Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/16210
標題: 乙醯化合物,CH3COR,(R=H,F,Cl,OH,CN,NC,BH2,NH2,CH3)分子內互變異構 現象(Tautomerism)之ab initio分子軌域研究
Theoretical studies on the keto enol intramolecular tautomerism of some acetyl derivatives ,CH3COR,(R=H ,F,Cl,OH,CN,NC,BH2,NH2, CH3)
作者: 吳承倉
Wu, Chen-Chang
關鍵字: keto

enol
tautomerism
nbo
negativ hyperconjugation
烯醇
互變異構
自然鍵結軌域
負超共軛效應
出版社: 化學學系
摘要: 本篇論文係以 ab initio 分子軌域理論計算, 來研究一些乙醯化合物 (CH3CCOR,R=H,F,Cl,OH,CN,NC,BH2,NH2,CH3)的分子內互變異構現象( Tautomerism). 全部的逗留點 (Stationary Point)包括 Keto-form, Enol-form 及 過渡態結構 皆經HF/6-31G* 及 MP2/6-31G*之完全幾何優 選(Full Geometry Optimization), 並經由振動頻率計算予以確認. 為求 得電子相關能量(Electron Correlation Energy) , 吾人更進一步做 MP4/6-311++G**//MP2/6-31G*計算. 此外也利用NBO (Natural Bond Orbital)分析取得分子內各個鍵結的資料, 並利用IRC(Intrinsic Reaction Coordinate)計算來確定 過渡態與 反應物 和 產物 在反應座 標軸上的對應關係.NBO 計算結果顯示, 在Keto-form 時, 分子有超共軛( Hyperconjugation) 效應存在, 並且位於羰基上氧原子的孤電子對(Lone Pair Electrons) 與 C-R 之反鍵結存有強烈作用.例如 R=F 時, 此作用 所產生的穩定能(Stabilization Energy)即高達61.88 Kcal /mole. 相對 的 在Enol-form 時, 電子分別由氧原子和取代基進入 C=C π鍵之反鍵結 軌域, 此作用分別提供了47.53 Kcal/ mole 及30.30 Kcal/mole 的穩定 能. 然而在過渡態時, 氧原子的孤電子對與C1-H7之反鍵結, 亦顯現強烈 的作用存在, 且穩定能高達 152.03 Kcal/mole.由 Enol 轉變成 Keto 之 互變異構的過程中, 當 R=CN 時,能量障礙ΔE值最大:73.81(HF), 57.42(MP2), 56.51(MP4) Kcal /mole; 其最小值發生在 R=NH2 時: 47.75(HF), 38.93(MP2), 39.10(MP4) Kcal/mole .
Ab initio molecular orbital calculations have been performed on the intramolecular tautomerism of some acetylderivatives (CH3 CCOR,R=H,F,Cl,OH, CN,BH2,NH2,NH2,CH3).All stationary points ,the Keto Enol and Transition structures ,were optimized at the HF/6-31G* level and MP2/6-31G* level,and confirmed by the frequency calculations. The intrinsic reaction coordinates were also followed from the TS toward reactants and products. The natural bond orbital (NBO) analysis shows : (Ⅰ) In the Keto_form ,the methyl group of acetyl appears to have the hyperconjugation effect ,except for NH2 , and the lone pair electrons on the Oxygen have strong interaction with the C-R σ* orbital , negative hyperconjugation, (R=F,nO -> σ* C-F, the stabilization energy is 61.88 Kcal/mole). (Ⅱ) In the Enol_form, the lone pair electrons on the Oxygen and substituent will delocalize into C=Cπ* orbital ,(R=F,the stabilization energy of nO -> C=C π* is 47.53 Kcal/mole , nF -> C=C π* is 30.30 Kcal/mole ). (Ⅲ) In the transition state ,the interaction between the lone pair electrons of the Oxygen and σ* is so strong ( R=F,nO -> C-H σ* , that the stabilization energy goes up to 152.03 Kcal/mole). (Ⅳ) Among the tautomerization processes , the highest energy barrier [73.81 Kcal/mole (HF),57.42 Kcal/mole (MP2),56.51 Kcal/mole (MP4)] occurs in R=CN while R=NH2 have the lowest [47.75 Kcal/ mole (HF),38.93 Kcal/mole (MP2),39.10 Kcal/mole (MP4)].
URI: http://hdl.handle.net/11455/16210
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