化学竞赛实验试题的内容与特点

本文针对全国化学竞赛（决赛）大纲实验部分和国际化学奥林匹克竞赛实验大纲的内容,分析了近年来全国高中学生化学竞赛（决赛）和国际化学奥林匹克竞赛实验试题。研究表明,近年来的竞赛实验试题呈现出了实验内容的社会化、实验手段的现代化、仪器的微型化和药品的微量化、以及实验过程要求绿色化等特点。     

全国化学奥林匹克竞赛研讨会会议纪要

由中国化学会主办的全国化学奥林匹克竞赛研讨会于7394年8月2日到8月6日在北京举行。这次会议是在全国化学竞赛开展了10年、我国参加国际化学奥林匹克竞赛8年之后,在第27届国际化学奥林匹克竞赛（27th IChO,1995.7,中国·北京）之前召开的总结经验,继往开来的大会。     

加拿大化学奥林匹克竞赛的特点及启示

加拿大化学奥林匹克竞赛（CCO）是以促进高中学生学习化学的兴趣为宗旨,以选拔国际奥林匹克竞赛选手为目的的考试,隶属于加拿大化学和物理奥林匹克竞赛（CCPO）活动的一部分。本文介绍了加拿大化学奥林匹克竞赛的概况,分析了部分试题的内容和考点,指出了试题的特点。     

高中化学竞赛与化学前沿研究的密切联系* ——以第32届全国化学奥林匹克竞赛(决赛)有机试题为例

通过详细解析第32届全国化学奥林匹克竞赛(决赛)第7和8道有机试题,让参加化学竞赛决赛的考生理解关注化学前沿研究的重要性,并指出如何快速检索出备考中所需要的文献,以及如何利用文献弥补知识漏洞。     

化学竞赛学生实验能力培养策略的研究

分析了近年来全国高中学生化学竞赛（决赛）和国际化学奥林匹克竞赛实验试题,从化学实验能力的表现和高中化学竞赛实验培训的实践出发,并结合认知规律,探讨了培养化学竞赛学生实验能力的策略。     

第31届全国化学奥林匹克竞赛(初赛)有机试题解析

从基础知识角度出发,对第31届全国化学奥林匹克竞赛(初赛)有机试题进行详细解析,供辅导化学竞赛的一线教师和参加化学竞赛的学生参考。     

《化学奥林匹克教育研究》课程建设探讨

一、《化学奥林匹克教育研究》课程建设的必要性中学化学竞赛活动有四个层次,即国际化学奥林匹克竞赛、全国化学奥林匹克竞赛、全国化学奥林匹克分赛区竞赛和全国初中化学奥林匹克竞赛（天原林）。化学竞赛活动在我国开展近十年,对我国化学教育事业起到了积极的作用。随着此项活动的开展,人们渐渐认识到“化学奥林匹克”不只是简单的竞赛活动,而是一种大规模的、不断进行着的、不同形式与不同层次的、系列的、以竞赛为中心的教育活动。准确地讲,应该称为“化学奥林匹克教育”。其目的是在发现和培养化学人才的同时,提高中学化学教育水…     

中学化学竞赛训练中几个问题的探讨

随着全国化学竞赛的开展,我国中学生在国际化学奥林匹克的赛场上捷报频传。这强烈地激发了广大青年学生的爱国热情和进取心,对于广大的化学教育工作者也是一种极大的鼓励和鞭策。     

化学竞赛的组织和指导

国际化学奥林匹克竞赛是中学生的世界规模和影响极大的学科竞赛活动之一。近年来,我国中学生在国际化学竞赛中捷报频传,大大地推进了国内化学竞赛的开展,使竞赛不断深化和不断进入新的层次。     

浅谈化学奥林匹克竞赛选手的选拔与培养

国际化学奥林匹克竞赛随着它日益增长的声望,参加的国家越来越多,是世界上最有影响的中学生化学竞赛活动。近年来,我国中学生在国际化学奥林匹克竞赛中捷报频传。     

Isotope Effects in Organic Chemistry and Biochemistry

The present article shows the extent to which isotope effects are likely to be encountered in the use of isotope techniques and what problems are studied with primary and secondary isotope effects. By way of example, the results of studies on E2 reactions, particularly in the Hofmann degradation, are discussed, followed by a discussion of some “analytical isotope effects”. Finally, the problems encountered and the information that can be obtained from isotope effects studies on enzyme reactions, and the advantages and disadvantages of competitive and non-competitive techniques are described. In addition to a survey of isotope effects in dehydrogenase reactions, new isotope effects encountered in the dehydrogenation of T-labeled alcohols are reported.     

Large Isotope Effects in Organometallic Chemistry

The kinetic isotope effect (KIE) is key to understanding reaction mechanisms in many areas of chemistry and chemical biology, including organometallic chemistry. This ratio of rate constants, k_H/k_D, typically falls between 1–7. However, KIEs up to 105 have been reported, and can even be so large that reactivity with deuterium is unobserved. We collect here examples of large KIEs across organometallic chemistry, in catalytic and stoichiometric reactions, along with their mechanistic interpretations. Large KIEs occur in proton transfer reactions such as protonation of organometallic complexes and clusters, protonolysis of metal–carbon bonds, and dihydrogen reactivity. C−H activation reactions with large KIEs occur with late and early transition metals, photogenerated intermediates, and abstraction by metal-oxo complexes. We categorize the mechanistic interpretations of large KIEs into the following three types: (a) proton tunneling, (b) compound effects from multiple steps, and (c) semi-classical effects on a single step. This comprehensive collection of large KIEs in organometallics provides context for future mechanistic interpretation.     

Atom Tunneling in Chemistry

Quantum mechanical tunneling of atoms is increasingly found to play an important role in many chemical transformations. Experimentally, atom tunneling can be indirectly detected by temperature‐independent rate constants at low temperature or by enhanced kinetic isotope effects. In contrast, the influence of tunneling on the reaction rates can be monitored directly through computational investigations. The tunnel effect, for example, changes reaction paths and branching ratios, enables chemical reactions in an astrochemical environment that would be impossible by thermal transition, and influences biochemical processes.     

Probing Substrate Diffusion in Interstitial MOF Chemistry with Kinetic Isotope Effects

Metal–organic frameworks (MOFs) have garnered substantial interest as platforms for site‐isolated catalysis. Efficient diffusion of small‐molecule substrates to interstitial lattice‐confined catalyst sites is critical to leveraging unique opportunities of these materials as catalysts. Understanding the rates of substrate diffusion in MOFs is challenging, and few in situ chemical tools are available to evaluate substrate diffusion during interstitial MOF chemistry. Herein, we demonstrate nitrogen atom transfer (NAT) from a lattice‐confined Ru₂ nitride to toluene to generate benzylamine. We use the comparison of the intramolecular deuterium kinetic isotope effect (KIE), determined for amination of a partially deuterated substrate, with the intermolecular KIE, determined by competitive amination of a mixture of perdeuterated and undeuterated substrates, to establish the relative rates of substrate diffusion and interstitial chemistry. We anticipate that the developed KIE‐based experiments will contribute to the development of porous materials for group‐transfer catalysis.     

Exploiting Synergistic Effects in Organozinc Chemistry for Direct Stereoselective C‐Glycosylation Reactions at Room Temperature

Pairing a range of bis(aryl) zinc reagents ZnAr₂ with the stronger Lewis acidic [(ZnAr^F₂)] (Ar^F=C₆F₅), enables highly stereoselective cross‐coupling between glycosyl bromides and ZnAr₂ without the use of a transition metal. Reactions occur at room temperature with excellent levels of stereoselectivity, where ZnAr^F₂ acts as a non‐coupling partner although its presence is crucial for the execution of the C(sp²)–C(sp³) bond formation process. Mechanistic studies have uncovered a unique synergistic partnership between the two zinc reagents, which circumvents the need for transition‐metal catalysis or forcing reaction conditions. Key to the success of the coupling is the avoidance of solvents that act as Lewis bases versus diarylzinc compounds (e.g. THF).     

Polar Effects in Organic Reactions

Attempts to gauge the effect of polar substituents on organic reaction rates by means of “inductive substituent constants” are based on the assumption that these effects are independent of the type of reaction observed. The measured rate constants of nucleophilic substitution reactions show, however, that this assumption is only partly justified even for saturated molecules. It is invalid if the substituent and the reaction center are an electron donor and an electron acceptor, respectively, which are hyperconjugated by way of σ-bonds. In extreme cases the resulting polarization can lead to heterolytic fragmentation.     

Environmental Coordination Chemistry: Binary Systems Comprising Some Bivalent Cations and Monocarboxylates in Aqueous Solution. Ionic Medium Effects on Equilibrium Constants

Abstract

The molar single activity coefficients associated with propionate ion (Pr) have been determined at 25°C and ionic strengths comprised between 0.300 and 3.00 M, adjusted with NaClO₄, as background electrolyte. The investigation was carried out potentiometrically by using a second class Hg/Hg₂Pr₂ electrode. It was found that the dependence of propionate activity coefficients as a function of ionic strength (I) can be assessed through the following empirical equation: log y_pr = –0.185 J^3/2 + 0.104 I². Next, simple equations relating stoichiometric protonation constants of several monocarboxylates and formation constants associated with 1:1 complexes involving some bivalent cations and selected monocarboxylates, in aqueous solution, at 25°C, as a function of ionic strength were derived, allowing the interconversion of parameters from one ionic strength to another, up to I = 3.00 M. In addition, thermodynamic formation constants as well as parameters associated with activity coefficients of the complex species in the equilibria are estimated. The body of results shows that the proposed calculation procedure is very consistent with critically selected experimental data.     

Steric Interactions in Organic Chemistry: Spatial Requirements of Substituents

From the very extensive factual material available on steric interactions in organic chemistry, the present paper reviews the investigations that provide information about the “size” (“spatial requirement”) of the substituents. After an introductory section on the results obtained with the aid of spectroscopic data and by analysis of chemical reactions, attention is turned to conformational processes, including hindered rotation in ethanes, in the biphenyl system, in butadienes, multiply substituted arenes, molecular propellers, and triptycenes. The main emphasis is placed on the explanation of sterically hindered ring inversions in bridged arenes, a class of compounds particularly suitable for the study of steric interactions. The results obtained by variation of the parameters in this system are also discussed with respect to the spatial requirements of organic substituents.     

相对论效应在结构化学中的作用

相对论发表已100周年,但是相对论效应在化学中的重要性却是在近20年来才被人们所了解。这是由于这些年计算化学蓬勃地发展,揭示出来许多有关化学中电子的、结构的和化学键的新信息;另外,无机化学,特别是含有重元素的无机化学的发展,也揭示出许多新的规律和实验测定出来的数据。这些只能在考虑到相对论效应后,才能合理地、完整地加以解释和描述[1~5]。有关相对论效应在量子化学和光谱性质中作用的进展。可参看有关文献[6~9]。本文主要介绍相对论效应在结构化学中的作用,并以此纪念相对论发表100周年。1相对论效应简介相对论推得物质质量m的表…