关于正规苯烃和正规晕苯烃的拓扑性质的研究

本文较系统地研究了正规苯烃和正规晕苯烃的拓扑性质,给出了Cyvin和Gutman于1986年提出的两个猜想的证明。这些拓扑性质的给出和猜想的证明对正规苯烃和正规晕苯烃的判定、产生、分类、计数以及合成和理论研究都有一定的意义。     

有机张力分子弯键特征的理论研究

提出了任意张力分子中弯键特征的计算公式，对一系典型的有机张力分子－单环烃、双环烃、螺桨烷、多面体烷及部分不饱和环状烃的结构、张力、稳定性及反应性之间的关系进行了研究，其弯键特征的理论研究表明，有机张力分子的Ｃ－Ｃ键均发生不同程度弯曲，且Ｃ－Ｃ弯键之间的的夹角与四面全杂化角度１０９．５℃的差值Δβ可成为有机分子张力与稳定性的量度。     

氯仿,乙醇,苯有关二元体系加压相平衡研究

氯仿、乙醇、苯有关二元体系加压相平衡研究马忠明，陈庚华，王琦，严新焕，韩世钧，余淑娴（浙江大学化学系，杭州，３１００２７）（江西大学化学系）关键词加压汽液平衡，醇烃体系，氯仿，乙醇，苯醇是极性分子，烃是非极性或弱极性分子，醇与醇、烃与烃分子及醇与烃分...     

直链饱和烃取代衍生物的标准汽化热的拓扑指数

直链饱和烃取代衍生物的标准汽化热的拓扑指数张秀利（河北轻化工学院基础部石家庄０５００１８）关键词汽化热拓扑指数ＺＧ中图分类号６２４．１１汽化热是反映液体分子间相互作用力大小的重要热力学参数。前人对其估算做了大量的工作［１－３］。这些方法大都未能很好地...     

支持向量机与KStar模型预测细胞色素P450酶催化的氧脱烃反应

分别以支持向量机(SVM)和KStar方法为基础, 构建了代谢产物的分子形状判别和代谢反应位点判别的嵌套预测模型. 分子形状判别模型是以272个分子为研究对象, 计算了包括分子拓扑、二维自相关、几何结构等在内的1280个分子描述符, 考查了支持向量机、决策树、贝叶斯网络、k最近邻这四种机器学习方法建立分类预测模型的准确性. 结果表明, 支持向量机优于其他方法, 此模型可用于预测分子能否被细胞色素P450酶催化发生氧脱烃反应. 代谢反应位点判别模型以538个氧脱烃反应代谢位点为研究对象, 计算了表征原子能量、价态、电荷等26个量子化学特征, 比较了决策树、贝叶斯网络、KStar、人工神经网络建模的准确率. 结果显示, KStar模型的准确率、敏感性、专一性均在90%以上, 对分子形状判别模型筛选出的分子, 此模型能较好地判断出哪个C―O键发生断裂. 本文以15个代谢反应明确的中药分子为验证集, 验证模型准确性, 研究结果表明基于SVM和KStar的嵌套预测模型具有一定的准确性, 有助于开展中药分子氧脱烃代谢产物的预测研究.     

烃同分异构体的计数

能否系统精确地解决高中化学学习中的同分异构体计数问题?本文在高中数学化学的背景知识之上,引入生成函数以及Pólya计数定理,在不考虑立体异构的前提下,从烷基的同分异构体计数入手,逐步推导烷烃、一烯烃、一炔烃苯的衍生物、二取代烷烃以及二烯烃的同分异构体计数的公式,并将计算结果与手工枚举进行对比,进一步证明其正确性。我们还归纳性地发掘了同分异构体计数的渐进特征并提出了以上烃类同分异构体计数的近似公式。对比国外的成果,本文尽力避免引入过多的数学概念,降低门槛,适合高中生阅读,加深对于烃结构的理解,培养计算思维;对比国内相同主题的研究,本文的推导形式清晰简洁,拓展性较强。     

烃及其衍生物气相色谱保留指数的定量结构相关性研究

在分子拓扑理论的基础上,定义了原子的价点价δYi,由δYi构建了一个能表征含多重键、杂原子化合物的结构信息价连接性拓扑指数mZY(m=0,1,…,n).发现1ZY与烃及其衍生物的气相色谱保留指数IR有良好的相关性.与其他的指数相比较,新指数的相关性优秀,且新方法还具有计算简单,物理意义明确等优点.对新模型采用Jackknife法予以检验,具有总体稳健性.     

石油饱和烃分子组成分析方法综述

高效利用石油资源和生产高质量石油产品要求从分子水平认识石油化学组成,而饱和烃作为石油中最主要的一类组分,其分子组成分析是石油化学研究的重要课题.总结了石油饱和烃的分子组成分析方法并简要介绍其应用,主要包括基于气相色谱技术的单体烃分析方法和基于质谱技术的分子/族组成分析方法.针对石油饱和烃的质谱电离技术,总结了各方法的技术优势及存在的问题,对相关技术和方法的发展前景给予展望.     

链烃,环状烃和多面体烃的定域分子轨道研究

采用GAUSSAN 80程序对一系列直链烷烃、环状烃和多面体烷烃进行STO-3G基组下的曲initio计算,在所得非定域分子轨道自洽场结果的基础上,利用Boys方法进行定域化,进而研究了这些分子的定域分子轨道的键弯曲性质、轨道能量和集居数与几何结构之间的关系,用上述结果对一些典型分子的稳定性进行了讨论。     

非交替烃HOMO、LUMO、LOMO能量计算

本文将前文~[1,2]建议的直接计算交替烃HOMO(最高占据分子轨道)、LUMO(最低未占分子轨道)能量的方法推广到非交替烃。在HMO近似内, 对非交替烃分子的邻接矩阵联合应用逆迭代和Rayleigh商, 只需迭代一次就能得到该分子HOMO(或LUMO)能量的足够精确的结果。文中提出了计算的格式, 说明了选择初始变分函数的原则。用这种方法, 计算了30个分子的前线轨道~[3]能量, 平均误差为0.002β。本文提出了计算LOMO(最低占据分子轨道)能量的拓扑公式, 它同时适用于交替烃和非交替烃, 其计算精度要优于文献中曾经报道过的结果。用例子说明了方法的应用。     

Study of the molecular mobility of collagen

The dielectric relaxations of a biopolymer, collagen, have been studied by means of the thermally stimulated current (TSC) technique. To investigate effects of water on TSC spectra, complementary measurements by differential scanning calorimetry (DSC) have been performed. In dehydrated collagen, three spectral bands were recorded in the temperature range of -180-60°C, labelled α, β₁, and γ in the order of decreasing temperature. The TSC spectrum of hydrated collagen exhibits a supplementary band labelled β₂. By using the fractional polarization method, the γ and β₁ modes have been attributed to localized movements of nonpolar (apolar) sequences and polar sequences, respectively. The α mode has been associated with delocalized movements of the collagen macromolecules. Finally the β₂ mode has been attributed to reorientations of bound water molecules inside the collagen fibers. © 1995 John Wiley & Sons, Inc.     

卟啉化合物的共振能

具有芳香性的卟啉环的共振能是卟啉类化合物的重要结构参数,据此可以讨论卟啉的光谱和化学反应性能等问题。本文根据分享键能(Contributing Bond Energy)的概念,对复杂分子卟啉的键能进行了计算。采用分享键能和键解离能(Bond Dissociation Energy)的差值,计算了某些卟啉化合物的共振能。计算方法简便,计算结果与以前文献报道的以及实验值符合。     

Thermoluminescence from photoexcited polyethylene terephthalate

Thermoluminescence from polyethylene terephthalate (PET) has been investigated. A correlation was found between thermoluminescence (TL) and thermally stimulated current (TSC). The apparent activation energy was estimated at 0.23–0.50 eV for both TSC and TL from ?170 to 0°C. This activation energy presumably indicates the trap depth, which is decreased by molecular motions, since both TSC and TL are quenched efficiently with visible light, but not with infrared light of energy of the magnitude of thermal activation energy. The spectrum of TL glow curves agrees with the photoluminescence spectrum at ?185°C, which is composed of an excimer and a monomer fluorescence and also a structured phosphorescence at wavelengths longer than 400 nm.     

Effect of catalysts on thermally stimulated current in poly(ethylene terephthalate)

The effect of catalysts on relaxation phenomena in poly(ethylene terephthalate) (PET) was studied by thermally stimulated current (TSC). Resins Sb-PET and Ge-PET were produced by the antimony and germanium main catalyst systems, respectively. Spontaneous, global and thermal sampling of TSC were compared in both PETs. The lower TSC peaks are observed in Ge-PET than those in Sb-PET for equivalent treatment. The compensation parameters were determined from the variation polarization temperatures (Tp) data. These parameters were used to calculate degree of disorder (DOD). The DOD of Sb-PET and Ge-PET were 36.14 and 66.23, respectively. The relaxation time at the maximum current and the dipolar relaxation strength in the Sb-PET has the higher values and wider distribution than that in Ge-PET. Furthermore, Sb-PET exhibited electrically softer. These results are attributed to the stiffening amorphous parts by the entanglement network in Ge-PET. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of the thickness and polarization charges on the electro-optical behaviour of twisted smectic C* cells

This paper reports on the influence of both polarization charges and thickness on the light transmitted by twisted smectic C* (TSC) liquid crystal (LC) cells. A uniaxial model, based on the de Vries eigenmodes usually used for twisted structures like cholesteric LCs, is used to calculate the transmission variation of the TSC cells as a function of applied voltage or thickness for various values of spontaneous polarization. The results obtained are in quantitative agreement with experimental results found in the literature and emphasize the importance of polarization charges on the behaviour of TSC cells. The TSC light transmission exhibits a profile resembling the so-called V-shaped switching.     

Mechanism of oxidations in partially aqueous media: Kinetics of oxidation of thiosemicarbazide and thiosemicarbazone by chloramine-T and dichloramine-T in aqueous methanol

Kinetics of oxidation of thiosemicarbazide (TSC) and its hydrazone (Benzaldehyde thiosemicarbazone) by chloramine-T (CAT) and dichloramine-T (DCT) in aqueous methanol medium in the presence of perchloric acid has been studied. Oxidation of TSC by both the oxidants showed first order dependences in [oxidant], fractional order in [TSC] and nearly inverse first order in [H⁺]. The conversion of TSC into its benzaldehyde hydrazone changed the rate dependence in [CAT] from first to second order, while the dependence in [DCT] remained unchanged. The dependence in [TSC] changes from fractional order to zero order in both CAT and DCT oxidations. The rate followed inverse fractional order kinetics in [H⁺] in both the cases. Increase in ionic strength of the medium slightly decreased the rate, while the decrease in dielectric constant of the medium increased the rates of oxidations for both the oxidants. But the addition of reaction products, p-toluenesulphonamide and chloride had no effect on the rate. Oxidation of TSC with both the oxidants has been shown to follow Michaelis-Menten type mechanism. In hydrazone oxidations oxidants have been shown to disproportionate in slow steps to HOCl, which in turn attacks the substrate in fast steps to give the final products. [TSC] was varied at different temperatures and the constants of rate limiting steps were calculated at each temperature. Using the latter constants the activation parameters have been computed from the Arrhenius plots. The rate constants have been predicted from the rate law for the variation of [H⁺] at constant [TSC] and [oxidant]. The predicted values are in reasonable agreement with the experimental rate constants, providing additional support to the suggested mechanisms.     

Influence of the thickness and polarization charges on the electro-optical behaviour of twisted smectic C* cells

This paper reports on the influence of both polarization charges and thickness on the light transmitted by twisted smectic C* (TSC) liquid crystal (LC) cells. A uniaxial model, based on the de Vries eigenmodes usually used for twisted structures like cholesteric LCs, is used to calculate the transmission variation of the TSC cells as a function of applied voltage or thickness for various values of spontaneous polarization. The results obtained are in quantitative agreement with experimental results found in the literature and emphasize the importance of polarization charges on the behaviour of TSC cells. The TSC light transmission exhibits a profile resembling the so-called V-shaped switching.     

Theoretical study of the N---H tautomerism in free base porphyrin

The N---H tautomerism of free base porphyrin is investigated at the semiempirical spin-unrestricted AM1 (UAM1) and ab initio RHF/3-21G levels. The UAM1 method provides delocalized geometries for all stationary structures without imposing any symmetry constraint. RHF/3-21G geometry optimizations have to be performed under symmetry restrictions to ensure that realistic delocalized structures are obtained. Both the semiempirical and the ab initio calculations predict that the interconversion between trans tautomers proceeds in an asynchronous two-step process via intermediate cis tautomers. The cis tautomers are characterized as minima in the potential energy surface and are 8–10 kcal mol⁻¹ higher in energy. The activation energy for the trans → cis interconversion is calculated to be approximately 23 kcal mol⁻¹ at the 3-21G level. The activation energy for the synchronous trans → trans interconversion is higher and has a value of 30.5 kcal mol⁻¹. The activation energies obtained at the semiempirical UAM1 level are twice as large as the ab initio values.     

General properties of secondary relaxations in polymers as determined by the thermally stimulated current method

The method of thermally stimulated current (TSC) has been used to study the low-temperature dielectric β relaxations of several polymers including especially poly(vinyl chloride), poly(vinyl acetate), polyamide 6, 6,6,poly(t-butyl acrylate), poly(methyl methacrylate), poly(ethyl methacrylate), poly(phenyl methacrylate), and poly(t-butyl methacrylate). The distribution characteristics of the relaxation processes have been determined from the corresponding TSC peaks by a fractional polarization technique which consists of applying the electric field in several discrete steps during a slow cooling. Several common features have been found in all the polymers investigated: the β peaks are characterized by a distribution of relaxation times resulting from a distribution in activation energy and this distribution is quasisymmetrical and continuous. These facts are in agreement with the hypothesis of a relaxation involving local motions of small polar groups undergoing various interactions with the environment. Some discrepancy remains, however, between our calculated values of the mean activation energy and those obtained from the dielectric loss.