇dxz轨道与碳环的3π空轨道之间的反馈π键相互作用,使得环上离域π电子数满足Hückel的4n+2规则,计算的环外质子化学位移、同键反应芳香性稳定化能、绝对硬度和磁化率增量数据均表明锇杂苯具有芳香性.     

磁场对铁氰化钾与抗坏血酸反应速率的影响

科学实验表明,磁场能改变水系及非水体系的许多物理化学性质,这不仅导致越来越多的科学的工作者对相关的理论问题进行了广泛和深入的研究^[1-4],而且还产生了一系列磁应用技术。从60年代至今,磁场及磁处理技术已在工业、农业、石油开采、混凝土、生物等领域得到了广泛应用^[5-8]。因磁场能改变水及水系的物理化学性质,如果对水系中进行的同一反应,磁场能改变其溶剂效应,则必然引进化学反应速率的改变。基于这种思想,前文^[9,10]曾采用磁处理反应液及磁场直接作用反应体系的方法对水溶液中进行的乙酸乙酯皂化反应体系的方法对水溶液中进行的乙酸乙酯皂化反应的速率常数进行了研究。结果表明,在最佳磁处理和最佳磁场条件下,该反应的速率常数都明显增大。铁氰化钾被抗坏血酸还原也是一个在水溶液中进行的而且其机理研究也较为成熟的反应。本文将采用磁场直接作用于反应体系的方法,研究不同的磁场条件对该反应速率常数的影响。     

强磁场对四苯基卟啉及其Co(Ⅱ)/Zn(Ⅱ)配合物的影响

为研究强磁场对卟啉类化合物的影响,以四苯基卟啉(TPP)为研究对象,比较分析了无外加磁场和强磁场条件下TPP的结晶,及Co~(2+)、Zn~(2+)与TPP的配位反应。采用X射线粉末衍射测试不同磁场强度下获得的TPP晶体,紫外分光光度计快速测定了不同磁场强度下配合物产率,并分析了配位反应的动力学。TPP的结晶度随磁场强度的增强而提高,晶体尺寸随磁场强度的增加而增大;随磁场的增强,四苯基钴卟啉(CoTPP)和四苯基锌卟啉(ZnTPP)的产率下降,但两者的反应动力学不受磁场影响,其反应速率随磁场强度提高而下降。由研究结果可知,强磁场有利于四苯基卟啉的结晶取向,四苯基卟啉在溶液中垂直于磁场取向是配位反应速率降低的主要原因,随磁场强度的增加,四苯基卟啉的取向程度提高。     

Magnetic field effect on chemical wave propagation from the Belousov-Zhabotinsky reaction

Effects of magnetic field (maximum field, 4 and 93 T(2) m(-1)) on the propagation speed of a chemical wavefront from the Belousov-Zhabotinsky reaction were studied in a thin glass tube. The downward and upward speed and the horizontal one are, respectively affected significantly by vertical and horizontal magnetic fields. Observations of the wavefront shape in magnetic fields showed that the magnetic force-induced convection causes the observed effects.     

A significant impact of Carreau Yasuda material near a zero velocity region

This goal of this study is to examine the incompressible steady 2D flow of MHD Carreau Yasuda model along with the heat generation and chemical reaction near a zero velocity region. The magnetic field and thermally conducting fluid towards a stretching cylinder are very significant due to its usage in the various manufacturing sector. Chemical reactions are widely practice in everyday life as turning nutrition into energy fuel for our body, food change, fireworks expulsions, removing grimes, photosynthesis, etc. The nonlinear flow model equations and their corresponding boundary conditions are changed into non-dimensional shape using similarity variables. The role of vital parameters is discussed with the assistance of MATLAB software by BVP4C method. It is concluded that the momentum increases for rising the curvature and stretching ratio parameter. This is examined that the heat field improves for rising behavior of the magnetic force, curvature coefficient and heat generation. The fluid concentration upsurges due to curvature and magnetic field parameter while reverse results shown due to chemical reaction parameter. We graphically investigate the impression of magnetic effect and chemical force for heat and mass profiles.     

Radio frequency magnetic field effects on a radical recombination reaction: a diagnostic test for the radical pair mechanism

The photoinduced electron-transfer reaction of chrysene with isomers of dicyanobenzene is used to demonstrate the sensitivity of a radical recombination reaction to the orientation and frequency (5-50 MHz) of a approximately 300 muT radio frequency magnetic field in the presence of a 0-4 mT static magnetic field. The recombination yield is detected via the fluorescence of the exciplex formed exclusively from the electronic singlet state of the radical ion pair Chr*+/DCB*-. Magnetic field effects are simulated using a modified version of the gamma-COMPUTE algorithm, devised for the simulation of magic angle spinning NMR spectra of powdered samples. The response of a chemical or biological system to simultaneously applied radio frequency and static or extremely low-frequency magnetic fields could form the basis for a diagnostic test for the operation of the radical pair mechanism that would not require prior knowledge of the nature and properties of the radical reaction.     

Magnetic field assisted Fenton reactions for the enhanced degradation of methyl blue

Magnetic field was tentatively introduced into Fenton reactions system for the degradation and discoloration of methyl blue as the represent of organic chemical dye,which was a bio-refractory organic pollutant in industry wastewater.It was found that under optimal Fenton reaction conditions,with the assistant of magnetic field in Fenton reactions,the degradation rate of methyl blue,the decomposition rate of H_2O_2 and the conversion rate of Fe~(2+)were accelerated,the extent of them would be improved by ...     

In Situ and Ex Situ Low‐Field NMR Spectroscopy and MRI Endowed by SABRE Hyperpolarization

By using 5.75 and 47.5 mT nuclear magnetic resonance (NMR) spectroscopy, up to 10⁵‐fold sensitivity enhancement through signal amplification by reversible exchange (SABRE) was enabled, and subsecond temporal resolution was used to monitor an exchange reaction that resulted in the buildup and decay of hyperpolarized species after parahydrogen bubbling. We demonstrated the high‐resolution low‐field proton magnetic resonance imaging (MRI) of pyridine in a 47.5 mT magnetic field endowed by SABRE. Molecular imaging (i.e. imaging of dilute hyperpolarized substances rather than the bulk medium) was conducted in two regimes: in situ real‐time MRI of the reaction mixture (in which pyridine was hyperpolarized), and ex situ MRI (in which hyperpolarization decays) of the liquid hyperpolarized product. Low‐field (milli‐Tesla range, e.g. 5.75 and 47.5 mT used in this study) parahydrogen‐enhanced NMR and MRI, which are free from the limitations of high‐field magnetic resonance (including susceptibility‐induced gradients of the static magnetic field at phase interfaces), potentially enables new imaging applications as well as differentiation of hyperpolarized chemical species on demand by exploiting spin manipulations with static and alternating magnetic fields.     

Bifurcation transitions in a photochemical system under low magnetic fields

In the last decades, the effect of low magnetic fields on biochemical and chemical systems has been an urgent problem. By now numerous experimental and theoretical studies have been conducted to demonstrate that commonly this effect is of no essence as it does not exceed 10%. However, there are experimental works which testify that in some systems, magnetic field effects are more significant. Thus, of great interest is an active search for rather simple but realistic models that are based on physically explicit assumptions and able to account for a strong effect of low magnetic fields. The present work not only offers a theoretical study on the simplest photochemical system, describing a reversible reaction of photodissociation, but also shows how a low magnetic field can strongly modify its properties under highly nonequilibrium conditions. It is assumed that external magnetic field can have effect on the rates of radical reactions occurring in a system. This, in turn, leads to bifurcation of the nonequilibrium stationary state and, thus, to a drastic change in the properties of chemical systems (temperature and reagent concentration).     

Conceptual DFT based electronic structure principles in a dynamical context

Within the context of quantum fluid density functional theory diverse processes simulating a chemical reaction like interaction of an atom or a molecule with an externally applied electric or magnetic field or its collision with a proton have been analyzed in a dynamical situation. The changes produced in the chemical reactivity parameters namely chemical potential, hardness, polarizability during such processes have been identified and discussed. In addition, confinement is also introduced to observe the necessary variation in the different reactivity parameters.     

丁烯醛与聚乙烯醇的缩醛化反应机理

化学分析法及碳核磁共振研究表明 ,作为不饱和醛的α 丁烯醛 (巴豆醛 )与聚乙烯醇在水溶液中进行缩醛化时存在着 1,2 加成与 1,4 加成两种反应方式 .此机理不同于只有 1,2 加成方式的聚乙烯醇缩饱和醛化反应 .1,4 加成主要导致聚乙烯醇缩丁烯醛的交联 .还提出了根据化学分析结果计算聚乙烯醇缩丁烯醛的缩醛度以及这两种加成方式的分率的方法