共查询到20条相似文献,搜索用时 140 毫秒
1.
2.
采用示差扫描量热技术(DSC)对聚乙烯醇(PVA)水溶液反复冰冻过程中的溶剂化效应进行研究.引入水化数的概念来表征溶剂化效应的大小.结果表明不同浓度区间的PVA水溶液其在反复冰冻过程中溶剂化效应显著不同,主要归因于高分子链分子内和分子间缠结程度对溶剂分子"参与"溶剂化的程度和方式的不同.作者把极稀高分子溶液的研究结果拓展到高分子稀溶液或亚浓溶液区间,阐述了高分子溶液中高分子链的物理图像.冷冻次数的增加导致链间缠结增加,部分溶剂则被包裹在由链间缠结点所形成的网圈内成为分子链的一部分.溶液溶剂化程度的变化受到包裹溶剂与高分子链脱溶剂化的综合影响. 相似文献
3.
将溶剂压的概念引入溶液反应的笼效应中,不仅能用来说明溶剂的极性对溶液反应速率的影响,而且还能说明在何种溶剂下溶液反应速率会出现扩散控制和活化控制等动力学现象。 相似文献
4.
现有化学工业过程使用了大量的溶剂。溶剂的使用带来了费时费力和高污染风险的溶剂处理过程,而且因为化学平衡的出现降低了产率。本实验提供了一种使用少量溶剂,而且在反应结束时蒸去溶剂推动反应进行到底的少溶剂固态化学反应实例,对化学过程的绿色化及其观念的推广有重要意义。研究发现,固体氯化铵和六水合氯化钴的2∶1物质的量比混合物在35℃机械搅拌下的反应,在不加水时反应仅停留在表面;加少量水和溶液反应均存在化学平衡;但如果把水蒸干,反应混合物的XRD谱中只有(NH4)2[CoCl4(H2O)2]的衍射峰,基本看不到NH4Cl的。 相似文献
5.
6.
7.
8.
9.
10.
聚谷氨酸苄酯脱保护制备聚L-谷氨酸的正交实验研究 总被引:1,自引:0,他引:1
聚L-谷氨酸苄酯(PBLG)用体积分数为33%的HBr-醋酸溶液脱保护得到聚L-谷氨酸(PLGA). 采用正交实验研究了温度、时间、溶剂及33%HBr-醋酸溶液用量在脱保护过程中对聚L-谷氨酸分子量的影响. 结果表明, 反应温度越高, 时间越长, 溶剂二氯乙酸用量越大, PBLG降解越快, 得到的PLGA分子量越小; 33%HBr-醋酸溶液的影响则相反, 随着33%HBr-醋酸溶液用量的增加, 反应体系酸性减弱, PBLG溶解度降低, 肽键断裂减缓, PLGA分子量也就相对较大. 相似文献
11.
12.
A general and efficient coupling of aryl bromides with diethyl malonate is presented. The reaction provided the α-arylated diethyl malonates in moderate to good yields with a low loading of CuCl2(5%, molar fraction) and 8-hydroxyquinoline(5%, molar fraction). This method has good compatibility for a wide range of aryl bromides. 相似文献
13.
An efficient synthetic protocol for the 1,4-diaryl-1,4-dihydropyridines was developed via the domino four-component reaction of arylamine, acetylenedicarboxylate, aromatic aldehyde and ethyl acetoacetate. The reaction mechanism involves the formation of β-enamino ester and its sequential Michael addition to arylidene acetoacetate. 相似文献
14.
Elbieta Wojaczyska Franz Steppeler Dominika Iwan Marie-Christine Scherrmann Alberto Marra 《Molecules (Basel, Switzerland)》2021,26(23)
Organocatalysis is a very useful tool for the asymmetric synthesis of biologically or pharmacologically active compounds because it avoids the use of noxious metals, which are difficult to eliminate from the target products. Moreover, in many cases, the organocatalysed reactions can be performed in benign solvents and do not require anhydrous conditions. It is well-known that most of the above-mentioned reactions are promoted by a simple aminoacid, l-proline, or, to a lesser extent, by the more complex cinchona alkaloids. However, during the past three decades, other enantiopure natural compounds, the carbohydrates, have been employed as organocatalysts. In the present exhaustive review, the detailed preparation of all the sugar-based organocatalysts as well as their catalytic properties are described. 相似文献
15.
稠杂芳烃的合成是有机化学的重要研究内容之一,对有机光电功能材料和器件研究具有重要意义。C—H键是有机化合物中最广泛存在的化学键。利用C—H键的断裂与重组成键直接构筑稠杂芳烃具有简洁、高效的优势,能够解决传统合成方法在底物制备和产物结构类型方面的局限。本文对近六年来,本课题组在基于导向过渡金属催化(杂)芳环与(杂)芳环之间的C—H/C—H氧化交叉偶联/分子内环化反应策略构筑稠(杂)芳环方面所做的系列工作进行了评述,重点讨论了有关反应的特点、优势和催化机理,并对该策略在新型有机光电材料开发中的应用进行了阐述。最后,对该策略目前存在的问题进行了总结,并展望了其发展前景。 相似文献
16.
M. M. Vartanyan O. L. Eliseev Kh. R. Skov R. A. Karakhanov 《Russian Chemical Bulletin》1997,46(6):1178-1179
Acetonylmalonaldehyde (1) was obtained for the first time by hydrolysis of 2,5-dimethoxy-5-methyltetrahydrofuran-3-carbaldehyde. The interaction of1 with 3-amino-5-methylpyrazole, 3-amino-1,2,4-triazole, 2-aminobenzimidazole, and 5-aminotetrazole results in the formation
of functionally substituted azolopyrimidines.
Deceased.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1226–1228, June, 1997. 相似文献
17.
在过渡金属催化的交叉偶联反应中,有机硅、锡化合物作为偶联亲核试剂已经广为人知,然而同族的锗元素研究却相对较少。锗亲核试剂的偶联反应最初只是简单地证明了锗作为一种"偶联元素"的可行性,但逐步发现的优异性质使得锗试剂已经受到越来越多的关注。本文从锗试剂的结构分类出发,介绍这些锗片段引入有机体系的方法及相应锗试剂的交叉偶联反应。 相似文献
18.
19.
Electrolysis is a potential candidate for a quick method of wastewater cleansing. However, it is necessary to know what compounds might be formed from bioorganic matter. We want to know if there are toxic intermediates and if it is possible to influence the product formation by the variation in initial conditions. In the present study, we use Car–Parrinello molecular dynamics to simulate the fastest reaction steps under such circumstances. We investigate the behavior of amino acids and peptides under anodic conditions. Such highly reactive situations lead to chemical reactions within picoseconds, and we can model the reaction mechanisms in full detail. The role of the electric current is to discharge charged species and, hence, to produce radicals from ions. This leads to ultra-fast radical reactions in a bulk environment, which can also be seen as redox reactions as the oxidation states change. In the case of amino acids, the educts can be zwitterionic, so we also observe complex acid–base chemistry. Hence, we obtain the full spectrum of condensed-phase chemistry. 相似文献
20.
利用量子化学从头算和密度泛函理论(DFT)对SiN和ClO反应机理进行了理论研究.在B3LYP/6-311 G(d,p)水平上优化得到了反应势能面上各驻点的几何构型;通过频率分析和内禀反应坐标(IRC)计算对过渡态与反应物和产物的连接关系进行确认.在CCSD(T)/cc-pVTZ水平上对各物种的能量进行校正,得到了反应势能面.计算结果表明:该反应体系存在单态和三态势能面,其中单态势能面上反应通道(1)和(2)是主反应通道,P4为主产物. 相似文献