利用三甲基磷氧的31P NMR的化學位移及變化量來鑑定液態樣品的酸性程度

分子酸性是非常重要的化學特性之一。幾乎所有的化學反應都與溶劑效應有關。因此，使用光譜技術的方式獲得準確且有再現性的酸性表徵是十分重要的。本篇研究乃基於劉教授等人之實驗方法的基礎上予以延伸。實驗衍生於水和二甲基亞碸（DMSO）在pH計中pKa的比較，我們擴展了酸度的研究，以溶劑DMSO，得到三甲基磷氧（TMPO）分子的31P化學位移。在這項研究中，在DMSO為溶劑下TMPO分子作為酸性探針與酸解離出的質子作用。根據離子周圍概念和庫侖吸引力，電子雲密度從TMPO的氧帶部分負電荷轉移到酸液解離出的質子。因此，TMPO的31P化學位移值將隨著酸強度越強而移動到越低場。實驗結果證明，TMPO分子的31P化學位移比傳統的pH計可以檢測更大的範圍，範圍可以從弱酸到超強酸。將DMSO與水為溶劑的結果進行比較，在DMSO中弱酸或酸液低濃度具有較水更好的31P化學位移值的差異。

關鍵字

三甲基磷氧；核磁共振；二甲基亞碸；酸性鑑定

並列摘要

Solvent acidity is one of the most important chemical properties of a molecule. Almost all chemical reactions will be affected by the solvent effect. Therefore, it is essential to use the spectroscopy technology to obtain the accurate and reproducible acidic character of a solvent. Based on Liu et. al. works in acidic aqueous solutions, we extended the acidity studies to solvent dimethylsulfoxide (DMSO) to obtain 31P chemical shifts of the trimethylphosphine oxide (TMPO) molecule in order to compare the pKa values of acid molecules derived in pH meter with solvents of water and DMSO respectively. In this study, the TMPO molecule was used as the acidic probe to act with the proton dissociated from the acidic molecule in DMSO. According to the ion atmosphere concept and the Coulomb attraction force, the electron cloud density will shift from the partially negative-charged oxygen site of TMPO to the dissolved proton of the acidic molecule. Therefore, the 31P chemical shift value of TMPO will move to the downfield position. The stronger the acidic strength, the more downfield will be the chemical shift. The experimental results demonstrated that 31P chemical shifts of TMPO molecules in acidic DMSO solutions can detect wider acid strength range from superacids to weak acids than traditional pH meter does. Comparing with results obtained in acidic aqueous solutions, acidic molecules dissolved in DMSO have better 31P chemical shift differentiation especially for weak acids or strong acids at low concentrations than in their aqueous solutions.

並列關鍵字

trimethylphosphine oxide ； TMPO ； NMR ； DMSO ； acidity characterization

參考文獻

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利用三甲基磷氧的31P NMR的化學位移及變化量來鑑定液態樣品的酸性程度

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