| 研究生: |
蘇建源 Su, Jian-yuan |
|---|---|
| 論文名稱: |
以核磁共振技術和分子動力模擬探討乙氰和苯甲氰在1-羥乙基-3-甲基咪唑四氟硼酸鹽中的物理狀態 Studies on the physical states of acetonitrile and benzonitrile in 1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate by NMR techniques and molecular dynamics simulations |
| 指導教授: |
施良垣
Shy, Liang-Yuan |
| 學位類別: |
碩士 Master |
| 系所名稱: |
理學院 - 化學系 Department of Chemistry |
| 論文出版年: | 2009 |
| 畢業學年度: | 97 |
| 語文別: | 中文 |
| 論文頁數: | 181 |
| 中文關鍵詞: | 黏度 、導電度 、擴散係數 、離子液體 、Benzonitrile 、Acetonitrile 、HEMIMBF4 、核磁共振 、分子動力模擬 |
| 外文關鍵詞: | viscosity, conductivity, diffusion coefficient, acetonitrile, benzonitrile, ionic liquid, HEMIMBF4, nuclear magnetic resonance, molecular dynamics simulations |
| 相關次數: | 點閱:120 下載:4 |
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本篇以核磁共振的方法,觀察1-羥乙基-3-甲基咪唑四氟硼酸鹽
(簡稱HEMIMBF4)分別加入稀釋劑 Acetonitrile (AN) 與 Benzonitrile (BN) 後,稀釋劑含量及溫度的改變,對於化學位移、擴散係數及遲緩時間(1H、19F) 之影響。本篇同時也測量混合液之黏度、密度與比導電度等巨觀性質,並佐以分子動力模擬以期對於離子的擴散與導電有更深入的瞭解。
結果顯示,HEMIM+之H2、H10、H5 與H4原子的化學位移偏差之大小為H10 >H2 >H5 ~ H4。這顯示H10 (羥基之氫原子)與BF4-及稀釋劑的氫鍵作用力較H2(五圓環上兩個氮之間的氫原子)者強。此結果與分子模擬所得的電荷密度相符合。此外,由NOESY 光譜得知純HEMIMBF4主要是以大離子團進行運動。當稀釋劑之含量增加時,大離子團逐漸被拆開,而以小離子團的形式出現,此結果可由分子動力模擬得到印證。
BF4- 離子的擴散係數大於HEMIM+ 離子者,且XAN為0.8時之陽離子擴散係數較0.7者大許多,這是因為HEMIM+ 離子周圍配位之AN分子數急遽增加所致。
當稀釋劑含量增加時,溶液黏度也隨之下降,遲緩時間上升,離子之擴散速率及比導電度均隨之遞增。這些現象可由分子動力模擬所得的配位數、自由離子比率與離子群之平均離子數獲得解釋。
在相同的溫度及稀釋劑莫耳分率下,BN與HEMIM+的作用力較AN者強。含BN系統離子之Stokes-Einstein半徑較AN者小,故其擴散係數與導電度均較AN系統者大。此結果可由陽離子周圍稀釋劑個數、平均自由離子機率、稀釋劑之莫耳體積及混合液之黏度獲得解釋。
根據分子動力模擬之結果,本篇繪出以HEMIM+離子為中心的周圍環境示意圖,這些圖對於實驗的微觀解釋有實質的幫助。
Nuclear magnetic resonance techniques have been applied to investigate the influences of diluent type, diluent content and temperature on the chemical shift, diffusion coefficient and the relaxation time for
1-(2-hydroxyethyl)-3-methylimidazolium tetrafluoroborate (HEMIMBF4).The macroscopic properties, like viscosity, density and conductivity of the mixture were measured.
To understand further the details of ionic diffusion and conductivity, molecular dynamics simulations were also conducted.
It’s known from the experiment that the 1H chemical shift difference has the order:H10>H2>H5~H4, which indicates that the hydroethyl hydrogen atom of HEMIM+ ion forms a stronger hydrogen bond with BF4- ion and diluent molecules than any other hydrogen atoms. The result is in accord with the partial charge obstained from the simulations.
The NOESY spectra shows that most of the ions in pure HEMIMBF4 aggregate to form large clusters, the size of which diminishes with the increase of diluent content, which is further confirmed by the simulations.
In general, the diffusion coefficient of BF4- ion is greater than that of HEMIM+ ion. The diffusion rate of HEMIM+ at a acetonitrile (AN) molar fraction (XAN) of 0.8 is far greater than that at 0.7, owing to the rapid increase of coordinating acetonitrile molecules around HEMIM+ ion.
As the diluent content increases, the viscosity of solution decreases, but the relaxation time, diffusion rate and specific conductivity increases. These phenomena can be interpreted with the coordination number, free ion fraction and ionic cluster size that are obtainable from the simulations.
At constant temperature and diluent concentration, benzonitrile molecule has stronger interaction with HEMIM+ than AN. For HEMIMBF4 / BN system, the Stokes-Einstein radius is smaller than that of AN containing system, which leads to the high diffusion rate and conductivity.
The origin can be traced back to the differences in the coordination number, free ion fraction, diluent size and solution viscosity.
Based on this work, the surroundings around the HEMIM+ ion is now clear, which is believed to be helpful for the microscopic explanation of experimental observations.
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