离子的极化和形变

离子的极化和形变是无机化学教学中的一对重要概念,这对概念可以用于解释化合物的结构及许多物理和化学性质。然而一些教科书在介绍这对概念时,大都把极化作用限于阳离子,把形变作用限于阴离子,而忽略了阴离子的极化作用和阳离子的形变作用。同时,在应用这对概念解释化合物结构和性质时,条理上也不十分清晰,甚至还出现自相矛盾的情况,使得学生在学习这对概念时感到困惑。本文介绍了离子的极化和形变这对概念的基本含义,讨论了影响极化能力和形变程度的因素,分析了一些化合物的结构以及溶解度、颜色和热稳定性等物理和化学性质。特别是对一些教学中有争议的问题给出了合理解释。在分析小分子结构时,极化和形变概念的运用可以弥补杂化轨道理论和价层电子对互斥理论的不足。     

Glycolate and Thioglycolate Complexes of Rhenium and Their Oxidative Elimination of Ethylene and of Glycol

Selenium dioxide and osmium tetroxide are effective reagents and catalysts for olefin oxidation, although, owing to their toxicity, reservations remain as to their applicability.^[1] We are therefore seeking more easily handled metal oxides that are soluble in organic solvents and that are as effective as osmium tetroxide in carrying out stereospecific cis hydroxylation of olefins. The rhenium(VII ) oxide 1 , which has meanwhile become readily accessible, is a favorable candidate.^[2]     

Advances and challenges of electrokinetic dewatering of clays and soils

The development of electrokinetic dewatering technologies for clay and soil materials has steadily advanced for over 100 years. A review of the origins, important contributions, and recent work on the topic are presented. Research into the electrokinetic mechanisms have informed the design process and resulted in prototypes and pilot-scale implementations that are economically viable additions to current processes. The power demand and availability of dimensionally stable anode materials are the current challenges to industrial adoption of electrokinetic dewatering.     

芴-噁二唑类聚合物的合成及光谱特性

通过缩聚反应,制得了高分子量的线型和超支化的芴-噁二唑类聚合物．它们均可溶于常用的有机溶剂。在固态薄膜时,它们的紫外-可见光吸收光谱在大约398nm和376nm处有两个强的吸收峰。它们的薄膜PL光谱在蓝光波长范围内有强发射峰,薄膜PL效率约为16％。电化学测试显示它们的的LUMO能级比芴的均聚物高,而与钙、镁这样典型的阴极材料的功函数较接近．这表明此类聚合物具有较好的电子注入和传输性能。     

The infrared spectra and structure of acetamide and acrylamide

The far-IR vapour phase spectra of acetamide and acrylamide are reported and several transitions in the amido “inversion” vibration are identified. The potential energy curves governing the vibration are deduced from the experimental data and are found to have a single broad minimum for both molecules, implying that the amido hydrogens are copianar with the N-CO atoms, but that the resistance to their out of plane displacement is small. The band contours found in the mid-IR spectrum of acrylamide suggest that the cis orientation of the two double bonds about the C-C single bond is favoured over the trans orientation; indeed no evidence of the latter has been found.     

立方烷和高立方烷类衍生物的合成及应用

以立方烷和高立方烷的发展过程为线索,详细地叙述了其合成过程,并阐述了相应的合成方法,针对立方烷及高立方烷的特殊结构特点,叙述了其目前作为含能材料和药物的主要应用状况,以及其可观的发展前景。     

三氯锗丙酸及其衍生物自组装单分子膜的制备与表征

首次制备了三氯锗丙酸及其酯类衍生物(Cl₃GeCH₂CH₂COOC_nH_2n+1,n=0,2,4,6)在羟基化的单晶硅片上的自组装单分子膜,并利用接触角测量、椭圆偏振和光电子能谱法进行结构表征.结果表明,这类分子的自组装行为与三氯硅烷相似,组装后在基底表面形成准二维锗烷网状排布;分子链轴有一定倾斜角;膜表面润湿性随表征液体和三氯锗丙酸尾链取代基不同而不同.     

Capillary electrophoresis and electrochromatography of pesticides and metabolites

Synthetic pesticides are important chemicals since they are widely used to control many types of weeds, insects, and other pests in a wide variety of agricultural and nonagricultural settings. This review article is aimed at describing the recent progress made in capillary electrophoresis (CE) and capillary electrochromatography (CEC) of pesticides and metabolites. The various electrophoretic systems and detection schemes that were introduced during the period extending from the second half of 1999 to the first half of 2001 for the CE and CEC of pesticides are discussed. Also included in this review article are the various approaches for trace enrichment that are involved in the analysis of dilute pesticide samples.     

Silica self-assembly and synthesis of microporous and mesoporous silicates

The microstructure of silica in basic aqueous solutions containing organic cations and prepared from monomeric precursors is reviewed and interpreted within the context of classical ideas of self-assembly of molecular aggregates. The solution properties can be understood by using the pseudo-phase separation approach coupled to the acid-base chemistry of silanol groups and the Poisson-Boltzmann equation. The silica nanoparticles frequently observed in these systems have a core-shell structure with silica in the core and the organic cations at the shell. Individual particles are observed when the forces between particles are repulsive-as is the case for small cations such as tetramethylammonium or tetrapropylammonium-and extended structures such as M41S materials are formed when the forces are attractive--as is the case for surfactants such as cetyltrimethylammonium. These ideas are useful to understand the evolution of zeolite synthesis gels from nucleation to crystal growth. Although at room temperature the silica and the organic cations are segregated, upon heating the organic cations are embedded within the particles. This transformation signals the onset of structure direction whereby the size and geometry of the organic cation induce changes in the structure of silica that may lead to zeolite nuclei.     

Capillary electrophoresis and electrochromatography of pesticides and metabolites

Synthetic pesticides are important chemicals since they are widely used to control many types of weeds, insects and other pests in a wide variety of agricultural and nonagricultural settings. This review article is aimed at describing the recent progress made in capillary electrophoresis (CE) and capillary electrochromatography (CEC) of pesticides and their metabolites. The various electrophoretic systems and detection schemes that have been introduced so far for the CE and CEC of pesticides are discussed. Also included in this review article are the various approaches for trace enrichment that are involved in the analysis of dilute pesticide samples.     

Investigation of adhesion and mobility of polyurethane and epoxy-rubber glues and adhesives

The values of activation parameters in uncured and cured epoxy resins, rubbers, and blends thereof are investigated. The dependences of activation energy and adhesion strength of epoxy-rubber compositions on rubber content are determined. The correlation of adhesion and activation energy values for polyurethane rubber and epoxy-rubber compositions is shown.     

Dynamic scattering properties of mixtures of cyclic and linear homopolymers and copolymers

The dynamic scattering properties of mixtures of cyclic copolymers and homopolymers are discussed. These properties are compared with those characterizing linear chain mixtures in similar conditions. The differences between cyclic and linear chains are introduced through the form factors only. The interaction parameter between different monomer species are assumed to be the same whether they belong to cyclic or linear chains. The dynamical model is based upon a generalization of the random phase approximation neglecting hydrodynamic interaction and mode coupling effects. Despite these simplifications, substantial differences are found in the dynamics of mixtures containing cyclic copolymers and homopolymers when compared to those of linear chain systems in similar conditions of temperature, concentration, and molecular weight. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35 : 1191–1200, 1997     

On-line and off-line preconcentration of trace and ultratrace amounts of lanthanides

The need for preconcentration of trace and ultratrace amounts of lanthanides from environmental, geological and biological samples is brought out in introductory part. Both on-line and off-line preconcentration procedures developed for lanthanides since 1980 are reviewed. The preconcentration techniques covered in this review include liquid-liquid extraction (LLE), ion-exchange, co-precipitation, and solid phase or solid-liquid extraction. Separate sections are devoted to each of the preconcentration techniques employed for enrichment of individual or mixtures of lanthanides. Future trends in singular or multielement preconcentration of lanthanides are also discussed.     

Molecular structure of mono- and dicarbonyls of rhodium and palladium

Summary Density Functional Theory has been applied to the study of the molecular structure of neutral and positively charged mono- and dicarbonyls of rhodium and palladium. The calculated optimized geometries, dissociation energies and normal frequencies are reported for the MCO, MCO⁺, M(CO)₂ and M(CO) ₂ ⁺ systems (where M=Rh and Pd), and the trends are discussed in detail. For neutral carbonyls, we interpret the M–C bond strength in terms of repulsion, which must be avoided, and attraction. These are related to the metal atom properties, such as the atomic splittings and the atomic ionization energies. In ionic carbonyls, the bonding is characterized by electrostatic attraction and repulsion. The rhodium carbonyls are generally found to be more stable than the corresponding palladium carbonyls. The palladium dicarbonyls are found to be linear, while both linear and bent structures are stable for rhodium dicarbonyls. An interpretation of these trends is made.     

The advantages and disadvantages of direct and indirect calorimetry

Kleiber's definitions of what constitutes direct and indirect calorimetry are accepted as the beginning of a commentary on the advantages and disadvantages of direct and indirect calorimetry in which calorimetry is divided into a number of categories based on the kind of calorimetric measurement. For non-reaction calorimetry such as entropy determinations and differential scanning calorimetry, the only means of measurement is by direct calorimetry. For reaction calorimetry, a preference of direct over indirect calorimetry depends on the accuracy needed and the ability of the experimenter to define the system. The data necessary to correct the observed heat loss in direct calorimetry are often all that are needed to make an indirect calculation of the true heat loss. In general, because they are convenient and inexpensive to use, indirect calorimetric methods are preferable to direct methods. However, when possible, one method can be used to verify the results of the other.     

Paradigms and Paradoxes: Aspects of the Energetics of Carboxylic Acids and Their Anhydrides

Making use of the enthalpies of formation of the well-established acetic acid and acetic anhydride, the energetics of other carboxylic acid anhydrides (with four or fewer carbons) are discussed. Some of these species are also well known, such as succinic and maleic anhydride. Others are less well known, such as ketene and carbon suboxide and even diatomic carbon and malonic anhydride. Still others are more evasive, such as the classical anhydrides of formic and oxalic acid.     

Synthesis and characterization of phospha-palladacycles and their catalytic properties in the olefination of chloro- and bromoarenes

Acetylacetonates of phospha-palladacycles are new catalysts in the Heck coupling of aryl chlorides and bromides with styrene. Turnover numbers (TON) of much higher than 300,000 and product yields up to 99% are obtained.     

Synthesis and electrooptical properties of triphenylamine- and oxadiazole-containing polymers

Soluble aromatic polyimides and copolyimides are synthesized on the basis of 4,4′-diaminotriphenylamine and oxadiazole-containing diamines. Poly(ester oxadiazoles) are prepared from acid dichlorides or oxadiazole-containing acid dihydrazides. The optical, electrochemical, and thermal properties of the polymers are investigated. It is shown that oxadiazole-containing polyimides and poly(ester oxadiazoles) are able to transfer electrons, while triphenylamine-containing polyimides and copolyimides can transfer holes and electrons.     

丙酮酸和苯甲酰甲酸热分解反应的速率常数

用从头算方法在6-31G的水平上研究了丙酮酸和苯甲酰甲酸热分解反应的机理．反应过程中各驻点都进行MP2相关能校准．计算结果表明：这两个反应都是羟基氢经历五元环过渡态迁移到α-羰基氧上形成氢键中间体;然后氢键中间体直接分解成异构体和二氧化碳;最后异构体经历三元环过渡态异构化成相应的醛．其中氢迁是决速步骤．在MP2／6-31G／／HF／6-31G基础上,对应于这两个反应速控步骤的活化位垒分别是186．0kJ·mol-1和169．3kJ·mol-1．在传统过渡态理论的基础上,计算了这两个反应在一定温度范围内热速率常数,理论的计算结果与实验值有很好的吻合．     

Mean amplitudes of vibration of molecules and ions with interhalogen bonds and related species

Mean amplitudes of vibration of molecules and ions containing interhalogen bonds are reviewed and critically analyzed. The presented information comprises pure interhalogen compounds as well as oxohalides. Correlations between mean amplitude values and structural and bond properties are discussed. Comparisons with data of related - specially isoelectronic - species are also performed. Characteristic ranges for the mean amplitudes of vibration for halogen-halogen and halogen-oxygen bonds could be established. The presented and discussed results are also of central importance for the analysis and interpretation of electron diffraction studies.