摘 要 為了探討水溶液中Diels - Alder反應反應速率大幅 提昇的原因,我們以Diene加成到Dienophile上所新生成鍵結的鍵長變化 量,來定義Diels - Alder反應的反應坐標,並將溶液中的反應,區分為 反應中心與溶劑兩部分。本研究是以量子計算方法,首先計算在沒有溶劑 存在狀態下,Diels - Alder反應的反應過程。經由鍵序與S - character 的分析發現,我們對反應坐標的定義是合理的,而生成熱位能曲線與硬度 曲線的變化也具一致性。接著再以分子模擬的方法( MD ),探討溶劑效應 對Diels - Alder反應的影響。根據徑向分佈函數與量子計算的結果顯示 ,氫鍵效應對於加速純水中Diels - Alder反應的影響,應該考慮下述問 題:氫鍵效應對於加速純水中Diels - Alder反應的貢獻,應隨著反應物 之氫鍵接受者受水分子極化的位置,距離新生成碳-碳鍵的遠近,而有大 小之分;距離愈遠貢獻愈小,距離愈近貢獻愈大。此外,對於反應物結構 易受氫鍵效應極化的分子組合,亦須考慮偶極-偶極作用力對於純水中 Diels-Alder反應的加速影響。最後,根據自由能微擾法( FEP )計算發現 ,溶劑的疏水性效應確為影響Acridizinium cation與Cyclopentadiene於 純水中Diels-Alder反應加速的主因。另外,根據量子計算加上FEP的方法 ,對於Acridizinium cation與Cyclopentadiene在純水中的Diels - Alder反應,其模擬計算的反應活化能與實驗結果相當吻合。 In order to explore the reasons thatthe Diels - Alder reactions be accelerating in water , we de fine the reaction coordinatewhic h is the of the lengths of the t wo forming C-C bonds when the di ene add to the dienophile and se parate reactions in water from r eaction center and solvent . Fir st , our research use quantum me thods to calculate the process w hich is the Diels-Alder reaction s in gas .By bond order and S-ch aracter analysis , wewe find tha t the define of the reaction coo rdinate is reasonable and the cu rve variation for heatof formati on and hardness is consistent , too .Secondly , we use Molecular Dynamic simulations toexplore th e influences of Diels- Alder rea ctions by solvent effect . Accor ding to Radial Distribution Func tion's and quantum calculation's analysis results , the influence s of the hydrogen effect for Die ls-Alder reactions in water , ou r must consider below problems : if the position which the hydro gen acceptor be polarized is far from the position which the new forming C-C bonds , hydrogen-bo ndeffect has smaller assistance for Diels-Alder reactions . Othe rwise , hydrogen effecthas large r one . Besides , if reactants structureis polarized easily by hydrogen effect , it isimportant to consider Dipole-Dipole inter action .Finally , according to t he calculation of FreeEnergy Per turbation ( FEP ) simulations , hydrophobic effect is the major reason which on theacceleration of the Diels-Alder reactions ofA cridizinium cation and Cyclopent adiene in water .Besides , accor ding to quantum calculation and FEP our results of the calculati on is consistent withexperiment results .
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