探究不同银配合物对银镜反应的影响

为探究配体与银形成不同银配合物对银镜反应的影响,以氨水、乙二胺、硫氰化钾和甲胺为配体,通过利用不同银配合物的稳定常数研究不同温度条件下银镜反应的情况,对银镜形成时间和质量做比较。结果表明,在这4种配体中,以乙二胺为配体形成的银配合物稳定常数较高,且碱性较强,室温条件下能快速形成高质量的银镜,利于课堂上开展银镜反应实验演示教学。     

融"有机""无机"知识于一体--讲好"乙醛"

“乙醛”这节课的重点是乙醛的还原性。由于学生脑海中存在的是以往在无机化学中从电子得失和化合价升降来分析氧化还原的概念,现在又陡然转到从得失氢(或得失氧)的角度来看待有机物的氧化还原反应,感到很不适应,有些茫然,特别是感到乙醛的银镜反应的离子方程式难记。因此,讲好乙醛的还原性也就同时成了这节课的“难点”。     

常温下快速银镜反应条件探究

银镜反应作为高中化学教学中醛基的一个重要性质演示实验,在演示时通常需要水浴加热,且形成银镜所需时间较长。在一系列实验探究的基础上,发现在银氨溶液中加入一定量碳酸钠溶液后再加入乙醛,常温下能够在较短时间内生成银镜。该反应操作简单,银镜形成较快。     

2012年高考理综北京卷对银镜反应考查的研究和思考

2012年高考理综北京卷第27题以实验为载体,以银镜反应的条件和试剂改变为研究对象,让学生经历了问题的提出、资料检索、提出假设、设计实验、预测现象、观察实验、分析结果、得到结论、实验收尾处理的实验探究全过程,是北京市高中新课程改革第3年高考全面提高对化学实验和探究能力考查力度的体现。笔者走进实验室,对试题所涉及的实验条件进行研究,对银镜反应及其操作有了更加明确的认识,并对实验题的命制提出了建议。     

Tollens试剂与银镜反应探讨

Tollens 试剂即硝酸银的氨水溶液,是一种比较弱的氧化剂,能与醛发生银镜反应,而不能与酮反应,因此常用于醛和酮的鉴别。目前国内通用的有机化学实验教材中关于 Tollens 试剂的配制多是采用加入氢氧化钠溶液的方法,但是按照此法配制的 Tollens 试剂进行银镜反应,有时实验效果并不理想,除了醛能发生反应以外,酮以及很多其它化合物也呈正性反应,不能用于区别醛和酮。针对这一问题,我们进行了一些实验与探讨,发现加碱的 Tollens 试剂进行空     

银镜反应实验条件优化的研究性学习活动及行为分析

选择银镜反应实验优化条件为研究性学习活动,阐述了活动目标、实施步骤、银镜反应的正交设计、实验过程及结论。利用NVivo 10.0质性分析工具,对上述活动进行质性分析,阐述了研究过程以及利用NVivo 10.0质性分析工具获得的结论。     

乙醛2个特征反应实验应注意的问题

做银镜反应实验常常遇到一些问题,如镜面发暗,不够光亮,不产生银镜等。而乙醛与氢氧化铜反应常遇到产生黄褐色混浊、暗褐色沉淀或红褐色沉淀等问题。针对以上可能出现的现象,提出了这2个实验在试剂配制和操作过程中应注意的问题,从而为教师提高这2个实验成功率提供借鉴与参考。     

究竟应生成什么

对于乙醛与银氨溶液发生银镜反应,现行高中教材均用离子方程式表示为：CH3CH0+2[Ag(NH3)2]++20H-=> CH3C00-+NH4++2Ag↓+3NH3H2O,无可非议。     

不加热不振荡情况下葡萄糖银镜反应的最佳实验条件探究*

对不加热不振荡情况下的葡萄糖银镜反应进行正交实验设计,以硝酸银浓度、氢氧化钠浓度、葡萄糖浓度3个因素为变量,设计成三因素四水平实验,利用SPSS25.0软件对实验结果进行统计学分析,分别得出考虑银镜镜面效果、银镜反应时长和综合考虑2者时的主要影响因素及最佳实验条件,并结合反应机理对影响因素、最佳条件进行进一步分析。     

有机氧化还原反应方程式的一种配平法：代数法

有机氧化还原反应方程式的一种配平法──代数法李致冉（山东大学化学系，济南２５０１００）有的文献［１］和教科书￣［２］曾介绍过配平有机氧化还原方程式的两种方法，即半反应法和氧化数法。本文介绍另一种方法——代数法。它的具体步骤是：第一，写出基本反应式；第...     

HEPT类化合物的QSAR研究

为定量结构／活性相关性研究提取了量子化学参数,拓扑指数Am,分子连接性指数^mxt及疏水性常数,同时应用正交变换和最佳变量子集算法（Leaps-and-Bonds)进行了变量压缩和选择,进而实施了多元回归分析,并由此结果进行了HEPT类化合物（1－[(2-hydroxyethoxy)methyl]-6-(phenylthio)-thymine derivatives)的结构／活性关系的理论解释,进行了人工神经网络法对于该类化合物的活性预测,其结构明显好于多元回归法。     

Effect of the pH of the medium on the chemical shifts in the PMR spectra and on the distribution of the π-electron density

The dependence of the chemical shifts of the ring protons on the pH of the medium for a number of 4-hydroxyquinoline derivatives was studied by means of PMR spectroscopy. The dipolar and uncharged hydroxy forms exist in equilibrium in aqueous solutions. The effect of intramolecular hydrogen bonding on the character of the dependence of the chemical shift on the pH of the medium in the case of 3-piperidinomethyl-4-hydroxyisoquinoline was investigated. The possibility of the separate protonation of the ring nitrogen and the side-chain nitrogen in 3-piperidinomethyl-4-hydroxyisoquinoline was established. The distribution of the -electron density in 4-hydroxyisoquinoline is in good agreement with its chemical behavior.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1546–1549, November, 1971     

Effect of the pH of the medium on the chemical shifts in the PMR spectra and on the distribution of the π-electron density

The dependence of the chemical shift of the ring protons on the pH of the medium for a number of 3-hydroxyquinoline derivatives was studied by PMR spectroscopy. The regions of ionization of the molecules, which correspond to the ranges of acidic, neutral, and alkaline media, were found. In D₂O, 3-hydroxyquinoline is present only in the uncharged hydroxy form. The presence of intramolecular hydrogen bonding in 4-dimethylaminomethyl-3-hydroxyquinoline has a substantial effect on the character of the dependence of the chemical shift on the pH of the medium; the existence of separate protonation of the nitrogen atoms of the ring and the side chain of 4-dimethylaminomethyl-3-hydroxyquinoline was established. The distribution of the -electron density in the 3-hydroxyquinoline molecule is in good agreement with its chemical behavior during electrophilic substitution.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1540–1545, November, 1971.     

液滴荧光传感与计算机联用技术在微量分析中的应用

通过在LS55型荧光-磷光-发光分光光度计上加装液滴产生及调节附件,采用计算机采集与分析处理数据,成功地研制了双通道液滴光化学传感装置.利用葡聚糖凝胶对复合维生素B中不同组分的选择性吸附来达到分离与同时检测的目的,并将其用于复合维生素B药片的分析,取得了满意的结果.     

On the theory underlying the Car-Parrinello method and the role of the fictitious mass parameter

The theory underlying the Car-Parrinello extended-Lagrangian approach to ab initio molecular dynamics (CPMD) is reviewed and reexamined using "heavy" ice as a test system. It is emphasized that the adiabatic decoupling in CPMD is not a decoupling of electronic orbitals from the ions but only a decoupling of a subset of the orbital vibrational modes from the rest of the necessarily coupled system of orbitals and ions. Recent work [J. Chem. Phys. 116, 14 (2002)] has pointed out that, due to the orbital-ion coupling that remains once adiabatic decoupling has been achieved, a large value of the fictitious mass mu can lead to systematic errors in the computed forces in CPMD. These errors are further investigated in the present work with a focus on those parts of these errors that are not corrected simply by rescaling the masses of the ions. It is suggested that any comparison of the efficiencies of Born-Oppenheimer molecular dynamics (BOMD) and CPMD should be performed at a similar level of accuracy. If accuracy is judged according to the average magnitude of the systematic errors in the computed forces, the efficiency of BOMD compares more favorably to that of CPMD than previous comparisons have suggested.     

From the Micro- to the Macro-: Managing the Conservation of the Warship,Vasa

Sweden's famous warship, Vasa, sank on her maiden voyage in August 1628, and remained on the bottom of Stockholm harbour for 333 years. Raised in 1961, she became the first large-scale wooden object to be treated with polyethylene glycol (PEG). In the summer of 2000 a number of acidic salt precipitations were noticed on the surface of the ship and on wooden artefacts in the storerooms. An international research project has been established to look into the causes of this problem and suggest possible re-treatments. Meanwhile projects are underway to monitor movements in the ship, to build a better support system, and to replace the thousands of iron bolts holding the structure together, while a sophisticated new climate system has recently been installed in the museum.