アルケンの水酸化:冷却中に反応する熱い中間物質
David R Glowacki1, C H Liang, Stephen P Marsden
1School of Chemistry, University of Leeds, Leeds LS2 9JT, United Kingdom. david.r.glowacki@bristol.ac.uk
Journal of the American Chemical Society
|September 14, 2010
まとめ
化学反応における非統計的行動は,従来のモデルに異議を唱える. この研究では,主方程式モデルを使用して,溶液中であっても,熱い中間物質は完全な熱化前に反応することができ,統計モデルを保存することを示しています.
科学分野:
- 物理化学 物理化学
- 有機化学 オーガニック・ケミストリー
- 化学ダイナミクス 化学ダイナミクス
背景:
- 化学反応における非統計的行動が注目されています.
- 移行状態理論 (TST) の予測からの偏差は,標準的な化学反応性モデルに挑戦します.
研究 の 目的:
- 実験結果の代替解釈を提案する.
- 非統計的動的効果と統計的反応モデルの役割を調査する.
主な方法:
- 計算のために弱衝突ライス-ラムスペルガー-カッセル-マルカス (RRKM) -マスター方程式 (ME) モデルを使用しました.
- 溶液相熱反応のマスター方程式の方法論を適用した.
主要な成果:
- "熱い"中間物質は,溶液中の弱い衝突を介して段階的なリラックス中に反応することが示されました.
- TSTの予測から逸脱する実験結果の統計的解釈を提供した.
- マスター方程式を溶液相反応のための計算的に処理可能なモデルとして示した.
結論:
- マスター方程式は,特定の有機反応メカニズムを説明するために,従来のTSTの実行可能な代替案を提供します.
- 中間物質の段階的な衝突リラクゼーションは,様々な多原子系において一般的かもしれない.
- この研究は,溶液中の化学反応のダイナミクスを研究するための新しい計算アプローチを提供します.
関連する概念動画
02:47Alkynes to Aldehydes and Ketones: Hydroboration-Oxidation
Introduction
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
One of the convenient methods for the preparation of aldehydes and ketones is via hydration of alkynes. Hydroboration-oxidation of alkynes is an indirect hydration reaction in which an alkyne is treated with borane followed by oxidation with alkaline peroxide to form an enol that rapidly converts into an aldehyde or a ketone. Terminal alkynes form aldehydes, whereas internal alkynes give ketones as the final product.
02:36Regioselectivity and Stereochemistry of Hydroboration
A significant aspect of hydroboration–oxidation is the regio- and stereochemical outcome of the reaction.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
Hydroboration proceeds in a concerted fashion with the attack of borane on the π bond, giving a cyclic four-centered transition state. The –BH2 group is bonded to the less substituted carbon and –H to the more substituted carbon. The concerted nature requires the simultaneous addition of –H and –BH2 across the same face of the alkene giving syn stereochemistry.
03:08Hydroboration-Oxidation of Alkenes
In addition to the oxymercuration–demercuration method, which converts the alkenes to alcohols with Markovnikov orientation, a complementary hydroboration-oxidation method yields the anti-Markovnikov product. The hydroboration reaction, discovered in 1959 by H.C. Brown, involves the addition of a B–H bond of borane to an alkene giving an organoborane intermediate. The oxidation of this intermediate with basic hydrogen peroxide forms an alcohol.
02:34Regioselectivity and Stereochemistry of Acid-Catalyzed Hydration
The rate of acid-catalyzed hydration of alkenes depends on the alkene's structure, as the presence of alkyl substituents at the double bond can significantly influence the rate.
01:11Nucleophilic Aromatic Substitution: Elimination–Addition
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02:17Regioselectivity of Electrophilic Additions to Alkenes: Markovnikov's Rule
If a set of reactants can yield multiple constitutional isomers, but one of the isomers is obtained as the major product, the reaction is said to be regioselective. In such reactions, bond formation or breaking is favored at one reaction site over others.
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...
The hydrohalogenation of an unsymmetrical alkene can yield two haloalkane products, depending on which vinylic carbon takes up the halogen. However, one product usually predominates, where hydrogen adds to the vinylic carbon bearing the...