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| 研究生： |
孫秉鍵 Sun, Bian-Jian |
|---|---|
| 論文名稱： |
以理論計算的方式進行(1)不同系列的熔鹽中氫鍵之影響及(2)CFxH4-x 及 BFxH4-x- 內的負超共軛現象之研究 Studies of (1) H-bonding in various series of Ionic Liduids and (2) Negative Hyper -conjugation(NHC) in CFxH4-x- and BFxH4-x- by Molecular Calculations |
| 指導教授： |
王小萍
Wang, Shao-Pin |
| 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： | 2003 |
| 畢業學年度： | 91 |
| 語文別： | 中文 |
| 論文頁數： | 127 |
| 中文關鍵詞： | 熔鹽 、負超共軛 、氫鍵 |
| 外文關鍵詞： | Ionic Liquids, Molten Salts, Negative hyperconjugation |
| 相關次數： | 點閱：102 下載：1 |
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在熔鹽的眾多研究中，當某些熔鹽離子對中可能有氫鍵這問題被提出後，已吸引了許多人投入這項研究。在本研究中，我們選擇以理論計算的方式來研究含有BF4- 或 PF6- 的離子對中的氫鍵。本研究採用的陽離子分別為ammonium ions, pyridium ion 以及某些 imidazolium ions (Im+)。經由分析B-F•••H 中氫與氟的距離，可觀察到 NR3H+ 陽離子與 BF4- 所形成的離子對的氫鍵最強，再來是 PyH+最弱的是Im+ 陽離子。分析其軌域作用能量亦可得到相同的結論。如果將離子對中的陰離子改為 PF6- 依舊可得到如 BF4- 時的結果。而在 ammonium ions （氨鹽陽離子）系列中發現不管陰離子為 BF4- 或PF6- 其傾向皆為 NH4+ > NR3H+ > NR2H2+NRH3+。
19F 及 31P （I皆為1/2）因為其磁旋比高且其天然含量高（約100%），因此其NMR 光譜靈敏度高，僅次於氫，因此從他們的化學位移變化來研究氫鍵的形成應該會是很好用的光譜技術。31P 的核磁共振光譜的偶極-偶極（dipole-dipole）弛緩時間測定的實驗亦可提供為研究氫鍵之方法。至於11B的核磁共振光譜的四極（quadrupolar）弛緩時間測定的實驗最近已被引用來測定氫鍵訊息。
另外，在氟甲烷的E(2)分析中發現，當氟的取代數目增加時，其負超共軛（NHC）的作用能量也跟著增加。這個現象也由各種不管是理論計算或是實際的實驗得到相同的結果。經由E(2)值的分析，我們發現NHC可用於判斷BFxH4-x 系列中其B-F鍵結的強度。更進一步，我們發現 NHC 可用來解釋 BF4- 的氟原子上的負電荷為何減少到幾乎與 PF6- 的氟原子相近。因此我們也認為 NHC 是造成 BF4- 在與陽離子形成氫鍵的能力不如預期強的重要原因。
Hydrogen bonding between the counter ions for a number of room temperature ionic liquids has attracted numerous research interests. In the present work, we perform a theoretical investigation of H-bonding in ion pairs containing BF4- or PF6-. The cations under this study are ammonium ions, pyridium ion and some imidazolium ions (Im+). Through the B-F•••H distances, it is found that the NR3H+ cations form strongest H-bonding with BF4-, followed by PyH+ and then the Im+ cationss. Analysis of the values of orbital interaction energies also leads to the same conclusion. The same studies conducted on the ion-pairs containing PF6-, again, indicates the same trend of capability forming H-bonding, major field of these NR3H+ > PyH+>Im+. Within the ammonium ion series, the tendency for H-bond formation obtained is NH4+ > NR3H+ > NR2H2+NRH3+.
The calculated shielding constants of fluorine and phosphorous manifest that both 19F and 31P (I=1/2 for either nucleus) NMR are promising spectroscopic tool for probe of H-bonding since these isotopes not only possess high gyromagnetic ratio but also natural abundance (100%). The electric field gradient of the boron atom changes with hydrogen-bond formation, indicating a non-zero quadrupole coupling constant, , for boron. Therefore, measurements the values of for 11B through nuclear quadrupole resonance spectroscopy provide another available technique for similar studies.
Analysis of the magnitudes of E(2) in the fluoromethanes reveal that the degree of negative hyperconjugation (NHC) increases with increasing number of fluorine substitution. This observation is consistent with the trend reported in literature acquired theoretically or experimentally. Employing values of calculated E(2), we have found that NHC can account for the B-F bond strength in the BFnH4-n series. Futhermore, the concept of NHC can be applied for rationalizing the lower negative charge of the F-atoms than expected as compared to those on F-atoms in PF6- anion. We also propose that the NHC effect in BF4- plays an important role for reducing its ability in forming H-bonding with cations under this study.
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校內：2004-08-08公開校外：2004-08-08公開