イオン性ガンマ除去を協調して行うことができるか:サイクロブータン環を横断して内部位移を計測する
Uri Habusha1, Esther Rozental, Shmaryahu Hoz
1Department of Chemistry, Bar-Ilan University, Ramat-Gan, Israel 52900.
Journal of the American Chemical Society
|December 12, 2002
まとめ
この研究では,カルバニオン除去速度を定量化し,約3 x 10^10 s^-1.の急速な内部除去速度定数を示しました. 計算分析により,この除去は,特定の条件下で障壁なく発生することを示唆しています.
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
- コンピューティング・ケミストリー
背景:
- カーバニオンは,有機合成における重要な中間物質である.
- 陽子化と除去を含むカルバニオン反応経路を理解することは極めて重要です.
- 3-クロロビサイクロブタン-カルボニトリルは,カルバニオンの振る舞いを研究するためのモデル基板として機能します.
研究 の 目的:
- カーバニオン中間物質の内部排出の速度定数を決定する.
- 陽子ドナー酸度が,陽子化と除去の間のカルバニオン分割に及ぼす影響を調査する.
- カルバニオン除去機構を計算的にモデル化し,溶解の役割を評価する.
主な方法:
- 酸度が異なる一連のアルコールを用いて,製品の比率 (プロトネーション/エミリネーション) を実験的に決定する.
- エイゲン型グラフを用いた実験データの分析.
- 排除プロセスをモデル化するために,Ab initio計算 (B3LYP/6-31G) を行う.
- 溶解効果を含む反応ダイナミクスのシミュレーション (Onsagerモデル).
主要な成果:
- プロトネーションとエミリテーションの間の製品の分割は,内部エミリテーション速度の定数を約3 x 10^10 s^-1として決定することを可能にしました.
- 高酸性アルコール (トリフルオロエタノールとヘキサフローロ-2-プロパノール) は,拡散制御反応率をもたらした.
- 計算による研究は,溶解の欠如でモデルカルバニオンのための障壁のない除去プロセスを示しました.
- ディメトキシエタン (DME) の溶解効果は,カルバニオンを安定させ,自発的な排出を妨げることが示されました.
結論:
- 研究されたカルバニオンの内部除去は,急速なプロセスです.
- 溶解は,カルバニオン反応性を制御する上で重要な役割を果たします.
- 計算および実験データは,カルバニオン反応経路の包括的な理解を提供します.
さらに関連する動画
12:19Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
Published on: November 29, 2018
10:17Efficient Construction of Drug-like Bispirocyclic Scaffolds Via Organocatalytic Cycloadditions of α-Imino γ-Lactones and Alkylidene Pyrazolones
Published on: February 7, 2019
関連する概念動画
02:30Stability of Substituted Cyclohexanes
This lesson discusses the stability of substituted cyclohexanes with a focus on energies of various conformers and the effect of 1,3-diaxial interactions.
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
The two chair conformations of cyclohexanes undergo rapid interconversion at room temperature. Both forms have identical energies and stabilities, each comprising equal amounts of the equilibrium mixture. Replacing a hydrogen atom with a functional group makes the two conformations energetically non-equivalent.
For example, in...
02:38Electrophilic Addition to Alkynes: Halogenation
Introduction
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
Halogenation is another class of electrophilic addition reactions where a halogen molecule gets added across a π bond. In alkynes, the presence of two π bonds allows for the addition of two equivalents of halogens (bromine or chlorine). The addition of the first halogen molecule forms a trans-dihaloalkene as the major product and the cis isomer as the minor product. Subsequent addition of the second equivalent yields the tetrahalide.
01:26Thermal and Photochemical Electrocyclic Reactions: Overview
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
01:17Thermal Electrocyclic Reactions: Stereochemistry
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
01:18Aromatic Hydrocarbon Cations: Structural Overview
Cycloheptatriene is a neutral monocyclic unsaturated hydrocarbon that consists of an odd number of carbon atoms and an intervening sp3 carbon in the ring. The three double bonds in the ring correspond to 6 π electrons, which is a Huckel number, and therefore satisfies the criteria of 4n + 2 π electrons. However, the intervening sp3 carbon disrupts the continuous overlap of p orbitals. As a result, cycloheptatriene is not aromatic.
Removing one hydrogen from the intervening CH2 group with both...
Removing one hydrogen from the intervening CH2 group with both...
01:17Pericyclic Reactions: Introduction
Pericyclic reactions are organic reactions that occur via a concerted mechanism without generating any intermediates. The reactions proceed through the movement of electrons in a closed loop to form a cyclic transition state, where rearrangement of the σ and π bonds yields specific products.
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...
Pericyclic reactions can be classified into three categories: electrocyclic reactions, cycloaddition reactions, and sigmatropic rearrangements. Electrocyclic reactions and sigmatropic rearrangements are...