单片酸和单片酸在对环扩张的反应性方面的差异是什么原因的?
John Morrison Galbraith1, Peter P Gaspar, Weston Thatcher Borden
1Department of Chemistry, University of Washington, Box 351700, Seattle, WA 98195-1700, USA.
Journal of the American Chemical Society
|September 26, 2002
概括
酸的环扩张是内热的,与酸不同. 循环转化为双循环中间体对于基基烯来说仅略微更为内热,这揭示了反应途径的关键差异.
科学领域:
- 计算化学是一种计算化学.
- 量子化学是一种量子化学.
- 有机反应机制 有机反应机制
背景情况:
- 基烯和基胺是具有不同的电子结构的反应性中间体.
- 环膨胀反应对于合成新型循环化合物至关重要.
- 了解这些反应的能量,可以为合成策略提供信息.
研究的目的:
- 为了研究 phenylphosphinidene 的环扩张的潜在能量表面.
- 为了比较 phenylphosphinidene 和 phenylnitrene 的反应途径.
- 阐明它们各自的环膨胀机制差异的起源.
主要方法:
- 完成活动空间自相一致场 (CASSCF) 的计算.
- 完成活动空间第二阶扰动理论 (CASPT2) 的计算.
- 计算异极体反应能量以分析能量来源.
主要成果:
- 通过计算,基胺的环扩张到1--1,2,4,6-环乙烯被认为是高度内热的.
- 将基基烯循环转化为双循环中间体的过程仅比基烯的循环转化更为内热.
- 同位体反应能量计算为观察到的能量差异提供了洞察力.
结论:
- 与基烯相比,基基烯表现出明显不同的环扩张特征.
- 循环化步骤对基烯的能量需求比其随后的环扩张要少.
- 计算分析澄清了这些相关中间体之间的机制区别.
相关概念视频
04:01VSEPR Theory and the Effect of Lone Pairs
Effect of Lone Pairs of Electrons on Molecule Geometry
03:05Acid Strength and Molecular Structure
Binary Acids and Bases
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...
02:16Brønsted-Lowry Acids and Bases
In 1923, the Brønsted–Lowry definition of acids and bases was proposed by Johannes Brønsted and Thomas Lowry. According to this theory, a Brønsted acid is defined as a species that donates a proton in a chemical reaction and gets converted to its conjugate base. A Brønsted base is defined as a species that accepts a proton in a chemical reaction and gets converted into its conjugate acid. These transfers of protons are caused by the displacement of electrons in these reactions, which is...
02:34Molecular Structure and Acidity
An acid can be deprotonated to form a conjugate base or an anion. If the produced anion is more stable, then the acid is stronger. On the contrary, if the anion is unstable, then the acid is weaker. Hence, to determine the acidity of the compound, the stability of its conjugate base is studied using various factors.
The size effect explains the change in atomic size on acidity. When comparing the acids formed from elements that belong to the same column in the periodic table, their atomic sizes...
The size effect explains the change in atomic size on acidity. When comparing the acids formed from elements that belong to the same column in the periodic table, their atomic sizes...
01:28Structures of Carboxylic Acid Derivatives
Structure of Carboxylic Acid Derivatives
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
Carboxylic acid derivatives contain an acyl group attached to a heteroatom such as chlorine, oxygen, or nitrogen. The carbonyl carbon and oxygen are both sp2-hybridized with an unhybridized p orbital.
The three sp2 orbitals of the carbonyl carbon form three σ bonds, one each with the carbonyl oxygen, the α carbon, and the heteroatom, whereas the other two sp2 orbitals of the carbonyl oxygen are occupied by the lone pairs. Further, the unhybridized p...
01:31Substituent Effects on Acidity of Carboxylic Acids
The acidity of carboxylic acids is influenced by the nature of the substituents bounded to the functional group. The acid strength is determined by the stability of the carboxylate anion—the conjugate base formed by dissociating the corresponding carboxylic acid.