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研究生： 黃嘉慶
論文名稱： 甲基第三丁基醚及其衍生烷氧自由基氣相反應之理論計算研究
Theoretical Studies of Tropospheric Reactions of Methy tert-Butyl Ether and Its Derivative Alkoxy Radicals
指導教授： 何嘉仁
Ho, Jia-Jen
學位類別： 碩士
Master
系所名稱： 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： 111
中文關鍵詞： 甲基第三丁基醚 、烷氧自由基
英文關鍵詞： Methy tert-Butyl Ether, MTBE, Alkoxy Radicals
論文種類： 學術論文
相關次數： 點閱：169  下載：32 
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    • 本論文藉由理論計算的方法，在B3LYP/6-311++G(d,p) 的計算層級下，探討甲基第三丁基醚(MTBE)與其衍生的烷氧自由基在大氣中的反應，並比較各種反應路徑的能量與特性，再設計各種不同碳數、結構的烷氧自由基，以研究其在大氣中反應的規律性。本文共分為以下三個部分進行研究：
    第一部份 探討MTBE在室溫下與OH自由基反應的理論計算研究，計算結果發現MP2/6-31+G(d)方法所得的數據與實驗值相差較大，而且自旋污染的問題嚴重，用B3LYP/6-311++G(d,p)層級來處理本系統，不但自旋污染的問題得以解決，反應能障也比較符合實驗的數據。OH自由基從MTBE甲氧基位置脫氫與從第三丁基位置脫氫的能障相差不大，主要的產物則為第三丁醇(TBA)、甲醛、異丁烯與甲醇等。
    第二部份 我們對MTBE在空氣中會產生的兩種烷氧自由基(A1及B1) 做了一系列的計算，探討一般烷氧自由基在空氣中的三個主要的反應過程，發現A1與B1的表現並不像一般的烷氧自由基規律，在A1主要進行的是與氧分子的脫氫反應(Oxidation)；而在B1 series則主要進行自身分解(Decomposition)與異構化(Isomerization)反應。造成這些變化的主要因素，則是MTBE上的氧原子。我們也探討了空氣中其他重要的分子對於A1、B1烷氧自由基的反應性，發現除了一般公認的氧分子之外，空氣中的NO分子更能與A1、B1烷氧自由基反應，NO可利用O原子進行脫氫，也可利用N原子形成穩定的中間物，或者更進一步形成產物。
    第三部份 我們完成多種烷氧自由基的分解反應(Decomposition)、氧化反應(Oxidation)與異構化反應(Isomerization)的計算與比較，並探討不同的分子對氧化脫氫反應的影響，並且改變烷氧自由基的結構，加入雙鍵，以計算雙鍵對分解反應的影響。計算的結果發現烷氧自由基的級數以及分解反應產物的能量、結構都能影響分解反應的能障，甚至過渡狀態上的結構與自旋密度也有密切關係。雙鍵的存在不但會影響反應的能障，也會影響斷鍵的選擇性，而且雙鍵的位置不同，有可能使能障大幅降低或提高，更是影響能障的關鍵因素。雙鍵系統的反應能障與反應熱之間，仍然存在著與單鍵系統一樣的線性關係。異構化反應的計算利用NPA電荷分析，推論即使同樣是六圓環的過渡狀態結構，當轉移氫原子的碳上有其他烷基取代時，便能降低其異構化反應的能障。與氧反應對低碳數的烷氧自由基而言是最重要的反應機構，然而在碳數更多的烷氧自由基中，由於立體障礙的影響，使得與氧反應的機率更為困難，六圓環異構化反應便成為最重要的反應途徑了。最後我們用不同的分子來取代氧分子的作用，發現所有烷氧自由基對這些分子的反應性都有相同的趨勢。

    This thesis deals with the calculation of tropospheric reaction of methyl tert-butyl ether (MTBE) and its derivatives by density functional theory at B3LYP/6-311++G(d,p) level. To find the rules of alkoxy radicals in the reaction of atmosphere, we studied several C1-C5 alkoxy radicals of different structures in the reactions and analyzed their relationships. There are three major sections for the reactions we studied and they are rendered here.
    Section 1 We study the hydrogen abstraction reaction with hydroxyl radical and the subsequent rearrangements and fragmentations of MTBE in atmospheric condition. The result of inaccurate energy value and severe spin contamination at MP2/6-31+G(d) level makes us switch to B3LYP/6- 311++G(d,p) level of calculation. There are two possible positions of MTBE that hydroxyl radical can abstract the hydrogen atom and our results indicate that they are competitive, and the final products should be t-butyl alcohol (TBA), formaldehyde, isobutene and methanol, which agree well with the experimental result.
    Section 2 Two derivatives of alkoxy radicals (A1 and B1) are studied in this section. We investigate their decomposition, isomerization and oxidation reactions, which are major reaction processes for general alkoxy radicals in the atmosphere. We conclude that the oxygen atom in MTBE may be a major factor that change the reaction tendency significantly We also investigate A1 and B1 to react with other important molecule in atmosphere such as N2, NO, and CO. The result indicates that NO is more active than O2 toward forming stable intermediates.
    Section 3 There are some good relationships between energy barriers and reaction energies for primary and secondary alkoxy radicals in carrying out decomposition reaction. We also study the unsaturated alkoxy radicals in the decomposition reaction, and find that the position of double bond will affect energy barrier and selectivity significantly. Analogous to the saturated alkoxy radicals, the unsaturated ones also have good linear relationship between energy barriers and reaction energies. The natural population analysis (NPA) in 1,5 H-shift isomerization reaction indicates that alkyl substitution on H-transferred carbon atom could decrease the energy barrier. The oxidation reaction with oxygen is the most important channel in small alkoxy radicals (<C4), in contrast, the isomerization reaction becomes dominant in large alkoxy radicals, partly because of larger steric effect and much smaller isomerization barriers.

    中文摘要 iii 英文摘要 vi 第一章 緒論 1-1簡介 1 1-2 參考文獻 4 第二章 Methyl tert-Butyl Ether 與OH自由基在氣相反應的理論計算研究 2-1 前言 5 2-2 計算方法 6 2-3 結果與討論 8 2-3-1 GEOMETRIES 8 2-3-2 ENERGIES AND POTENTIAL ENERGY SURFACE 17 2-3-3 REARRANGEMENT AND FRAGMENTATION 26 2-4 結論 30 2-5 參考文獻 32 第三章 MTBE衍生烷氧自由基在大氣反應的理論計算研究 3-1 前言 34 3-2 計算方法 38 3-3 結果與討論 38 3-3-1 GEOMETRIES 38 3-3-2 ENERGIES AND POTENTIAL ENERGY SURFACE 46 3-3-3 OXIDATION WITH X (X=O2、N2、CO、NO) 53 3-4 結論 56 3-5 參考文獻 58 第四章 C1-C5烷氧自由基在大氣反應的理論計算研究 4-1 前言 60 4-2 計算方法 63 4-2-1 文獻探討 63 4-2-2 計算方法討論 64 4-3 結果與討論 69 4-3-1 DECOMPOSITION 69 4-3-2 UNSATURATED ALKOXY RADICALS 84 4-4 結論 92 4-5 參考文獻 93 第五章 總結 95

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