ガス相におけるn,pi*刺激状態の消火:絶対反応性と選択性の変動
Dieter Klapstein1, Uwe Pischel, Werner M Nau
1Department of Chemistry, St. Francis Xavier University, Antigonish, Nova Scotia B2G 2W5, Canada.
Journal of the American Chemical Society
|September 19, 2002
まとめ
電子ドナーによる刺激されたアゾアルカンのガス相消火は,エクシプレックスと直接の水素転送を含むメカニズムを明らかにします. 溶解は,特に極性O-HとN-H結合の反応性に大きな影響を与える.
科学分野:
- フォトケミストリー フォトケミストリー
- 化学動力学 化学動力学
- 有機化学 オーガニック・ケミストリー
背景:
- アゾアルカンは,電子と水素のドナーによって消火されやすいn,pi*-excited状態を示します.
- ガス相における消火メカニズムを理解することは,溶液中の溶媒の効果を解釈する上で極めて重要です.
研究 の 目的:
- 様々なヘテロアトムを含むドナーによって活性化されたアゾアルカンのガス相消火機構を調査する.
- エクシプレックス形成と直接水素移転の役割を解明する.
- ガス相反応性と溶液相観測,特に逆転溶媒効果を比較する.
主な方法:
- 2,3-diazabicyclo[2.2.2]oct-2-eneと19の異なるドナー (アミン,硫化物,エーテル,アルコール) を使用したガス相消火実験.
- 9種類のデュテラートアゾアルカンの誘導体に対するデュテリウム同位体効果の測定.
- 反応速度の運動分析と,ガス相と溶液相の比較.
主要な成果:
- 三次アミンおよび硫化物との刺激された電荷伝送複合体 (エクシプレックス) の証拠.
- C-H,N-H,およびO-H結合からの競争的な直接水素転送の識別.
- ガス相速度の定数は溶液よりも大幅に大きく,反転溶媒効果を支えている.
- 極性O-HおよびN-H結合は,より極性のないC-H結合と比較して,溶解時により大きな反応性低下を示します.
結論:
- この研究は,特定のドナーに対するエクシプレックス関わりと,ガス相アゾアルカンの冷却における他のドナーに対する直接的な水素転送を支持している.
- ガス相運動学は,溶液で観察される"逆の溶媒効果"についての洞察を提供します.
- 溶解は,光誘導水素抽象化における極性対非極性結合の反応性に差異的な影響を及ぼします.
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