中性过渡金属化物作为结和质子转移中的酸:介质极性和特定的溶解效应
Vladislava A Levina1, Oleg A Filippov, Evgenii I Gutsul
1A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilov Street 28, 119991 Moscow, Russia.
Journal of the American Chemical Society
|August 12, 2010
概括
有机金属化物中的弱键影响质子转移反应. 特定的溶剂相互作用可能会意外地阻碍这种转移,影响化学反应.
科学领域:
- 有机金属化学 有机金属化学
- 物理化学 物理化学
- 计算化学计算化学
背景情况:
- 有机金属化物,如CpM ((CO)) ((3) H (M = Mo, W) 是化学反应的关键.
- 了解它们与有机基的相互作用对于阐明反应机制至关重要.
- 涉及这些化物的质子转移反应是催化和合成的基础.
研究的目的:
- 研究弱键复合物的结构,光谱和电子特征.
- 为了确定可逆质子转移步骤的热力学参数.
- 阐明溶剂对结和质子转移的影响.
主要方法:
- 使用可变温度红外 (IR) 光谱学的实验性确定.
- 使用密度函数理论 (DFT/M05) 和频率计算进行计算分析.
- 使用IR和导体式极化连续模型 (CPCM) 的计算,对六,二甲 (CH(2)Cl(2)),四基 (THF) 和乙二 (CH(3) CN进行溶剂效应研究.
主要成果:
- 在CpM(CO) ((3) H化物和各种有机基之间的弱结合复合物的表征.
- 测定热力学参数 (ΔH°,ΔS°) 在中可逆的质子转移步骤.
- 确定增强键形成并影响质子转移平衡的特定溶解效应.
结论:
- 弱键在这些有机金属化物的质子转移机制中起着重要作用.
- 与THF和CH(3) CN等溶剂的竞争性弱相互作用可以调节化物和基活性.
- 溶剂的选择对质子转移产生了重大影响,相比于非极性,中度极性溶剂有时会反直觉地阻碍反应.
相关概念视频
01:01Acid Halides to Carboxylic Acids: Hydrolysis
Hydrolysis of acid halides is a nucleophilic acyl substitution reaction in which acid halides react with water to give carboxylic acids. The reaction occurs readily and does not require acid or a base catalyst.
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
As shown below, the mechanism involves a nucleophilic attack by water at the carbonyl carbon to form a tetrahedral intermediate. This is followed by the reformation of the carbon–oxygen π bond along with the departure of a halide ion. A final proton transfer step yields carboxylic acid...
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...
02:54Ions as Acids and Bases
Salts with Acidic Ions
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
Salts are ionic compounds composed of cations and anions, either of which may be capable of undergoing an acid or base ionization reaction with water. Aqueous salt solutions, therefore, may be acidic, basic, or neutral, depending on the relative acid-base strengths of the salt’s constituent ions. For example, dissolving the ammonium chloride in water results in its dissociation, as described by the equation:
03:38Polyprotic Acids
Acids are classified by the number of protons per molecule that they can give up in a reaction. Acids such as HCl, HNO3, and HCN that contain one ionizable hydrogen atom in each molecule are called monoprotic acids. Their reactions with water are:
02:12Solvating Effects
An understanding of the solvating effect helps rationalize the relation between solvation and acidity of the compound. In addition, this also explains the relative stability of conjugate bases for compounds with different pKa values. This lesson details, in-depth, the principle of solvating effects. The strength of an acid and the stability of its corresponding conjugate base are determined using pKa values. This observed relationship is a consequence of solvation, which is the interaction...
02:11Leveling Effect and Non-Aqueous Acid-Base Solutions
This lesson defines the leveling effect in acidic and basic solutions and its role in aqueous and non-aqueous solutions. It is essential to understand the competing nature of various species in a chemical system.
The Leveling Effect of a Solvent
A generic acid (HA) reacts with the generic base (B-) to yield the corresponding conjugate base (A-) and conjugate acid (HB):
The Leveling Effect of a Solvent
A generic acid (HA) reacts with the generic base (B-) to yield the corresponding conjugate base (A-) and conjugate acid (HB):