“阿伏伽德罗常数”学习困境分析与对策探讨

探索"阿伏伽德罗常数"中"规定"表述背后隐藏的玄机:0.012 kg~(12)C中含有多少原子;"阿伏伽德罗常数"为什么选择~(12)C作为基准;"阿伏伽德罗常数"的数值如何确定等。得出启示,教师对于"规定"表述应当利用学生的原有经验,发挥学生的自主性;挖掘科学史资源,揭示知识的修正性;结合实验过程,突出实验的重要意义。     

关于“阿伏伽德罗常数”的历史考量

从基本物理常数这个视角来看阿伏伽德罗常数会更易理解。最早测出阿伏伽德罗常数的人是法国科学家佩兰。阿伏伽德罗常数的测定历史长达百年,至今仍在继续。"阿伏伽德罗常数"与"物质的量""摩尔"概念具有相同的历史源头,但是在不同学科领域发展着,最后又殊途同归。     

学生园地阿伏伽德罗常数与气体常数测定实验的改进

对阿伏伽德罗常数与气体常数测定实验进行了改进:将原实验中测阴极铜片增重改为测阳极铜片的减重;改变电解液的性质,引入EDTA络合铜离子;用相对更环保的锌片代替铜片等。经过反复实验,最终得到了较优化的实验方案。     

基于手持技术的阿伏伽德罗常数测定

借助手持技术通过电镀法和双液原电池法实验测定阿伏伽德罗常数，进而得出一种新的近似测定阿伏伽德罗常数的方法，并作为教材实验的有益补充，帮助学生理解概念，切实感受化学定量实验的魅力。     

阿佛加德罗常数测定实验中胶头滴管的代用

现行六年制重点中学高中《化学》第一册第163页上,用单分子膜法来测定阿佛加德罗常数的学生实验。为减小实验误差,实验中所用的胶头滴管,必须“尖嘴拉得很细”。     

对高考化学试题中部分错误的分析及修改建议

对高考化学试题中出现的小错误,进行了错因分析,并提出了修改建议,其中包括正方形构型的键角,阿伏伽德罗常数的使用,氯化铝的结构,喷泉实验等。     

物质的量和摩尔

叙述了两种物质的量的比率的测量方法。介绍了物质的量的SI单位——摩尔。定义了涉及物质的量的一些量,其中包括摩尔质量、一般的摩尔量、阿伏伽德罗常数、摩尔气体常数及法拉第常数等。对物质的量及其单位摩尔的概念作了有关历史的叙述。     

物质的量和摩尔

叙述了两种物质的量的比率的测量方法。介绍了特的量的ＳＩ单位－摩尔。定义了涉及物质的理的一些量，其中包括摩尔质量、一般的摩尔量、阿伏伽德罗常数、摩尔气体常数及法拉第常数等。对物质的量及其单位摩尔的概念作了有关历史的叙述。     

摩尔新定义和准确测定的阿伏伽德罗常数

针对2019年国际SI单位新标准的实施,依据文献对阿伏伽德罗常数和摩尔物质量原理进行了简短的历史回顾。着重于摩尔新定义的概念和准确测定阿伏伽德罗常数的描述,突出了原子量精密测量技术、纳米量级精密测量技术以及材料制备和表征技术的发展。相对而言,摩尔新定义更能体现科学方法和科学思维同化学知识的关系,将会对无机化学、分析化学、物理化学等课程教学引起巨大的冲击波,并且会波及到每个化学专业本科生。本文内容可为提高本科生的科研思维和科研素质提供借鉴。     

连续重整催化剂铂中心可接近性研究

在AutoChem II 2920化学吸附仪上,探索以环己烷、苯、甲苯、正庚烷和甲基环戊烷为新有机探针分子表征重整催化剂中Pt的可接近度．通过脉冲实验表明,单铂催化剂在合适条件下可以用环己烷、苯和正庚烷表征出全部金属活性中心;双金属催化剂用苯为探针分子在350℃可以表征全部的金属活性中心,用环己烷作为探针分子在100℃或者正庚烷作为探针分子在170℃可以表征双金属催化剂中的非合金Pt．     

二氧化碳和丙烯直接合成甲基丙烯酸的NiPMo/TiO2催化剂的研究

用溶胶-凝胶法以磷钼酸(MPA)的镍盐溶液水解钛酸四丁酯制备了NiPMo/TiO2催化剂.使用ICP、 XRD、 TG-DTA、 IR、 TPD-MS和微反应技术研究了催化剂的化学组成、热稳定性、化学吸附性质和催化反应性能.杂多钼酸盐与TiO2通过O2-在TiO2表面发生了键合.在623 K下,杂多阴离子仍保持原有的Keggin结构.CO2在Lewis酸位Ni(Ⅱ)和Lewis碱位Ni-O-Mo的桥氧协同作用下生成CO2卧式吸附态Ni(Ⅱ)←O-(CO)←(O--Ni).丙烯有多种吸附态在催化剂上吸附.在563 K、 1 MPa和空速1500 h-1的反应条件下,丙烯的摩尔转化率为3.2%,产物MAA选择性为95%.     

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.     

Highly regioselective Buchwald–Hartwig amination at C-2 of 2,4-dichloropyridine enabling a novel approach to 2,4-bisanilinopyridine (BAPyd) libraries

The highly regioselective Buchwald–Hartwig amination at C-2 of the cheap and readily accessible reagent, 2,4-dichloropyridine with a range of anilines and heterocyclic amines is described. This new methodology is robust and provides a facile access to 4-chloro-N-phenylpyridin-2-amines on 0.25 mol scale. These intermediates undergo a further Buchwald–Hartwig amination at higher temperature to enable rapid exploration of the chemical space at C-4 and to provide a library of 2,4-bisaminopyridines.     

Sulfur-directed metal-free and regiospecific methyl C(sp3)–H imidation of thioanisoles

Regiospecific and direct imidation of the methyl C(sp³)–H bond of thioanisoles is realized under mild and metal-free conditions with N-fluorobis(benzenesulfonyl)imide as an oxidant and nitrogen source. Proposed mechanism suggests that thionium ion intermediates and a Pummerer-type reaction are involved. The imidation has advantages such as high step-economy, excellent functionality tolerance, and regiospecificity, giving structurally diverse imidation products.     

Selective syntheses of 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones via temperature-dependent Rh(II)-carbenoid-mediated 2H-azirine-ring expansion

The Rh(II)-catalyzed reaction of 2-carbonyl-substituted 2H-azirines with ethyl 2-cyano-2-diazoacetate or 2-diazo-3,3,3-trifluoropropionate provides an easy access to 2H-1,3-oxazines and 1H-pyrrol-3(2H)-ones. These compounds can be selectively prepared from the same starting material using temperature as the only varied parameter. The 2-azabuta-1,3-diene intermediate, a common precursor for both heterocyclic products, isomerizes into 2H-1,3-oxazine under kinetic control, while 1H-pyrrol-3(2H)-one is the sole product of the reaction at elevated temperatures. According to DFT-calculations a one-atom oxazine ring contraction involving ring-opening to a 2-azabuta-1,3-diene intermediate, followed by a 1,5- and 1,2-prototropic shift leads to the consecutive formation of imidoylketene and azomethine ylide, which then further undergo cyclization to the pyrrole derivative.     

Copper catalyzed/mediated synthetic methodology for ebselen and related isoselenazolones

Scope of the copper catalyzed/mediated selenium-nitrogen coupling reaction has been studied for the synthesis of isoselenazolones. It is noticed that the 2-chloro, 2-bromo-, and 2-iodo-aryl amides substrates can be exploited in the selenium-nitrogen coupling reaction by employing 25-100 mol % of CuI/1,10-phenanthroline (L) and potassium carbonate as a base in DMF. Furthermore, electron rich 2-chloro-arylamides also underwent selenium-nitrogen coupling reaction to give biologically important selenium-nitrogen heterocycles. Also, copper-catalyzed selenium-nitrogen coupling reaction has been meticulously applied for the synthesis of diaryl diselenides having methoxy, amine, and amide functionality from respective aryl iodides in the presence of stoichiometric amount of succinimide as an external Se-N coupling partner.     

Knoevenagel condensation catalyzed by novel Nmm-based ionic liquids in water

A series of novel N-methyl morpholine (Nmm) based ionic liquids with 1,2-propanediol group were synthesized and used as catalysts for Knoevenagel condensation at room temperature in water. Under the effect of the catalyst, various aldehydes or aliphatic ketones could react with a wide range of activated methylene compounds well, including malononitrile, alkyl cyanoacetate, cyanoacetamide, β-diketone, barbituric acid, 2-arylacetonitrile and thiazolidinedione. Furthermore, most of the products could be separated just by filtrating and washing with water. Additionally, the catalyst is recyclable and applicable for the large-scale synthesis.     

Construction of polyheterocyclic spirotetrahydrothiophene derivatives via sulfa-Michael/aldol cascade reaction

A series of polyheterocyclic spirotetrahydrothiophene derivatives were obtained in moderate to excellent yields via a catalyst-free sulfa-Michael/aldol cascade reaction of chalcones 1 and commercially available 1,4-dithiane-2,5-diol 2 under mild conditions. We also present the first asymmetric sulfa-Michael/aldol cascade reaction of chalcones 1 and commercially available 1,4-dithiane-2,5-diol 2 with moderate to good enantioselectivities catalyzed by readily available chiral phase-transfer catalysts (PTCs).     

Suzuki-Miyaura reactions of the soluble guanylate cyclase inhibitor NS2028: a non-product specific route to C-8 substituted analogues

Both soluble guanylate cyclase (sGC) inhibitors ODQ 1 and NS2028 2 are synthesized via improved protocols. In the former case treating 3,4-dihydroquinoxalin-2(1H)-one oxime 8, which can be prepared in two steps from 1,2-benzenediamine, with 1,1′-carbonyldiimidazole (CDI) gives the dihydro-ODQ 10 that in the presence of KMnO₄ oxidises to give ODQ 1 in an overall yield of 46% starting from 1,2-benzenediamine. In the latter case, the synthesis affords NS2028 2 from 2-amino-4-bromophenol 3 in three steps with an overall yield of 85% and avoids the need for chromatography. Furthermore, Suzuki-Miyaura reaction conditions are described that enable the preparation of 8-aryl and 8-heteroaryl derivatives of NS2028 directly from NS2028 2. Finally, demethylation of the 8-(methoxyphenyl) substituted analogues afforded the 8-(hydroxyphenyl) derivatives 40-42. All new products are fully characterised.