共查询到20条相似文献,搜索用时 78 毫秒
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将化学宏观现象进行形象、直观与动态的微观表征,能激发学生的学习兴趣,协助学生理解化学原理与规律。在几种不同形式的微观表征方法中,微观表征图能有效地消除相异构想,是建构化学三重表征的突破口,有利于化学三重表征的转化与融合。 相似文献
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以"浓度对硫代硫酸钠与硫酸反应速率的影响"为内容,将"四重表征"化学教学模式与手持技术结合,发挥手持技术数字化实验仪器的优势,从"数据采集"到"数据分析",逐步引导学生收集必要数据探究浓度对该反应速率的影响,并从"四重表征"模式的4个维度深入探究浓度对反应速率的影响,提高学生运用"四重表征"分析问题的能力。 相似文献
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结合高中化学"电解质的电离"中丰富的教学活动,以感知体验化、微观可视化、知识本源化、认识观念化和符号意义化为教学策略,丰富和深化宏观表征和微观表征,实现化学三重表征的高度融合。 相似文献
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梳理了三重表征研究范式下部分化学学习研究成果。基于三重表征,研究者细致考查学生在宏观表征、微观表征和符号表征等单维度化学学习中遇到的困难;结合信息加工模型,解释了化学学习机制,形成对化学学习的动态认识,指出以上研究中尚待完善之处,以期为化学学习的深入研究提供借鉴。 相似文献
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化学三重表征具有内部表征和外部表征两重含义。从外部表征看,化学三重表征是指化学宏观世界、微观世界和符号世界知识的外在呈现形式;从内部表征看,化学三重表征是指这3种水平的知识在个体头脑中的加工和呈现形式。三重表征是一个互有联系的整体,对化学学习具有重要意义。 相似文献
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'Decoking' of a 'coked' zeolite catalyst in a glow discharge in oxygen is investigated. The 'decoking' process involves reactions of atomic oxygen (O atoms) with 'coke' and yields gases such as CO, CO2 as well as other gaseous products that could be easily pumped out.Three different modes of discharge were investigated including a static mode, a flowing-gas mode, and a periodic-purge mode where the oxygen and other gaseous products of the discharge were replaced by fresh O2 gas after short but regular intervals of time. In some cases, additional heating was also used to provide base temperatures of the order of 100 °C to facilitate penetration of oxygen atoms into the inner layers and cages of the zeolite catalyst.This paper presents some results of spectroscopic analytical techniques used to monitor the atomization of oxygen, oxidation of 'coke', and to confirm the process of 'decoking'. More specifically, radiation emission on the 3 s 5S– 3p 5P transitions of O around 777.2–777.5 nm were selected for monitoring the atomization of O2. On the other hand, X-ray photo-electron spectroscopy (XPS) was used to determine the amount of residual carbon and extent of 'decoking'. Furthermore, evolution of CO and CO2 gases as a function of time was systematically monitored in real time. For CO, the 451.1 nm band head belonging to the B1 - A1 bands of the Angstrom system of the CO spectrum was used, while for CO2, the band head at 353.4 nm belonging to the CO2+ spectrum was used. The rates of evolution of CO and CO2 were related to the rate of 'decoking' of the catalyst. It is noted that in the periodic-purge mode, about 63% of the total yield of CO from a given sample of the catalyst appears in the first 3-min exposure to discharge whereas it takes up to 15 min to remove nearly 94% of the removable carbon under our experimental conditions. 相似文献
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A Studer 《Angewandte Chemie (International ed. in English)》2012,51(36):8950-8958
This Minireview highlights recent developments in radical trifluoromethylation reactions. The trifluoromethyl group belongs to the privileged moieties in medicinal chemistry. Many drugs and drug candidates contain a trifluoromethyl substituent. Also in agrochemicals, the CF(3) moiety often appears. The present article addresses the radical trifluoromethylation of alkenes and arenes mainly focussing on recent achievements. However, important earlier work in this field is also covered. 相似文献
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Asakawa M Brancato G Fanti M Leigh DA Shimizu T Slawin AM Wong JK Zerbetto F Zhang S 《Journal of the American Chemical Society》2002,124(12):2939-2950
The hydrogen-bond-directed synthesis, X-ray crystal structures, and optical properties of the first chiral peptide rotaxanes are reported. Collectively these systems provide the first examples of single molecular species where the expression of chirality in the form of a circular dichroism (CD) response can selectively be switched "on" or "off", and its magnitude altered, through controlling the interactions between mechanically interlocked submolecular components. The switching is achievable both thermally and through changes in the nature of the environment. Peptido[2]rotaxanes consisting of an intrinsically achiral benzylic amide macrocycle locked onto various chiral dipeptide (Gly-L-Ala, Gly-L-Leu, Gly-L-Met, Gly-L-Phe, and Gly-L-Pro) threads exhibit strong (10-20k deg cm(2) dmol(-1)) negative induced CD (theta;) values in nonpolar solvents (e.g. CHCl(3)), where the intramolecular hydrogen bonding between thread and macrocycle is maximized. In polar solvents (e.g., MeOH), where the intercomponent hydrogen bonding is weakened, or switched off completely, the elliptical polarization falls close to zero in some cases and can even be switched to large positive values in others. Importantly, the mechanism of generating the switchable CD response in the chiral peptide rotaxanes is also determined: a combination of semiempirical calculations and geometrical modeling using the continuous chirality measure (CCM) shows that the chirality is transmitted from the amino acid asymmetric center on the thread via the macrocycle to the C-terminal stopper of the rotaxane. This understanding could have important implications for other areas where chiral transmission from one chemical entity to another underpins a physical or chemical response, such as the seeding of supertwisted nematic liquid crystalline phases or asymmetric synthesis. 相似文献
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Concentration effects in "single-molecule" spectroscopy 总被引:1,自引:0,他引:1
Gopich IV 《The journal of physical chemistry. B》2008,112(19):6214-6220
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The syntheses of 3β-hydroxy-5β-carda-14, 20:22-dienolide (= «β»-anhydro-), 3β-hydroxy-5β-carda-8:14, 20:22-dienolide (= «α»-anhydro-) and «δ»-anhydro-digitoxigenin (= probably 3β-hydroxy-5β, 14β-carda-8, 20:22-dienolide) by the best ways known to date, have been described. «δ»-Anhydro-digitoxigenin represents the thermodynamically most stable isomer. In this isomer the double bond in position 8 is unaffected by hydrogenation with Pt in acetic acid; with perbenzoic acid an epoxide results from which, on hydrogenation, the double bond can be regenerated in its original position. Analogous reactions are known to occur in the 8:14-epoxides. 相似文献
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In the article, we presented an instructional design of "Particle in One-Dimensional Box Theory" and "HMO Theory" application based on flipped classroom teaching. The students are instructed to use both "Particle in One-Dimensional Box Theory" and "HMO Theory" to solve the electronic structure of olefins and enhance their understanding of quantum mechanics theory via comparison of "Particle in One-Dimensional Box Theory" and "HMO Theory". 相似文献