本論文分兩個部分，在第一部分中主要研究在氣相條件下，我們發現在不飽和的系統下，甲基的CH鍵結軌域會推動HOMO、LUMO能量變化，研究的分子包括了乙烯、苯、萘、吡啶，當分子進行甲基的取代後，藉由計算UV-vis *電子吸收光譜的紅移現象得知其HOMO/LUMO的能隙變得比母分子小是由於甲基化的影響所導致的。簡單地來說，以一個軌域為基礎的解釋就是在量子力學上提出電子光譜的超共軛作用。在第二部分中，超共軛效應藉由甲基透過相同的軌域作用去增加氮原子的電子孤對能量：CHlp(N)，從胍進行甲基取代後變為二甲基胍，lp(N)的能量由-0.30270 eV 降低至-0.25586 eV變得較不穩定，在文獻中提到這個不穩定的變化導致高電子貢獻能力的二甲基胍lp(N) 據有降血糖藥物的作用。在lp(N)的能量基礎上同樣的論證可以去解釋文獻中提到胍的毒性會比雙胍還少：氨基氮的lp(N)能量減少從-0.27882 eV降低至-0.30270 eV。以上兩部分都是研究取代基對邊界軌域(frontier orbital)能量造成的影響，並做波函數的分析，發現取代基具有誘導效應和軌域作用，但以軌域作用較具支配性，而其中的超共軛效應，更扮演很重要的角色，探討其中的差異。本實驗室用理論計算去研究這些現象，能與實驗數據進行比較，也能用於研究分子的合成、調整能隙的大小。

In the course of part one of this investigation, we have found that CH bond orbital(s) of a methyl group would push up both HOMO and LUMO of the unsaturated systems, including ethylene, benzene, pyridine and naphthalene. Therefore, the HOMO/LUMO gap gets smaller than the parent molecules, which accounts for the red-shifts of UV-vis * electronic absorption spectra resulting from methylation. In simple words, an orbital-based explanation has been proposed to understand quantum-mechanically the hyperconjugation effects on electronic spectroscopy. In the second part of this work, the hyperconjugation effects associated with a methyl group would increase the electron lone-pair energy on the nitrogen-atom through the same orbital interactions: CHlp(N). Going from qua to di-gua, The energy of lp(N) is destabilized from -0.30270 eV to -0.25586 eV. This destabilization leads to a higher electron-donating capability of lp(N) in di-gua in treatment of xxx disease reported in literature. The same argument made on the basis of the energy of lp(N) can explain the published results that the toxicity of single-qua would be reduced compared to di-qua: the energy of lp(N) of the amino nitrogen is lowered from -0.27882 to -0.30270 eV.

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