S(N) 1 から S(N) 2 のメカニズムへの変化を予測することはできますか?
Thanh Binh Phan1, Christoph Nolte, Shinjiro Kobayashi
1Department Chemie und Biochemie der Ludwig-Maximilians-Universität München, Butenandtstrasse 5-13 (Haus F), 81377 München, Germany.
Journal of the American Chemical Society
|July 29, 2009
まとめ
この研究では,ベンジヒドリルブロミドとアミンの反応は,同時進行するS(N) 1とS(N) 2経路を経由して進行することを明らかにしました. S(N) 2メカニズムは,ベンジヒドリリウムイオン寿命がそれを必要とする場合にのみ好まれ,中間の安定性に基づくシフトを示します.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 反応の動力学
- 物理有機化学 物理有機化学
背景:
- 置換されたベンジヒドリルブロミドは,DMSO内のアミンと反応し,アミン,ベンゾフェノン,ベンジヒドロールを生成する.
- 運動分析は,アミン依存性 (S(N) 2) とアミン依存性 (S(N) 1) の経路を並行して示す速度法則を明らかにする.
研究 の 目的:
- 置換されたベンジヒドリルブロミドとアミンの間の反応のメカニズムを解明する.
- 反応条件と中間寿命に基づいてS(N) 1とS(N) 2プロセスの相互作用を調査する.
- 一般化された速度方程式を使用して,核愛者と電愛者のパラメータを定量化します.
主な方法:
- 速度の法則を決定するために,20°Cでの動力学的調査.
- 速度の定数とハメットのシグマ (((+)) 定数の相関は,S (((N)) 1の反応について.
- log k = s(E + N) の方程式をS(N) 1 / S(N) 2の移行を分析するために適用する.
- レーザーフラッシュ光分解を用いたベンジヒドリリウムイオンの生成.
主要な成果:
- 同時にS(N) 1とS(N) 2の反応メカニズムの証拠が観察されました.
- S(N) 1の比率は置換効果と相関する (rho = -3.22),S(N) 2の比率は相関せず,異なる移行状態を示す.
- S(N) 2メカニズムへの移行は,ベンジヒドリリウムイオン中間物の寿命が振動限界に達することと関連していました.
- DMSOは,水とアルコールよりも強いO核愛者として特定されました.
結論:
- 反応機構は,ベンジヒドリリウムイオンの寿命が核愛者との反応速度によって制限される場合,S(N) 1からS(N) 2に移行する.
- この研究は,カルボケーション中介物質を含む核愛性置換反応を理解するための定量的な枠組みを提供します.
- DMSOの核好性は,他のO核好性と比較して特徴付けられました.
さらに関連する動画
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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...
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02:14SN2 Reaction: Kinetics
Kinetic Studies and Significance
In a chemical reaction, a relationship exists between the concentration of reactants and the rate at which the reaction proceeds. The study to measure this relationship is known as the kinetics of a chemical reaction. Kinetic studies are used to deduce the rate law of a chemical reaction, which provides information about the species involved during the transition state of the rate-determining step. Thus, kinetic studies help to derive the mechanism of a reaction.
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02:26SN2 Reaction: Transition State
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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...
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02:27Predicting Products: SN1 vs. SN2
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With increased substitution on the alkyl halide,...
With increased substitution on the alkyl halide,...
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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.
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.
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