铜催化的共轭硅化反应的研究进展

有机硅化合物在有机合成中具有广泛的应用.它可以经过简单的反应转化为一系列的功能性的化合物.铜催化的不饱和化合物的共轭硅化反应是一种重要的合成有机硅化合物的方法.综述了铜催化的不饱和化合物的共轭硅化反应的发展过程及用于硅化反应的硅试剂的发展历程,重点总结了近些年的相关报道,尤其是不对称共轭硅化反应的进展.     

如何教给同学系统的，巩固的化学基础知识

在中学化学教学大纲上指示,中学化学教学的基本任务:“第一就是使学生获得一定的系统的和巩固的化学基本知识……。”我觉得这样的要求是非常恰当的。系统的鞏固的化学基本知识,就不是零碎的、片面的、散乱的一堆化学材料,而是系统的、科学的、自然界物质变化的规律;不是无用的、累赘的、死板的知识,而是学了化学之後,能获得合乎高等学校要求的化学基础,或是直接为国家的生产建设服务。因而在正确的进行系统的、鞏固的基本化学知识的讲授     

编者的话

在过去几年中,化学通报,无论在质的方面或量的方面,都有不少的进步,在这里边,作者的支持和读者的关怀,都起了很大的作用。值此新年佳节,我们谨向作者和读者祝贺并致谢意。“中国共产党第八次全国代表大会关于政治报告的决议”里指出了文化教育以及科学事业的发展,对于国家工业化的重要性。在周恩来同志的“关于发展国民经济的第二个五年计划的建议的报告”里,也把提高高等教育的和中等教育的质量作为一项任务。化学通报的主要服务对象,仍然和过去一样,是中等学校教师和大中学生。它的质量的高低,对于国家当前的任务完成的好坏,有直接的影响。我们愿和全国的化学工作者,共同努力,把通报的质量,进一步提高。     

DNA上电荷转移的理论研究

DNA上电荷的转移过程对许多生物化学和生物物理过程起着相当重要的作用，而本论文的主要研究方向即是利用动力学的方法发展双链模型研究DNA上电荷转移过程。根据已有的donor-bridge-acceptor模型的基本想法，论文给出了双链模型的哈密尔顿算符，解释了环境振子哈密尔顿算符与总的哈密尔顿算符中耦合项的关系。在双链模型的计算中，获得了良好的电荷密度衰减曲线。在对桥链长度变化的计算中，得出具有3或4个碱基对的桥链作为电荷转移机理的转折点，在这个折点两边的不同桥链长度的DNA链具有不同的衰减常数。而在对序列变化的计算中，可以看出，由于碱基之间的转移积分的差异导致了不同序列的链上电荷转移速度具有明显的差异，但是这种差异要远小于由于桥链长度不同而带来的速率的快慢。     

1997年全国高中学生化学竞赛(初赛)试题与试题分析

今年的全国高中学生化学竞赛的初赛刚刚结束。我们认为这次竞赛的试题较好地体现了今年5月全国高中学生化学竞赛工作会议上再次肯定的试题的水平要求:原理水平大致与人民教育出版社的《化学读本》相当,基本上不涉及更高一级的,即大学化学的原理,但考虑到冬令营的优胜选手以及参加国际竞赛的选拔,需要补充一定量的静态立体化学的知识(包括立体异构),当然试题涉及的具体化学内容本身对中学生是陌生的,但用竞赛学生的已有知识以及适当增加的知识为基础是可以理解的。为进一步考察试题的难易,我们对试题作如下的分析。     

物质的量的测量向摩尔溯源的标准

1 物质的量的基本单位——摩尔 物质的量的基本概念起源于完全确定的化学物质的本质属性—一存在的数目,换句话说起源于物质的特殊性质。按照这种理解表示“量”的最简单的方法就是指示所研究物质的粒子个数。单元是表述物质微粒数的一个合适的单位。然而,由于处理很大的数不方便,就选用了一个大的微粒数,组成一个     

结构化学展望

结构化学是探讨化学物质的微观结构以及它和宏观性能之间相互关系的基础科学,是化学学科的一个重要分支。这里所谓微观结构,指的是原子-分子层次的结构,包括分子中原子的空间排列以及原子基团之间的相对空间排布;分子的各种内部运动,包括分子的转动,原子间的振动和其中电子的运动;这些不连续的(即量子化的)运动状态给出的能级的分布。经典的化学结构理论曾经正确地指出:物质的内部结构完全决定了它的典型化学反应性能(实际上也同时决定了大部分其它方面的性能);反过来,通过这些典型化学反应性能的研究,原则上也应该能定出化     

从高考化学实验题的特点谈实验复习要"形神"兼备

随着高考改革的深入,能力考查的比重将越来越大。而实验题又正是综合能力考查的首选题型之一。对实验题的特点及导向进行分析会有效地提高化学实验复习的质量。1高考化学实验题的特点及导向分析近几年高考化学实验的都具备以下共同的特点:(1)形式上不再出现大型装置的连接,均是小型的又带有研究性的试题。(2)命题的立意上往往用常规搭建平台考查创新。如2002年化学实验的考查,既有氨气的制备方法的常规考查,又有喷泉实验装置的改进创新;2003年的既有制氢氧化亚铁的常规考查,又有氢氧化亚铁的制取的改进和创新。(3)重操作细节的考查。如2002…     

泽林斯基学派底发展道路(一)

一、烃类的合成二、烃的相互转变三、关于石油成因的研究四、■■类的催化反应五、硫化物的催化反应六、关于蛋白质化学的研究社会主义劳动英雄,泽林斯基院士是苏联著名的化学家。他曾经领导过卓越的化学学派,在碳氢化合物化学的研究中表现了出色的成就,他也是有机化合物催化反应创始人之一,对於苏联的有机化学工业作出了杰出的贡献。他发明了防毒面具,在第一次世界大战中拯救了十万人的生命。此外,在一、烃类的合成二、烃的互相转变三、关于石油成因的研究四、杂环类的催化反应五、硫化物的催化反应六、关於蛋白质化学的研究     

11R(-)-双氢青蒿酸的分离鉴定和青蒿酸的同位素标记

青蒿素是中药青蒿抗疟的有效成份。青蒿素不仅具有新颖的倍半萜结构,而且又有突出的抗疟药效。我们小组进行了它的生物合成的研究,以了解自然界合成这类物质的途径,生物合成中间体的分离鉴定,中间体的同位素标记和标记了的中间体的生物转化是生物合成研究的     

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.     

氢气在炭狭缝微孔内吸附的预测

通过边界的平均场近似,推导二平板狭缝孔格子理论Ono-Kondo吸附等温方程.利用格子气模型特性和微观物理学理论,计算氢分子在石墨平面的最大吸附容量.比较由氢分子在石墨平面二典型聚集状态标定的Ono-Kondo方程,并用预测精度较高的方程计算了与文献相同条件下的吸附等温线.在比较了计算结果、试验结果和GCMC分子模拟结果后,对Ono-Kondo吸附等温方程的特点、理论基础作了分析,指出了方程的适用范围.     

液晶聚合物/柔性链聚合物共混体系相分离形态

利用元胞动力学方法在二维情况下对浓度、取向序参量的含时Ginzberg-Landau方程进行数值求解,研究了液晶聚合物/柔性链聚合物共混体系的相分离动力学,考察了浓度、取向有序过程的耦合对相分离形态的影响.结果表明,此耦合作用对相分离的时间进程以及相分离图样的空间排布都有影响.液晶聚合物的取向有序相当于增加了两组分间的不相容性而促进两相分离;两个序参量在热力学方面的耦合使液晶聚合物趋向于沿着界面方向取向,而动力学方面的耦合使液晶聚合物分子沿着其取向方向扩散,相分离图样的空间排布由这两种效应共同决定通过极化率张量的定义用数值方法模拟得到了相分离体系的小角光散射图样,结果表明,散射强度分布具有方位角依赖性,它是由浓度、取向序参量的空间变化共同决定的.     

LOW DENSITY POLYETHYLENE/CLAY NANOCOMPOSITES MODIFIED BY ETHYLENE COPOLYMERS： EFFECTS OF FUNCTIONALIZED SEGMENTS ON MORPHOLOGY

Melt extrusion was used to prepare binary nanocomposites of ethylene copolymers and organoclay and trinary nanocomposites of low-density polyethylene （LDPE）, ethylene copolymer and organoclay. X-ray diffraction （XRD） and transmission electron microscopy （TEM） were used to analyze the structure of the clay phase and the morphology of the nanocomposites. Influences of the comonomer in the copolymer and the content of the copolymer on the morphology of the resulting nanocomposites were discussed. The binary and the trinary composites may form intercalated or exfoliated structures depending on the interaction between the copolymer and the clay layers and the content of the copolymer.     

Bimodality of molecular mass distribution of polydienes obtained under the action of dilithium initiators in hydrocarbon media: the reasons,mathematical simulations,and their experimental testing

Bimodal molecular mass distribution (MWD) of polymers, obtained upon polymerization of hydrocarbon monomers in the nonpolar media under the action of dilithium initiators, is the consequence of separation of the reaction mixture into two phases. Bifunctional /living/ oligomers produce the insoluble sediment due to tetrameric association of the lithium active sites (the swollen gel-fraction). Part of the active site remains in the solution (the solfraction). Difference in the concentrations of the active sites into the phases leads to difference between the propagation rates of the /living/ chains and, as a result, to Bimodal MWD. The mathematical model of polymerization in the two-phase system is proposed. Satisfactory agreement between the calculations and the experiments is shown for butadiene polymerization in heptane under the action of 1,4-dilithiumpentane. Regulation of MWD up to the complete elimination of bimodality is possible via the programmed dosage of monomer and solvent into the reactor.     

Investigations of the Mechanism of Alternating Copolymerization with Charge-Transfer Interaction of the Monomers

The applicability of the method of Giese to the measurement of the influence of monomer reactivity is examined. The reaction of alkyl mercuric salts with sodium borohydride permits the production of alkyl (cyclohexyl and butyl) radicals. Since hydrogen radicals are present in high concentration, the addition of alkenes to the reaction mixture leads to radicals from the alkenes. Further addition of alkene (polymerization) can be nearly completely excluded in this way. The composition of the reaction products is determined by gas chromatography. The addition rate of the alkenes relative to styrene allows correlation with the e value of the Q-e scheme of Alfrey and Price. The method answers the question of how far addition of the monomer complex occurs in one step or as separate addition of both monomers during copolymerization in the presence of charge-transfer (CT) complexes of the monomers. The investigations are performed by using the styrene/acrylonitrile/ZnCl₂system, and it is demonstrated that the reactivity of the complexed     

Properties of aqueous solution of sodium glycocholate and a nonionic surfactant,and their mixtures

The micellar properties of aqueous binary mixed solutions of sodium glycocholate, NaGC, and octa-oxyethylene glycol mono-n-decyl ether, C₁₀E₈, have been studied on the basis of surface tensions, the mean aggregation number and the polarity of the interior of the micelles. The mean aggregation number, measured by steady state quenching method, decreased with the increase of the mole fraction of NaGC in the mixed system. The polarity of the interior, estimated by the ratio of first and third vibronic peak in a monomeric pyrene fluorescence emission spectrum, suggested that the hydrophobicity of intramicelles increased with the increase of the mole fraction of NaGC in the mixed system. These are considered to be caused by the differences in the chemical structure and the hydrophobic nature between NaGC and C₁₀E₈. The mean aggregation number and the polarity of the interior for each micelle near the CMC in lower total concentration of surfactants showed the tendency approaching those of pure micelle of the nonionic surfactant. This suggests that the ratio of NaGC in the initial micelles in the range of lower total concentration near the CMC is lower than that of the corresponding prepared mole fraction in the mixed system. This lower value was confirmed also from theoretical calculation of the ratio of NaGC at the CMC in the mixed micelle by regular solution treatment of Rubingh in the solution.     

Reliability and uncertainty in the estimation of p<Emphasis Type="Italic">K</Emphasis><Subscript>a</Subscript> by least squares nonlinear regression analysis of multiwavelength spectrophotometric pH titration data

When drugs are poorly soluble then, instead of the potentiometric determination of dissociation constants, pH-spectrophotometric titration can be used along with nonlinear regression of the absorbance response surface data. Generally, regression models are extremely useful for extracting the essential features from a multiwavelength set of data. Regression diagnostics represent procedures for examining the regression triplet (data, model, method) in order to check (a) the data quality for a proposed model; (b) the model quality for a given set of data; and (c) that all of the assumptions used for least squares hold. In the interactive, PC-assisted diagnosis of data, models and estimation methods, the examination of data quality involves the detection of influential points, outliers and high leverages, that cause many problems when regression fitting the absorbance response hyperplane. All graphically oriented techniques are suitable for the rapid estimation of influential points. The reliability of the dissociation constants for the acid drug silybin may be proven with goodness-of-fit tests of the multiwavelength spectrophotometric pH-titration data. The uncertainty in the measurement of the pK _a of a weak acid obtained by the least squares nonlinear regression analysis of absorption spectra is calculated. The procedure takes into account the drift in pH measurement, the drift in spectral measurement, and all of the drifts in analytical operations, as well as the relative importance of each source of uncertainty. The most important source of uncertainty in the experimental set-up for the example is the uncertainty in the pH measurement. The influences of various sources of uncertainty on the accuracy and precision are discussed using the example of the mixed dissociation constants of silybin, obtained using the SQUAD(84) and SPECFIT/32 regression programs.     

Chain dynamic parameters for some acrylic polymers

The dielectric relaxation data of Ishida et al. on a number of acrylic polymers are represented in terms of the relaxation function proposed by Havriliak and Negami using the multi-response techniques developed by Havriliak and Watts. Two of the parameters of this function are interpreted in terms of a temperature dependent distribution of relaxation times. In this method of interpretation the breadth of the distribution function is temperature-dependent while the skewness is not. The temperature dependence of the breadth of the distribution function is similar for most of these acrylic polymers.The parameters of the relaxation function are also interpreted in terms of Mansfield's model which represents intra- and inter-molecular interactions in terms of springs and dash pots. Briefly, increasing the side chain length for the methacrylate series increases the inter-molecular relaxation time which may be due to an increase in the entropy of activation for the orientation process. The difference between the one acrylate in this study and the four methacrylates of the series is a reduction in the intra-molecular relaxation time, apparently due to the lack of the alpha methyl group.