色谱柱长估算问题的一题多解分析

习题教学是学生实现知识向能力转化的重要环节，一题多解有利于所学知识的融会贯通，有利于培养和强化学生的发散性思维。本文介绍了一道色谱柱长估算题的5种解题方法，讨论了常见解题错误，并由此来深化理解色谱基础理论知识。     

科学解题与培养能力

问题的提出根据近几年全国高等学校统一招生化学试卷分析和教师反映,学生的化学知识有以下缺陷： 有的学生,“双基”学得不错,但缺乏综合提高的能力; 有的学生说：“单问这个概念,还会答,一综合起来就糊涂”; 不少学生,大量地解难题,陷入“题悔”,做了一题,只会一题,过后又把它忘了; 相当普遍的学生,只死肯知识不去解题,或只死套公式、用死方法去解答简单的题; 多数学生,对实验现象模糊,叙述实验现象语无伦次,缺乏最基本的表达能力;……出现这些现象的原因很多,没有认清解题在教学中的地位,是其原因之一。     

中学化学知识“提取困难”成因及教学对策研究

化学知识"提取困难"归纳为4种表现:不能及时提取相关知识;不能独立提取相关知识;不能准确提取相关知识;不能全面提取相关知识。化学知识"提取困难"的原因有:知识内容不熟悉;知识意义不明确;知识连接不清晰;知识网络不完善;知识情境不真实;知识负迁移效应等。克服知识"提取困难"对策主要包括:优化教学方式,注重学生的知识"输出";营造真实环境,促进知识迁移;围绕核心概念,建立知识连接;理清知识关系,完善知识网络;精心设计问题,加强自我监控;辨清新旧联系,克服定式干扰等。     

有机框图题的解法

有机框图题是历年高考的热点题型,具有试题情景新、知识覆盖广、设问角度活等特点。它既可全面考查学生的有机基础知识,还可综合考查学生运用知识分析问题解决问题的能力。要想回答好这类题,学生必须具备扎实的有机化学知识,同时还要有敏捷地接受、分析和评价信息的能力;以及将已有知识与题中信息灵活地结合起来的能力。如何才能快速准确的突破此类题型。     

无机化合物性质实验的考查题

在我系七七级无机化学实验的期终考查中,我们设计过这样的选作题：给一包或几包未知物质的样品,让学生用样品做几个指定的实验,并要求根据实验现象,运用所学的知识来判断样品是什么物质。结果学生很感兴趣,在七九级的实验期终考查中,学生反映也很好。这类实验题能让学生通过鲜明生动的实验现象,运用课堂上所学的知识来解决实际问题。     

1987年全国高二学生化学竞赛题和参考答案

1987年11月,在全国范围内举行了一次高二学生化学竞赛。本刊特公布这份赛题,一是作为历史资料;二是为引起各界的注视和研讨,推动化学竞赛的发展。据有关人士说：这种全国高二学生化学竞赛,今后要年年搞,一年一度;赛题的知识水平,就其基本内容,不超过高二化学的大纲和进度;但赛题要求参赛音有较高的智力水平。简言之,竞赛是智力的竞赛,不是知识的竞赛。或者说,竞赛对参赛者的知识要求是一般的,普遍可及的,而对参赛者的智力要求是特殊的,但也不是高不可攀的。诚然,不能说下面公布的这份赛题已充分体现了上面的命题原则,但它是努力地去体现这一原则的。以第11题为例。解此题所需的化学知识并不超过中学化学的教学水平：①浓硫酸有吸水性;②浓盐酸有挥发性;③若将浓盐酸滴入浓硫酸,必将出现两个相反的热效应：一方面,浓硫酸与水反应将放热;另一方面,氯化氢挥发将吸热,这跟将纯水滴入浓硫酸的热效应将有差别;④此题所列的其他试剂无一可发生学生已学过的氧化还原反应并放出某种气体;⑤所谓“纯净的”气体自然包含着连水蒸气也不应作为杂质;⑥氯化氢极易溶于水,为制得纯 HCl 气体绝不应用水溶液去洗涤它;……如果说,这些知识超出了学生的认识范围,绝不是各个知识点本身而是它们的综合。而综合知识,从本质上讲,是智力,不是知识本身。尽管该题的干燥氯化氢气体的制法本身正是实验室少量 HCl 气体制法的常规方法,但中学化学,甚至大学化学里都未提及,这或许是教材有些问题,但似乎也不必要求凡是有用的教材里都必须讲到。出题者或许正是考虑到应当取大家不熟悉的命题来作为赛题对所有参赛者才是公平合理的。参赛者及其指导者们不应当去补知识,若是以这种想法来准备竞赛,恐怕是补不完的。重要的是将已学的知识、概念、原理综合起来,运用于新的未知的场合,以得出正确的结论。     

焦虑对高中生化学问题解决的影响研究

通过问卷调查、口语报告和访谈等手段,探查了焦虑对高中生化学问题解决的影响。结果表明：焦虑程度过高会使问题解决者在问题表征阶段提取题给信息不全面,难以辨别干扰信息;在选择策略阶段不能灵活敏捷地提取已有知识进行类比、迁移,进而不能选择恰当的解题策略;在执行策略和评价解答阶段,过多担心结果的正确性会导致低效地进行评价监控。     

无机化学中的一题多解

无机化学计算中采取一题多解可开拓学生的思维,加深对化学基本原理的理解和掌握,有利于巩固和提高所学知识,并加以灵活运用,做到触类旁通。文章以无机化学教学中化学平衡、电极电势2类问题的计算给予说明。     

基于项目式学习的高三化学实验和工艺流程专题复习*——以“海带中碘的提取”为例

以“海带中碘的提取”为例,提供文献让学生课前阅读,完成“海带中碘的提取”流程设计,并进行成果交流。在此基础上,进行方案实施,并进行总结评价。研究结果认为,将知识与实践结合,能够激发学生探究热情;将自主文献研究、方案设计、实验验证结合,可以培养学生的科学探究和创新能力;应该注重教-学-评一致性;需要进一步提高教师的实验实际操作能力和知识引导能力。     

国际化学竞赛中双原子体系问题的化简思想

在近几年的国际化学竞赛中,出现了涉及量子化学基础的赛题,特别是双原子体系这样比较容易被中学生理解的知识点颇受青睐.由于完整地学习双原子体系需要高等数学和大学物理的知识作支撑;那么,如何简明地向高中生讲解相关知识,传授有关赛题的解题方法,便成了值得关注的问题.通过1道IChO预备题和1道IChO原题的剖析,给出了化简分析双原子体系的思路,并指出物理意义上的类比迁移是使高中生理解复杂知识的一种有效途径.     

A carbanion induced synthesis of highly congested pyrazole and imidazole containing heterocycles

An efficient approach to the synthesis of highly congested di, penta and hexacyclic pyrazoles as well as imidazole fragment containing novel heterocyclic molecule has been developed through a carbanion induced transformation of suitably functionalized 2H-pyran-2-ones, benzo[h]chromene and thiochromeno[4,3-b]pyrans. Due to the presence of fluorescence, we report their prime application metal sensor as off/on switching in ferric ions.     

α-Amino acid derived enaminones and their application in the synthesis of N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates and other heterocycles

A new and simple synthesis of novel N-protected methyl 5-substituted-4-hydroxypyrrole-3-carboxylates, which exist in equilibrium with their 4-oxo tautomers, has been developed in two steps starting from N-protected α-amino acids. The key intermediates are enaminones, which can also be isolated, characterized, and used for the construction of other functionalized heterocycles, before they spontaneously decompose to pyrrole products. 4-Hydroxypyrroles are prone to partial aerial oxidation but can be efficiently alkylated or reduced to stable polysubstituted pyrrolidine derivatives.     

Specific intramolecular aromatic CH insertion of diazosulfonamides

The chemoselectivity in the intramolecular CH insertion of various diazosulfonamides has been experimentally studied. The results reveal that the aliphatic 1,4-, 1,5-, or 1,6-C(sp³)?H insertions of diazosulfonamides are not accessible, while the aromatic 1,5-C(sp²)?H insertion can be realized specifically by adjusting the diazo-adjacent group. In addition, the general chemoselectivities in the intramolecular CH insertions of diazosulfonyl compounds are summarized. Generally, diazosulfones undergo both aromatic 1,5-C(sp²)?H and aliphatic 1,5- and 1,6-C(sp³)?H insertions, while diazosulfonates undergo aliphatic 1,5- and 1,6-C(sp³)?H insertions. However, diazosulfonamides only undergo aromatic 1,5-C(sp²)?H insertion.     

N-Heterocyclic carbene-palladacyclic complexes: synthesis,characterization and their applications in the C-N coupling and α-arylation of ketones using aryl chlorides

N-Heterocyclic carbene-palladacyclic complexes 3 were successfully achieved in a one-pot procedure under mild conditions. The structure of 3a was unambiguously confirmed by X-ray single crystal diffraction and it was an active catalyst in the Buchwald-Hartwig amination and α-arylation of ketones even at very low catalyst loadings (0.01?mol%).     

Selective synthesis of 4,5-dihydroimidazo- and imidazo[1,5-a]quinoxalines via modified Pictet–Spengler reaction

An efficient tandem approach for the selective synthesis of 4,5-dihydroimidazo[1,5-a]quinoxalines 6a–g and imidazo[1,5-a]quinoxalines 7a–h by the reaction of 2-imidazolyl anilines 4a–c with aryl aldehydes 5a–k under mild reaction conditions is described. Introduction of electron releasing alkyl groups in substrates 4a–b was found to be instrumental for the success of the reaction.     

Understanding the Diels-Alder reactivity of 1,2-azaborine analogues

The Diels-Alder reactivity of 1,2-heteroborines (H₄C₄B(H)X, X?=?NH, PH, AsH; O, S, Se) has been computationally explored by means of Density Functional Theory (DFT) calculations. The influence of the HB?=?X fragment on the reactivity of the system has been quantitatively analyzed in detail by means of the so-called Activation Strain Model (ASM) of reactivity. It is found that the interaction between these species and the dienophile is significantly stronger than that computed for their all-carbon isoelectronic counterpart, benzene. In addition, the strain energy plays a key role in the observed reactivity trends. The role of the aromaticity strength of these heteroarenes on the reactivity is also assessed.     

Synthesis of N-substituted carbazolones from α-iodo enaminones via Pd(0)-catalyzed intramolecular coupling under microwave irradiation

A variety of N-aryl and N-alkyl carbazolones were conveniently achieved in good to high yields via Pd₂(dba)₃-mediated intramolecular coupling of N-substituted α-iodo enaminones under microwave irradiation. The Pd(0)-catalyzed cyclization was found to proceed favorably with the more electron-deficient phenyl ring during the reactions involving unsymmetrical N,N-diaryl α-iodo enaminones. This unique property enables the construction of carbazolone skeleton containing nitro substituted benzenoid ring.     

Iodine-mediated oxidative Pictet-Spengler reaction using terminal alkyne as the 2-oxoaldehyde surrogate for the synthesis of 1-aroyl-β-carbolines and fused-nitrogen heterocycles

An efficient iodine-mediated oxidative Pictet-Spengler reaction in dimethyl sulphoxide (DMSO) using terminal alkynes as the 2-oxoaldehyde surrogate for the synthesis of aryl (9H-pyrido[3,4-b]indol-1-yl)methanones is described. The scope of the protocol includes the total synthesis of Fascaplysin, Eudistomins Y₁ and Y₂. The methodology is extended for preparing pyrrolo[1,2-a]-quinoxaline and indolo[1,5-a]quinoxaline derivatives. The utility of 1-aroyl-β-carbolines was demonstrated by performing palladium-catalyzed β-carboline directed ortho-C(sp2)-H functionalization of the phenyl ring with thiomethyl (SMe) group using DMSO as source and for accessing 4-aryl-canthin-6-ones.     

Facile synthesis of bicyclic 1-arylpyrazol-5-ones

In this Letter, we described a facile method for constructing fused bicyclic 1-arylpyrazol-5-one ring system. We employed various methylene-containing carboxylic acids as the substrates and proved that the pyrazolone ring closure requires activated methylene group in intermediate II. Accordingly, a series of structurally diversified, fused bicyclic 1-arylpyrazol-5-ones was prepared in moderate to high yields using the requisite substrates.     

Synthesis of substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles by intramolecular nitrilimine cycloaddition

Both substituted 2,4,5,6-tetrahydrocyclopenta[c]pyrazoles and 2,4,5,6-tetrahydropyrrolo[3,4-c]pyrazoles have been synthesized by the 3+2 intramolecular dipolar cycloaddition of nitrilimines to alkynes. This cyclization has been extended to more versatile 3-bromo derivatives by the use of alkynylbromides as dipolarophiles.