在循环guanidinium离子的水解中是否存在立体电子控制?
1Department of Chemistry, University of California, San Diego, La Jolla, California 92093-0358, USA.
Journal of the American Chemical Society
|July 18, 2001
概括
研究了循环guanidinium盐水解中的立体电子效应. 结果表明环形大小影响单双参与四面体中间裂变,六个环形环形显示弱的反周平加速.
科学领域:
- 有机化学 有机化学
- 反应机制 反应机制
- 立体化学是一种立体化学.
背景情况:
- 四面体中间体是许多有机反应的关键.
- 立体电子效应,特别是单独对参与,可以影响反应路径.
- 关尼盐为研究这些影响提供了一个模型系统.
研究的目的:
- 调查立体电子效应在循环瓜尼尼盐水解中的作用.
- 为了确定反外平面单一对是否控制四面体中间体的裂变.
- 为了比较环形大小对反应结果的影响.
主要方法:
- 合成五,六,和七个成员的循环guanidinium盐.
- 这些盐在基本介质中的水解.
- 使用质子核磁共振 (1H NMR) 光谱分析反应产物.
主要成果:
- 水解产生了循环和非循环尿素产物的混合物.
- 六个成员的环显示出来自反周边平面单一对的轻微加速.
- 五个和七个环没有表现出来自反周平单独对的加速,但显示出来自同步单独对的潜在加速.
结论:
- 通过反环平面单双的立体电子控制在循环guanidinium盐水解中并不普遍运行.
- 戒指大小显著影响了控制四面体中间裂纹的立体电子效应.
- 同时单独的对可能在加速某些环系统的中间分解中发挥作用.
相关概念视频
Electrolyte and Nonelectrolyte Solutions
Substances that undergo either a physical or a chemical change in solution to yield ions that can conduct electricity are called electrolytes. If a substance yields ions in solution, that is, if the compound undergoes 100% dissociation, then the substance is a strong electrolyte. Complete dissociation is indicated by a single forward arrow. For example, water-soluble ionic compounds like sodium chloride dissociate into sodium cations and chloride anions in aqueous solution.
Valence Bond Theory
Coordination compounds and complexes exhibit different colors, geometries, and magnetic behavior, depending on the metal atom/ion and ligands from which they are composed. In an attempt to explain the bonding and structure of coordination complexes, Linus Pauling proposed the valence bond theory, or VBT, using the concepts of hybridization and the overlapping of the atomic orbitals. According to VBT, the central metal atom or ion (Lewis acid) hybridizes to provide empty orbitals of suitable...
Controlled-Potential Coulometry: Electrolytic Methods
Controlled-potential coulometry, also known as potentiostatic coulometry, employs a three-electrode system in which the working electrode's potential is precisely regulated using a potentiostat. Platinum working electrodes are utilized for positive potentials, while mercury pool electrodes are favored for extremely negative potentials. The platinum counter electrode is separated from the analyte using a membrane or salt bridge to avoid interference in the analysis.
The chosen potential ensures...
The chosen potential ensures...
Extraction: Advanced Methods
Metal ions can be separated from one another by complexation with organic ligands–the chelating agent– to form uncharged chelates. Here, the chelating agent must contain hydrophobic groups and behave as a weak acid, losing a proton to bind with the metal. Since most organic ligands used in this process are insoluble or undergo oxidation in the aqueous phase, the chelating agent is initially added to the organic phase and extracted into the aqueous phase. The metal-ligand complex is formed in...
Controlled-Current Coulometry: Overview
Controlled current coulometry, also known as amperostatic coulometry, is a technique used in electrochemical analysis to measure the quantity of a substance through the controlled passage of current. It involves the application of a constant current to an electrochemical cell containing the analyte of interest. As the current flows through the cell, the analyte undergoes a redox reaction at the electrode surface, resulting in a charge transfer. By monitoring the time required for a certain...


