分子内反応の速度の上昇におけるエントロピーの役割
Anthony A Armstrong1, L Mario Amzel
1Department of Biophysics and Biophysical Chemistry, Johns Hopkins University School of Medicine, 725 North Wolfe Street, Baltimore, MD 21205-2185, USA.
Journal of the American Chemical Society
|November 20, 2003
まとめ
アクセシブルな基底と移行状態のエントロピーの差は,分子内凝縮反応速度に大きな影響を及ぼします. 振動性ではなく,適合性エントロピーは,これらの反応における活性化自由エネルギーの主要な原動力である.
科学分野:
- 有機化学 オーガニック・ケミストリー
- 物理化学 物理化学について
- 化学動力学 化学動力学
背景:
- 分子内凝縮反応は有機合成において極めて重要です.
- 反応速度は,反応する分子の構造によって影響されることが知られています.
研究 の 目的:
- ディカルボキシル酸モノエステルの分子内凝縮の速度変動のエントロピー起源を調査する.
- アクティベーション自由エネルギーに対する構成および振動エントロピーの貢献を決定する.
主な方法:
- 基底状態コンフォマーと移行状態のようなコンフォマー間のエントロピー差 (DeltaS(NAC,S)) の推定.
- 推定DeltaS ((NAC,S)) と実験的に決定された反応速度定数との相関分析.
- 振動エントロピーの貢献を評価するための正常モード分析.
主要な成果:
- デルタS ((NAC,S)) と反応率 (R ((2) = 0.96 と 0.73) の間には強い相関が観察されました.
- 正常モード分析では,振動エントロピーの変化の寄与が最小であることを示した.
- 適合エントロピーの差異は有意であることが判明しました.
結論:
- 基本状態と移行状態の適合エントロピーの差異は,活性化の自由エネルギーにおける主要な要因である.
- この研究では,分子内凝縮反応の運動を制御するエントロピー要因を明らかにした.
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