意想不到的微小的正氧替代剂对基碳酸盐的稳定性的作用
M Fujio1, J R Keeffe, R A More O'Ferrall
1Institute for Materials Chemistry and Engineering, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 82, Japan.
Journal of the American Chemical Society
|August 12, 2004
概括
该研究量化了基醇电离的平衡常数,揭示了氧取代剂对碳酸稳定性有重大影响. 循环系统中的 conformational 效应影响结合效率,影响反应结果.
科学领域:
- 物理有机化学 有机化学
- 反应动力学反应动力学
- 碳化物化学 碳化物化学
背景情况:
- 研究基醇的电离,以形成碳酸.
- 检查了整形替代剂 (基,氧,硫) 对碳酸稳定性的影响.
- 由于在循环系统中观察到氧/硫结合的微小或反向动力效应.
研究的目的:
- 报告替代醇的电离的平衡常数.
- 阐明正氧替代剂对碳酸稳定性的影响.
- 了解电子效应和形状约束之间的相互作用.
主要方法:
- 酸催化酒精电离的测量速率常数 (kH).
- 使用亚时钟法确定与水 (kH2O) 的碳酸反应.
- 通过结合动力数据来计算平衡常数 (pKR).
主要成果:
- 报道了各种替代基碳酸盐的pKR值,范围从-9.3到-13.8.
- 与小的动力效应相比,在indanol中发现了250倍的正氧平衡效应.
- 观察到四醇中正氧的平衡效应小得多 (1.6倍),与其动力效应形成鲜明对比.
结论:
- 对基碳酸的正氧结合的效率是形状敏感的,受环应变的影响.
- 在indanol中,正氧的动力效应来自在过渡状态下的共振和感应效应的平衡.
- 替代物的平衡和动力效应可能会显著不同,特别是在受限制的结构系统中.
相关概念视频
Buffers
A solution containing appreciable amounts of a weak conjugate acid-base pair is called a buffer solution, or a buffer. Buffer solutions resist a change in pH when small amounts of a strong acid or a strong base are added. A solution of acetic acid and sodium acetate is an example of a buffer that consists of a weak acid and its salt: CH3COOH (aq) + CH3COONa (aq). An example of a buffer that consists of a weak base and its salt is a solution of ammonia and ammonium chloride: NH3 (aq) + NH4Cl...
Calculating pH Changes in a Buffer Solution
A buffer can prevent a sudden drop or increase in the pH of a solution after the addition of a strong acid or base up to its buffering capacity; however, such addition of a strong acid or base does result in the slight pH change of the solution. The small pH change can be calculated by determining the resulting change in the concentration of buffer components, i.e., a weak acid and its conjugate base or vice versa. The concentrations obtained using these stoichiometric calculations can be used...
Buffer Effectiveness
Buffer solutions do not have an unlimited capacity to keep the pH relatively constant . Instead, the ability of a buffer solution to resist changes in pH relies on the presence of appreciable amounts of its conjugate weak acid-base pair. When enough strong acid or base is added to substantially lower the concentration of either member of the buffer pair, the buffering action within the solution is compromised.
The buffer capacity is the amount of acid or base that can be added to a given volume...
The buffer capacity is the amount of acid or base that can be added to a given volume...
Bicarbonate-Carbonic Acid Buffer
The carbonic acid-bicarbonate buffer system is critical for maintaining the body's pH balance. It operates on the equilibrium:
Respiratory Regulation of Acid-Base Balance
Respiratory compensation is a vital physiological process that stabilizes blood plasma pH by regulating the partial pressure of carbon dioxide (PCO2), a key determinant of pH levels. Most carbon dioxide in the blood dissolves and converts into carbonic acid (H2CO3). It dissociates into hydrogen ions (H+) and bicarbonate ions (HCO3⁻). There is also an inverse relationship between PCO2 and pH.
When carbon dioxide levels increase in the blood, more H+ and HCO3⁻ are produced, leading to a...
When carbon dioxide levels increase in the blood, more H+ and HCO3⁻ are produced, leading to a...
Buffers: Overview
Buffers play a crucial role in stabilizing the pH of a solution by mitigating the effects of small amounts of added acid or base. They consist of a weak acid and its conjugate base or a weak base and its conjugate acid. A solution of acetic acid and sodium acetate is an example of a buffer that consists of a weak acid and its salt: CH3COOH (aq) + CH3COONa (aq). An example of a buffer that consists of a weak base and its salt is a solution of ammonia and ammonium chloride: NH3 (aq) + NH4Cl (aq).


