微溶解アニオンのガス相S(N) 2反応におけるα効果を調査する
Ditte L Thomsen1, Jennifer N Reece, Charles M Nichols
1Department of Chemistry, University of Copenhagen , Universitetsparken 5, Copenhagen, DK-2100 Denmark.
Journal of the American Chemical Society
|September 20, 2013
まとめ
この研究では,アルファ効果は,単一の水分子の場合でも,マイクロソルバテド核性粒子の反応性を高めることが示されています. これはアルファ効果を証明している.
科学分野:
- 物理化学 物理化学
- 化学動力学 化学動力学
- コンピューティング・ケミストリー
背景:
- アルファ効果は,隣接する単一ペアによる核愛子の反応性の強化を記述する.
- 以前の研究では,ヒドロペロキシドアニオン (HOO−) のガス相S(N) 2反応におけるアルファ効果が実証されました.
- アルファ効果に対する溶解の影響については,さらなる調査が必要である.
研究 の 目的:
- ガス相S(N) 2反応におけるアルファ効果に対する微溶解の影響を調査する.
- マイクロソルバテドアルコキシアニオン (RO−(H2O)) とマイクロソルバテドアルコキシアニオン (HOO−(H2O)) の反応性を比較する.
- アルファ効果における微分溶解の役割を明らかにする.
主な方法:
- ガス相イオン-分子の反応を研究するために,流れるアフターグロー選択イオンフローチューブ装置を使用しました.
- メチル塩化物 (CH3Cl) とのマイクロソルバテドヌクレオフィル (HOO−(H2O) とRO−(H2O)) のS(N) 2反応を調査した.
- 移行状態構造と溶解相互作用を分析するために理論的計算を行った.
主要な成果:
- マイクロ溶解した水酸化物アニオン (HOO−(H2O)) は,水分子の存在におけるアルファ効果を確認し,反応性が向上した.
- マイクロソルバテド・ヌクレオフィルはより大きなブロンステッド・βnuc値を示し,未溶解のヌクレオフィールと比較して後の移行状態を示した.
- 移行状態での差分解が観察され,アルファ効果への貢献を示唆した.
- 製品分布は,水素化されたクラスター (Cl−(H2O)) よりも,裸の塩化アニオン (Cl−) の形成が好ましいことを示した.
結論:
- アルファ・エフェクトは,マイクロソルバテッドのα-核愛者にさえも存在し,有意である.
- 溶解はアルファ効果に大きく影響し,微分溶解が重要な役割を果たします.
- ヒドロペロキシドアニオン (HOO−) は,微溶解したクラスター反応の活性ヌクレオファイルのままである.
関連する概念動画
02:25SN1 Reaction: Mechanism
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 polar...
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 polar...
02:26SN2 Reaction: Transition State
An SN2 reaction of an alkyl halide is a single-step process in which bond formation between the nucleophile and the substrate and bond breaking between the substrate and the halide occurs simultaneously through a transition state without forming an intermediate.
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
When the nucleophile approaches the electrophilic carbon with its lone pairs, the halide acts as a leaving group and moves away with the electron-pair bonded to the carbon. Dotted partial bonds represent the bonds being formed or broken...
01:17Reactions of α-Halocarbonyl Compounds: Nucleophilic Substitution
Nucleophilic substitution in α-halocarbonyl compounds can be achieved via an SN2 pathway. The reaction in α-haloketones is generally carried out with less basic nucleophiles. The use of strong basic nucleophiles leads to the generation of α-haloenolate ions, which often participate in other side reactions.
02:27Predicting Products: SN1 vs. SN2
Nucleophilic substitution reactions of alkyl halides can proceed via an SN1 or an SN2 mechanism. While in SN2 reactions, the nucleophile attacks the substrate simultaneously as the leaving group departs, in SN1 reactions, the substrate first dissociates to give the carbocation intermediate. Various factors such as the structure of the substrate, the strength of the nucleophile, and the nature of the solvent promote one mechanism over the other.
With increased substitution on the alkyl halide,...
With increased substitution on the alkyl halide,...
02:23SN2 Reaction: Stereochemistry
In an SN2 reaction, the nucleophilic attack on the substrate and departure of the leaving group occurs simultaneously through a transition state. As the nucleophile approaches the substrate from the back-side, the configuration of the substrate carbon changes from tetrahedral to trigonal bipyramidal and then back to tetrahedral, leading to an inversion in the configuration of the product.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
If the substrate is an achiral molecule at the α-carbon, the inversion of configuration is not observed.
01:14Nucleophilic Aromatic Substitution of Aryldiazonium Salts: Aromatic SN1
Treating arylamines with nitrous acid gives aryldiazonium salts that are effective substrates in nucleophilic aromatic substitution reactions. The diazonio group in these salts can be easily displaced by different nucleophiles, yielding a wide variety of substituted benzenes. The leaving group departs as nitrogen gas, and this easy elimination is the driving force for the substitution reaction.
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...
In the Sandmeyer reaction, for example, the diazonio group is replaced by a chloro, bromo, or cyano...