二次デウテリウムイソトープは,カルボキシル酸とフェノール酸の酸性に影響する
Charles L Perrin1, Yanmei Dong
1Department of Chemistry 0358, University of California-San Diego, La Jolla, California 92093-0358, USA. cperrin@ucsd.edu
Journal of the American Chemical Society
|March 16, 2007
まとめ
酸性に対するデウテリウム同位体 (IEs) の影響は,炭酸酸およびフェノールについて測定されました. デュテレーションにより酸度が低下し,デュテリウムの位置に関係なく,芳香酸のIEは驚くほど定常であった.
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
- イソトープ効果とは
背景:
- 二次デウテリウム同位体効果 (IEs) は,分子構造と結合に関する洞察を提供します.
- 酸性や陽子転移の仕組みを理解することは,化学において極めて重要です.
研究 の 目的:
- 炭酸酸とフェノールの酸性に対する二次デウテリウム同位体の影響を正確に測定する.
- これらの同位体効果に対するデュテリウムの位置の影響を調査する.
- 二次性デウテリウム同位体効果の起源を計算的方法を用いて解明する.
主な方法:
- 同位体の混合物における同位体効果を測定するためのNMR定位法.
- Ab initio 理論的サポートのための計算化学.
主要な成果:
- デュテレーションにより酸度が一貫して低下する (DあたりDeltapKで0.031まで).
- IEsは,アリファ酸の酸性陽子からの距離とともに減少する.
- 驚くべき発見:フェノールとベンゾ酸のIEは,デュテリウムの位置 (オルト,メタ,パラ) にかかわらず恒定である.
- Ab initio計算は実験的なIEを過大評価し,解答に起因しない不一致がある.
結論:
- 二次性デウテリウム同位体効果は,主として,脱プロトン化時に同位体感度の高い振動のゼロポイントエネルギーの変化によって支配される.
- アロマティック酸の場合は,振動分析と電子密度が観測されたIEを説明し,単純な移位または誘導効果と矛盾する.
- この研究は,これらの同位体効果の誘導的起源に対する証拠を提供します.
関連する概念動画
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01:25Acidity and Basicity of Carboxylic Acid Derivatives
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The relative acidic strength of the derivatives can be explained based on the extent of resonance stabilization of the conjugate base. The...
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Carboxylic acids are easily identified by dissolving them in deuterium oxide, which results in a rapid exchange of the acidic protons with deuterium. This leads to the disappearance of the acidic...
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Binary Acids and Bases
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In the absence of any leveling effect, the acid strength of binary compounds of hydrogen with nonmetals (A) increases as the H-A bond strength decreases down a group in the periodic table. For group 17, the order of increasing acidity is HF < HCl < HBr < HI. Likewise, for group 16, the order of increasing acid strength is H2O < H2S < H2Se < H2Te. Across a row in the periodic table, the acid strength of binary hydrogen compounds increases with increasing...