一种热力学方法来分析相对电容性和溶剂分子分数模型,并应用于SN1反应
Floyd L Wiseman1, Dane W Scott2
1Department of Mathematics & Natural Science, Blue Mountain Christian University, P.O. Box 160, Blue Mountain, MS 38610, USA. fwiseman@bmc.edu.
Physical chemistry chemical physics : PCCP
|December 20, 2023
概括
一种新的热力学方法精确地分析了溶剂对化学反应的影响,超过了线性自由能量关系. 这种方法量化了共溶剂系统中的静电和溶解物-溶剂相互作用.
科学领域:
- 物理化学 物理化学
- 化学动力学 化学动力学
- 解决方案化学 解决方案化学
背景情况:
- 对溶剂对反应的影响的标准分析依赖于线性自由能量关系 (LFERs).
- LFER使用了许多溶剂参数,但对于特定的反应系统可能不可靠.
- 热力学方法提供了更高的精度,特别是在多组分溶剂系统.
研究的目的:
- 介绍数学形式主义,将激活自由能量与二进制溶剂系统中的大量热力学特性联系起来.
- 应用这种热力学方法来分析特定辅溶剂混合物中的反应速率.
- 为了区分和量化静电和溶解物-溶剂相互作用效应.
主要方法:
- 为二进制 (共溶剂) 系统开发了一种热力学形式主义.
- 使用选择的溶剂模型应用形式主义.
- 在受控条件下 (异分子分数,异极电,异热) 分析了三甲基化物在酸/水混合物中的水解速率.
主要成果:
- 与LFER相比,热力学方法提供了更精确的溶剂效应分析.
- 成功区分和量化了大量的静电效应和近距离的溶解物-溶剂相互作用.
- 证明了热力学方法对于理解辅溶剂系统中的反应动力学的实用性.
结论:
- 提出的热力学形式主义准确地将激活自由能量与二进制溶剂系统中的大量热力学特性联系起来.
- 这种方法为LFER提供了一个优越的替代方案,用于详细分析复杂混合物中溶剂效应.
- 该研究成功量化了静电和特定溶解物-溶剂相互作用对反应速率的不同贡献.
相关概念视频
02:25SN1 Reaction: Mechanism
11.9K
Kinetic studies of ionization of a tertiary halide in a protic solvent suggest that only the substrate participates in the rate-determining step (slow step). The nucleophile is involved only after the slowest step. The SN1 reaction takes place in a multiple-step mechanism.
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a...
Firstly, the haloalkane ionizes to generate a carbocation intermediate and a halide ion. This heterolytic cleavage is highly endothermic with large activation energy. The ionization of the substrate, facilitated by a...
11.9K
02:05Entropy and Solvation
7.1K
The process of surrounding a solute with solvent is called solvation. It involves evenly distributing the solute within the solvent. The rule of thumb for determining a solvent for a given compound is that like dissolves like. A good solvent has molecular characteristics similar to those of the compound to be dissolved. For example, polar solutions dissolve polar solutes, and apolar solvents dissolve apolar solutes. A polar solvent is a solvent that has a high dielectric constant (ϵ...
7.1K
02:24Ideal Solutions
19.6K
According to Raoult’s law, the partial vapor pressure of a solvent in a solution is equal or identical to the vapor pressure of the pure solvent multiplied by its mole fraction in the solution. However, Raoult's Law is only valid for ideal solutions. For a solution to be ideal, the solvent-solute interaction must be just as strong as a solvent-solvent or solute-solute interaction. This suggests that both the solute and the solvent would use the same amount of energy to escape to the...
19.6K
01:24Thermodynamics: Activity Coefficient
1.5K
Activity is the measure of the effective concentration of the species in solution. It can be expressed as the product of the molar concentration of the species and its activity coefficient. The activity coefficient is a dimensionless quantity and depends on the total ionic strength of the solution.
The activity coefficient is a measure of the deviation from ideal behavior. When the ionic strength of the solution is minimal, the activity coefficient of an ionic species is close to unity, making...
The activity coefficient is a measure of the deviation from ideal behavior. When the ionic strength of the solution is minimal, the activity coefficient of an ionic species is close to unity, making...
1.5K
02:27SN2 Reaction: Mechanism
14.4K
The kinetic studies of SN2 reactions suggest an essential feature of its mechanism: it is a single-step process without intermediates. Here, both the nucleophile and the substrate participate in the rate-determining step.
The presence of the more electronegative halogen in the substrate creates a polarized carbon-halide bond. The halide pulls the electron cloud generating an electrophilic center at the carbon atom. Thus, the carbon atom carries a partial positive charge while the halide has a...
The presence of the more electronegative halogen in the substrate creates a polarized carbon-halide bond. The halide pulls the electron cloud generating an electrophilic center at the carbon atom. Thus, the carbon atom carries a partial positive charge while the halide has a...
14.4K
01:09Theories of Dissolution: The Danckwerts' Model and Interfacial Barrier Model
310
Various dissolution theories provide insight into the factors that influence the dissolution rate. Danckwerts' Model suggests that turbulence, rather than a stagnant layer, characterizes the dissolution medium at the solid-liquid interface. In this model, the agitated solvent contains macroscopic packets that move to the interface via eddy currents, facilitating the absorption and delivery of the drug to the bulk solution. The regular replenishment of solvent packets maintains the...
310