理論研究取代基對N-salicylidene-alkylamines的分子內氫鍵及互變異構作用的影響

Theoretical Study on Influence of Intramolecular Hydrogen Bonds and Enol Imine ↔ Keto Amine Tautomerism in N-Salicylidene-Alkylamines by Various Substituted Groups

10.6202/THJ-2014-10-02

蔡明松(Ming-Sung Tsai)

互變異構作用 ； 共振增強氫鍵 ； 密度泛函理論 ； schiff bases ； tautomerism ； Resonance-Assisted Hydrogen Bonding (RAHB) ； density functional theory (DFT)

慈惠學報

10期（2014 / 12 / 01）

12 - 24

繁體中文

80年代末Gilli等人研究1,3-diketones、β-enaminones、ketohydrazones等發現這類分子中存有一種特殊的氫鍵稱為共振增強氫鍵［Resonance-Assisted Hydrogen Bonding(RAHB)］。此類氫鍵比一般氫鍵有較短的氫鍵鍵長、較強鍵能、及較小質子轉移的能量障壁。為了更容易瞭解共振增強氫鍵，運用酸、鹼理論來討論氫鍵，將氫鍵［R－D-H…:A－R'］其中R－D－H是質子的提供者，:A－R'是為質子接受者。本研究運用量子化學方法，密度泛函理論（density functionaltheory；DFT）計算方法探討運用不取代基來改變schiff bases中質子提供者酚的pKa值及改變質子接受者對schiff bases的O－H…N=氫鍵的影響及對進行enol imine（phenol）↔ ketoamine（quinine）互變異構作用的影響。計算結果顯示改變schiff bases中質子提供者酚的pKa值愈小，O-H…N=的鍵長愈短及enol imine（phenol）↔ keto amine（quinine）互變異構作用的能量障壁愈小。這結果顯示質子提供者的酸性愈強，schiff bases的共振增強氫鍵就越強。而質子接受者的pKb 值小越強，其O-H…N=氫鍵就越強。

The effect of chemical substitutions on the intramolecular hydrogen bond and tautomerism of the salicylidene methylamine molecules are studied with the aid of density functional theory methods. Calculations predict the predominance of enol imine form in schiff bases in the gas phase. It is shown that decreasing pKa of phenols increases strength of intramolecular hydrogen bond of schiff base. From computational results, it is futher concluded that: (1) increasing pKa of phenols decreases the energy barriers of proton transfer for schiff bases; (2) increasing strength of intramolecular hydrogen bond causes the difference in energy of tautomers is distinctly less; (3) increasing strength of intramolecular hydrogen bond incresaes amount of the keto form of schiff bases.

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