鄰位硝基甲苯的解離與重排反應與9-芴酮的溶劑效應之量子化學計算研究

Abstract

本論文的第一部份利用密度泛函方法(Density Functional Theory，DFT)以及高精確度方法G2M(cc,MP2)來研究鄰位硝基甲苯(o-nitrotoluene)在氣態下的解離及重排反應。經由提出可能的反應路徑並找到其反應物、產物及過渡態結構，我們得以對其整體反應有一個初步的認識。接下來我們使用DFT以及G2M(cc,MP2)兩種方法對所得的結構進行單點能量計算，以繪製其反應能量曲面，同時對兩種方法所得到的能量作比較及討論。根據計算所得的能量，我們確認了文獻中所觀察到的反應在位能面上確實是較為可能發生的反應。 本論文的第二部份是關於9-芴酮在不同溶劑中展現的溶劑效應。文獻指出，其螢光光譜峰在非質子性溶劑(aprotic solvents)中隨著溶劑的極性增加而產生紅位移，同時在質子性溶劑(protic solvents)中則會產生異常大的紅位移。本研究中使用DFT方法、單電子激發組態交互作用(Configuration Interaction Single excitation, CIS)及完整活化空間自洽場(Complete Active Space Self Consistent Field, ACSSCF)方法取得9-芴酮在基態及激發態的結構，利用含時密度泛函方法(Time Dependent DFT, TDDFT)求得其吸收及螢光波長，並搭配可極化連續體模型(Polarizable Continuum Model, PCM)來處理9-芴酮在非質子性溶劑中的溶劑效應。對於質子性溶劑中的溶劑效應，本研究使用超分子法(supermolecule method, 或稱微溶劑效應)來處理之，並成功解釋了分子間氫鍵對螢光波長所產生的效應。

The first part of the thesis utilizes Density Functional Theory (DFT) and high-accuracy scheme G2M(cc,MP2) to study the dissociation and rearrangement reactions of o-nitrotoluene. We enumerate possible reaction paths, and determine the geometries of reactants, products and transition states. By calculating the single point energies with DFT and G2M(cc,MP2) methods along specific reaction paths, we plot the potential energy surface (PES). Based on these calculations, we identify the reaction pathways connecting to the three experimental observed products. The second part of the thesis studies the solvent effect of 9-fluorenone (9F) in (protic and aprotic) solvents with different polarity. We use DFT, configuration interaction single excitation and complete active space self-consistent field methods to calculate the ground- and excited-state geometries of 9F. We use polarizable continuum model to treat the solvent effect in aprotic solvents. The calculations reproduce the gradual red-shift in fluorescence spectra with increasing polarity of aprotic solvents, observed experimentally. In protic solvents, our results, based on the supermolecule (microsolvation) method, show that intermolecular hydrogen bonding contribute to additional red-shift in spectrum, which is consistent with experimental observations.