电极电势在平衡体系中的妙用

电极电势是电化学的基本概念,然而很多学生对此概念的理解较为肤浅以至于不能灵活应用。以平衡态电极电势在几类物理化学平衡体系的应用为例,详证如何巧妙地应用该原理化难为易,解决问题,帮助学生提升对概念的理解及应用能力。     

深入原电池原理本质促进学生观念和能力的发展

在调查分析高三学生对原电池原理的理解及应用状况的基础上,论述了从电极电势及平衡移动的角度理解原电池中产生持续电流的原因,有助于学生能量观的建构及学生能力的发展。以高三原电池复习教学为例,阐述了促进学生理解学科知识本质的探究活动的设计。     

数轴在电化学教学中的妙用

电池符号、电极电势和电极极化是物理化学电化学教学中三个非常重要的知识点。本文以极易记忆的“数轴”为模型,阐述了数轴在这三个方面教学中的妙用。基于实例详细说明了如何以数轴模型理解记忆电池符号的规定、电极电势的大小及应用和电极极化的概念及应用。     

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。     

揭示内在规律 培养学生能力——对元素化学教学的探索

本文在归纳周期系中元素氧化态递变规律及运用电极电势、电势图阐明无机反应规律等方面作了一些探索,以在无机化学教学中使学生在学习元素化学性质的同时培养理解、分析归纳的能力。     

AgCl/Ag标准电极电势的教学难点突破

对于有难溶物参与的电极反应,其标准电极电势的计算是教学中的一个难点。根据大一学生认知特点,通过转换视角,复习前期知识点,顺利实现计算AgCl/Ag电对标准电极电势的难点突破。     

关于标准氢电极

在电化学教学、生产和科学研究中,电极电势是一个基本的和重要的概念。电极电势的测定在电极过程动力学、腐蚀和电势—pH图等方面都有着广泛的应用。因此,早已有文章就电极电势的有关问题进行过讨论。对于电极电势,一些物理化学教科书中大都是采用国际纯粹与应用化学联合会(IU-     

电极电势和氧化还原反应

以实验为例讨论电极电势和氧化还原反应的关系,总结出如何通过电极电势差判断反应倾向;电极电势与氧化还原反应的速率无关;氧化还原反应和酸碱性的关系以及运用电极电势应关注的问题。     

锂标准电极电势反常现象的热力学讨论

在IA族中,锂的标准电极电势是最负的,但锂的还原性却是同族元素中最弱的,这与利用标准电极电势来判断碱金属的还原性是相互矛盾的.本文利用玻恩-哈伯循环,从热力学角度探讨了锂标准电极电势出现反常现象的原因.     

在298K标准锌汞齐电极的标准电极电势

饱和锌汞齐电极的标准电极电势,一般是指含锌量10％的锌汞齐电极对活度为1的锌离子所产生的电极电势,ε_(Zn~2+)~0+Zn-Hg(Zn10％)=—0.7618±0.0008V。固体金属锌电极的标准电极电势是指金属锌电极对活度为1的锌离子所产生的电极电势ε_(Zn~2+)~0-Zn=0.7618V。     

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%.     

Synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives

Different approaches for the synthesis of 1-benzyloxypyrazin-2(1H)-one derivatives from simple amino acids have been investigated. A library of 33 precursors for the preparation of N-hydroxy pyrazinones was obtained in moderate to good yields.     

A general and convenient synthesis of 4-(tosylmethyl)semicarbazones and their use in amidoalkylation of hydrogen,heteroatom, and carbon nucleophiles

A general synthesis of previously unknown semicarbazone-based α-amidoalkylating reagents, 4-(tosylmethyl)semicarbazones, has been developed. The synthesis involved three-component condensation of semicarbazones of aliphatic or aromatic aldehydes with the same or other aldehydes and p-toluenesulfinic acid. The scope and limitations of this reaction were investigated. The compounds obtained were demonstrated to be an efficient α-(4-semicarbazono)alkylating agents. They were reacted with H- (sodium borohydride), O- (sodium methylate), S- (sodium phenylthiolate), N- (pyrrolidine, sodium succinimide), P- (trialkyl phosphites), and C-nucleophiles (sodium diethyl malonate) to give the corresponding products of the tosyl group substitution, 4-substituted semicarbazones, including analogues of nitrofurazone. Among the prepared compounds tested in vitro for antibacterial and antifungal activity, three nitrofuryl-containing semicarbazones exhibited high biological activities with minimum inhibitory concentration (MIC) values of 8–32 μg/mL.     

Toward new camptothecins. Part 6: Synthesis of crucial ketones and their use in Friedländer reaction

In the context of the preparation of camptothecin and luotonin A analogs, the synthesis of some key keto-precursors and their use in Friedländer condensation are described. This paper also focuses on the stability of these keto intermediates and emphasizes the major differences between indolizinones and pyrroloquinazolinones series. Noteworthy is also the report of some original structures isolated as by-products of some experiments.     

Synthesis of novel chiral bidentate hydroxyalkyl-N-heterocyclic carbene ligands and their application in palladium-catalyzed Mizoroki–Heck couplings and asymmetric addition of diethylzinc to benzaldehyde

A small library of new chiral bidentate hydroxyalkyl-imidazolium salts 1 is conveniently synthesized on multi-gram scale from inexpensive and commercially available chiral pool amino acids. The corresponding carbenes, generated by deprotonation of imidazolium salts 1, in combination with palladium(II) chloride were tested in the Mizoroki–Heck coupling reaction. The most significant results in terms of yields and reactivities were achieved with low catalyst loading. The catalytic activities of these imidazolium salts were also investigated in the asymmetric addition of diethylzinc to benzaldehyde. The use of MgO nanoparticles as an additive in conjunction with these ligands played a crucial role in increasing the efficiency of these reactions.     

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.     

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.     

Microwave-assisted copper-catalyzed stereoselective ring expansion of three-membered heterocycles with α-diazo-β-dicarbonyl compounds

Microwave-assisted copper-catalyzed ring expansions of three-membered heterocycles with α-diazo-β-dicarbonyl compounds were investigated. Thiiranes generated 3-acyl-5,6-dihydro-1,4-oxathiines in the presence of copper sulfate and trans-3-acyl-5,6-dihydro-1,4-oxathiines as stereospecific products for 1,2-disubstituted cis-thiiranes through an intramolecular S_N2 process. Oxiranes gave rise to 2-acyl-5,6-dihydro-1,4-dioxines under the catalysis of copper hexafluoroacetylacetonate and cis-3-acyl-5,6-dihydro-1,4-dioxines as stereospecific products for 1,2-disubstituted cis-oxiranes via an intimate ion-pair mechanism. The current method provides a direct and simple strategy in efficient preparation of 3-acyl-5,6-dihydro-1,4-oxathiines and 2-acyl-5,6-dihydro-1,4-dioxines, important agents in medicinal and agricultural chemistry, from readily available thiiranes and oxiranes, respectively.     

KMnO4-mediated oxidative CN bond cleavage of tertiary amines: Synthesis of amides and sulfonamides

KMnO₄-mediated oxidative CN bond cleavage of tertiary amines producing secondary amine was introduced, which was trapped by electrophiles (acyl chloride and sulfonyl chloride) to form amides and sulfonamides. The reaction could take place at mild condition, tolerating a wide range of function groups and affording products in moderate to excellent yields.