C中心のルイス酸 (カルボカチオン) に向かって,ルイス基本性のスケール
Herbert Mayr1, Johannes Ammer, Mahiuddin Baidya
1Department Chemie, Ludwig-Maximilians-Universität München , Butenandtstraße 5-13, Haus F, 81377 München, Germany.
Journal of the American Chemical Society
|January 3, 2015
まとめ
この研究では,ベンジヒドリリウムイオンのルイス酸性と,様々な塩基のルイス塩基性を定量化し,反応性のスケールを確立しました. それは,反応性,ルイス酸性,および計算されたメチルアニオン相性との間の線形相関を明らかにし,速度-均衡関係のための境界を定義します.
科学分野:
- 物理有機化学 物理有機化学
- コンピューティング・ケミストリー
- 化学熱力学 化学熱力学
背景:
- ベンゾヒドリルカチオン (Ar2CH(+)) は,ルイス酸度が異なる重要なカルボカチオンである.
- ルイス酸と塩基の反応性を理解することは,有機化学において極めて重要です.
- 以前の研究では,ルイス酸塩基均衡を調査しましたが,ベンジヒドリリウムシステムについては包括的なスケールがありませんでした.
研究 の 目的:
- ベンジヒドリリウムイオンとルイス基間の反応の均衡定数を決定する.
- ベンジヒドリリウムイオンのルイス酸度 (LA) と様々な塩基のルイス塩度 (LB) の定量尺度を作成する.
- 熱力学特性 (LA) と運動特性 (反応率) と計算データ (メチルアニオン相性) を相関させる.
主な方法:
- ディクロロメタンとアセトニトリルにおける平衡定数の光度測定で20°Cでの測定.
- 最小二乗最小化により,LAとLBのスケールを導出し,LA=0で (4-MeOC6H4) 2CH(+) の最小二乗最小化を行う.
- メチルアニオンの相性について,同熱の定位カロメトリと量子化学計算 (B3LYP) を行う.
主要な成果:
- 18個のベンジヒドリリウムイオンに対するルイス酸度尺度を開発し,18個の大きさのオーダーをカバーしました.
- 56の異なる基数に対するルイスの基本を確立した.
- ルイス酸度,メチルアニオン相性,およびSN1溶解率の間の優れた線形相関が反応性カルボケーションの間で発見されましたが,安定した場合は偏差がありました.
- ドナー置換イオンに対する電友反応性とルイス酸性の間の線形相関を特定し,受容体置換イオンが予測よりも遅い反応を示した.
結論:
- 定量的なルイス酸性および塩基性スケールは,ベンジヒドリリウムシステムのために成功裏に確立されました.
- メチルアニオンの親和性は,ルイス酸性に対する信頼できる計算予測器として機能します.
- 線形速度の均衡関係の限界を定義し,カルボケーションの安定性と置換剤の種類に基づく違いを強調した.
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