臺灣博碩士論文加值系統

利用B3LYP/6-31G＊計算去質子的X-C6H4COOH及X-C6H4NH(CH3)2+結構。由NBO分析所得到的最佳化路易士結構顯示，C6H5COOH苯基上有三個共軛雙鍵及羰基(COOH基)穩定電子，脫氫前後分子的總能及穩定度會改變；而在接上取代基後X-C6H4COOH及X-C6H4NH(CH3)2+，其總能及穩定度大小，會受到取代基及取代基取代的位置(鄰位、間位、對位)所影響，其總能、酸度、pka值、鍵長、E(2)值、電荷及s-character百分比均會有改變，特別在脫氫後穩定負電荷的因素，在取代基、取代基取代位置、苯環共振效應、超共軛及負超共軛穩定作用是非常重要的因素。
當取代基氟原子的數目愈多時其穩定度愈高，在取代基氟原子的數目相同時，直鏈取代的穩定度高於支鏈取代，且取代基上含氫氧基比氟原子對穩定度的貢獻更大，取代基上不同取代位置影響穩定度，幾乎是對位取代>間位取代>鄰位取代。利用理論計算所得苯甲酸及二甲苯胺衍生物Isodesmic Reaction的DEreaction值，對Sheppard的實驗結果pkawater ethanol值作圖，有很好的線性關係，此乃表示DE0值愈小，其化合物較穩定，酸度也愈高。苯甲酸羰基的穩定度影響酸度，而穩定度由取代基、取代基取代位置及負電荷決定。取代基的誘導效應、共振效應、超共軛、＋R character及p-π interaction都會影響到分子的穩定度。

B3LYP/6-31G* calculations have been employed to optimize two series of compounds: X-C6H4COOH and X-C6H4NH(Me)2+ {X=CF3，C2F5, n-C3F7, iso-C3F7, n-C4F9, C(OH)(CF3)2}, followed by Natural Bond Orbital studies. Deprotonated counterparts have also been under studies in order to acquire for supplementary and/or comparative information concerning effects (1) the nature of X and (2) the substitution sites of X on acidity. It is also our goal to probe how valid the hyperconjugation argument can account for the substitution effects of X on the acidity of the two series of compounds.
In the fluorinated alkyl substituents, the number of F-atoms will uniformly lead to higher stabilization energies, an observation predicted by hyperconjugation effects.
The site effects generally follow the order para > meta > ortho, which is also well rationalized by the combination of hyperconjugation with the well-known mesomeric effects. The latter contains +R character and p-p interaction between X and the phenyl system. It is also found, for the CnF2n+1 substituents, branched alkyl groups exert fewer enhancements on the acidity than the non-branched.
Moreover, the OH group shows higher enhancements of the acidity than the F-atom does. The relative acidities are well contrasted to the isodemic reaction energies: a more negative isodemic energy results in a more stable product-system, which in return accompanied by a lower reported pKa value.

摘要………………………………………………………………………… Ⅰ
ABSTRACT………………………………………………………………… Ⅱ
誌謝………………………………………………………………………… Ⅲ
目錄………………………………………………………………………… Ⅴ
表目錄……………………………………………………………………… Ⅷ
圖目錄……………………………………………………………………… Ⅹ
重要的專有名詞及其中文譯名…………………………………………… ⅩⅡ
第一章 緒論……………………………………………………………… 1
第二章 理論背景………………………………………………………… 4
2-1、苯甲酸及二甲苯胺簡介…………………………………………… 4
2-2、共振、超共軛、負超共軛………………………………………… 6
2-2-1 共振…………………………………………………………… 6
2-2-2 超共軛………………………………………………………… 8
2-2-3 誘導效應及共振效應………………………………………… 8
2-2-4 負超共軛……………………………………………………… 10
2-2-5 以分子軌域的觀點來說明負超共軛現象…………………… 13
2-3、pKa值………………………………………………………………… 15
2-4、Hammett substituent constants ………………………………… 18
2-5、Bent's rule…………………………………………………………… 19
2-6、+R character………………………………………….…………… 20
2-7、計算原理……………………………………………………………… 21
2-7-1 基底集合……………………………………………………… 21
2-7-2 密度泛函理論(Density Functional Theory)……………… 22
2-7-3 天然鍵結軌域（NBO）………………………………………… 25
第三章 計算方法…………………………………………………………… 29
3-1、量子化學計算選用方法…………………………………………… 29
3-2、量子化學選用基底…………………………………………….…… 29
3-3、計算軟體…………………………………………………………… 29
3-4、計算指令…………………………………………………………… 31
第四章 結果與討論………………………………………………………… 32
4-1、能量的探討…………………………………………………………. 32
4-1-1 C6H5COOH脫氫前後總能變化………………………………… 32
4-1-2 脫氫前後取代基對穩定C6H5COOH的影響…………………… 32
4-1-3 取代基上不同取代位置對穩定C6H5COO－的影響…………… 34
4-1-4 C6H5NH(CH3)2+ 脫氫前後總能的變化………………………… 38
4-1-5 脫氫前後取代基對穩定C6H5NH(CH3)2+之影響……………… 40
4-1-6 取代基對 X-C6H4COO-酸度的影響…………………………… 43
4-1-7 Isodesmic Reaction ………………………………………… 43
4-2、E(2)值的探討……………………………………………………… 45
4-2-1 C6H5COOH脫氫前後，架橋碳碳鍵的DA作用…………………… 45
4-2-2 C6H5COOH脫氫前後，COOH基上氧碳鍵的DA作用……………… 46
4-2-3 X-C6H4COOH中架橋碳碳鍵donor到COOH基的E(2)值………… 47
4-2-4 X-C6H4COOH中架橋碳碳鍵donor到苯環的E(2)……………… 48
4-2-5 X-C6H4COOH中COOH基及苯環donor到架橋碳碳鍵的E(2)值… 49
4-2-6 X-C6H4COO-中架橋碳碳鍵donor到苯環的E(2)值…………… 50
4-3、負超共軛E(2)值的探討……………………………………………… 51
4-3-1 C6H5COOH脫氫前後LP的不定域化作用………………………… 51
4-3-2 X-C6H4COOH中COOH基上LP的不定域化作用…………………… 53
4-3-3 X-C6H4COO-中COOH基上LP的不定域化作用…………………… 55
4-3-4 X-C6H4COO-中苯環上LP的不定域化作用……………………… 56
4-3-5 X-C6H4COOH中取代基上氟的LP的不定域化作用……………… 57
4-3-6 X-C6H4COO-中取代基上氟的LP的不定域化作用……………… 58
4-4、鍵長的探討…………………………………………………………… 59
4-4-1 C6H5COOH脫氫前後的鍵長……………………………………… 59
4-4-2 X-C6H4COOH中O-H鍵鍵長的變化……………………………… 61
4-4-3 X-C6H4COOH中C=O鍵鍵長的變化……………………………… 63
4-4-4 X-C6H4COOH中C-C鍵鍵長的變化……………………………… 65
4-5、C6H5COOH電荷的探討………………………………………………… 68
4-5-1 C6H5COOH脫氫前後碳的電荷變化……………………………… 68
4-5-2 X-C6H4COOH脫氫前後電荷的變化……………………………… 68
4-5-3 X-C6H4COOH各取代基位置不同電荷的變化…………………… 71
4-5-4 X-C6H4COO－取代前後電荷的變化…………………………… 72
4-5-5 X-C6H4COO－各取代基位置不同電荷的變化………………… 73
4-6、C6H5COOH鍵結軌域(Bond orbital)的探討………………………… 75
4-6-1 COOH基上O-H鍵上氧的s-character…………………………… 75
4-6-2 COOH基上O-H鍵上氧的s-character與O-H鍵的鍵長………… 78
4-6-3 COOH基上架橋碳與O-H鍵上氧的s-character………………… 78
第五章 結論…………………………………………………………………… 79
參考文獻……………………………………………………………………… 140

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