对于脱碳化解的溶剂依赖的过渡状态
D Sicinska1, D G Truhlar, P Paneth
1Institute of Applied Radiation Chemistry, Technical University of Lodz, Zeromskiego 116, 90-924 Lodz, Poland.
Journal of the American Chemical Society
|August 2, 2001
概括
溶剂的选择显著影响4-pyridylacetic酸脱碳化速率和同位素效应. 量子力学建模准确地解释了这些实验溶剂效应.
科学领域:
- 物理化学 物理化学
- 计算化学计算化学
- 化学动力学 化学动力学
背景情况:
- 4-二甲酸的脱碳化表现出显著的溶剂依赖.
- 了解这种溶剂效应对于阐明反应机制至关重要.
研究的目的:
- 解释观察到的速度常数和动态同位素效应的溶剂依赖性,用于4-pyridylacetic酸脱碳化.
- 通过与实验数据进行比较来验证量子力学解法模型.
主要方法:
- 利用了量子力学溶解模型,结合了IV类电荷和半实证原子表面张力.
- 计算了自由能量屏障的溶剂依赖性.
- 计算的 (13) C 和 (18) O 动态同位素效应.
主要成果:
- 该模型成功地重现了速率常数和动态同位素效应的实验溶剂依赖性.
- 过渡状态位置 (C-C键长度) 发现与气相相比,在二氧化中较晚的0.24 Å,在水中较晚的0.37 Å.
- 在过渡状态下,CO2部分的电荷发展在二氧化中比在水中更大 (0.07电子电荷单位).
结论:
- 量子力学溶解模型提供了对实验结果的一致而准确的解释.
- 理论和实验之间的一致性验证了从模型中得出的反应机制的物理图像.
- 溶剂极性在脱碳化过程中显著影响过渡状态结构和电荷分布.
相关概念视频
Energy Diagrams, Transition States, and Intermediates
Free-energy diagrams, or reaction coordinate diagrams, are graphs showing the energy changes that occur during a chemical reaction. The reaction coordinate represented on the horizontal axis shows how far the reaction has progressed structurally. Positions along the x-axis close to the reactants have structures resembling the reactants, while positions close to the products resemble the products. Peaks on the energy diagram represent stable structures with measurable lifetimes, while other...
Sublimation
Sublimation is the direct transformation of a solid to a gaseous state. For instance, at standard pressure and room temperature, solid carbon dioxide sublimes to gaseous carbon dioxide. The phase diagram depicts the conditions required for sublimation. This process occurs at the solid-gas phase boundary and is not observed above the triple point of the substance. The reverse of sublimation is called deposition, where a gaseous substance condenses directly into a solid. Sublimation and...
Ion Exchange
Ion exchange chromatography separates charged molecules from a solution by reversibly exchanging them with mobile, or 'active', ions associated with the oppositely charged stationary phase. This method can be used to separate ions, soften and deionize water, and purify solutions. The polymers comprising the ion-exchange column are high-molecular-weight and chemically stable polymers, crosslinked to be porous and essentially insoluble. They are also functionalized with either acidic or basic...
Transition State Theory
Transition-state theory, also known as activated-complex theory, provides a molecular-level explanation of reaction rates in both gas-phase and solution-phase reactions. It extends earlier kinetic models by considering the formation of a short-lived, high-energy configuration during a reaction.The progress of a chemical reaction can be represented using a reaction profile, which plots potential energy against the reaction coordinate. As two reactant molecules approach one another, their...
Catalysis
Catalysis influences the rate of chemical reactions by providing an alternative reaction pathway with lower activation energy. A catalyst speeds up a reaction, but it is not consumed during the process. The fundamental principle of catalysis is the ability of a catalyst to alter the reaction mechanism, often introducing a more efficient pathway than the uncatalyzed process.In a catalyzed reaction, the catalyst participates directly in the reaction mechanism. It interacts with reactants to form...
Carbon-dioxide Fixation
Carbon dioxide fixation in prokaryotes enables the assimilation of inorganic carbon into organic molecules, supporting biosynthetic pathways, sustaining ecosystems, and contributing to the global carbon cycle. It also has industrial applications in carbon capture and bioproduct synthesis. Autotrophic organisms rely on this process to utilize CO₂ as a carbon source in diverse environments.The Calvin CycleThe Calvin cycle is the most widespread carbon fixation mechanism, primarily used by...


