在LCBO-MO理論方法的NBO計算中，監測BnF3n-1+ (n=2~5) 簇合物中之硼原子與外接BF3分子中的氟原子間鍵結之作用力。我們發現到與簇合物聚集的驅動力為Lewis酸鹼作用，且以E(2)值來衡量此作用力:LP(F) →LP*(B)，發現隨著團簇大小遞增，E(2)值會隨之減弱，此結果可解釋文獻中呈現的質譜圖並說明此類團簇的大小是受到限制的。數據顯示，BF3-BF2+的E(2)值最大( 137.6 kcal/mol )，若再增加一個BF3分子，則E(2)值就大幅下降( 97.26 kcal/mol )，一直到BF3-B4F11+其E(2)值降為4.58 kcal/mol。此外，由分析其相對應之結合能及電荷數據亦可得到相同的結論。

　　第二部份，我們又以NBO方法計算ClNO3此一分子，從所有異構物中我們計算出以ClONO2之Cs對稱性結構最穩定。且經由天然鍵性軌域間的交互作用情形中發現，此類分子內存在許多穩定的〝非定域化能量〞，其中負超共軛效應扮演極為重要的角色，其次還有一些電子不定域化的作用存在，由於有這些電子不定域化的現象存在，使得此分子能穩定存在在平流層中進行反應。此外，由NBO之donor-acceptor作用分析及構型能量分析，都發現氯原子很明顯有參與負超共軛效應，藉由此結果可提供給研究負超共軛學者們一個極有價值的參考。

　　In order to probe the driving force for formation of BnF3n-1+(n=2~5) ionic cluster from reactions of smaller (n=1~4) clusters with BF3, we have analyzed the donor-acceptor interaction energy, E(2). This is accomplished by LCBO-MO calculations, in which the Weinhold’s natural bond orbitals (NBO) approach was employed. Based on the NBO results, this type of aggregation may be as Lewis
acid-base reaction and hence the extent of the interaction can be quantized by calculated magnitudes of E(2). The results reveal that the major force for the aggregation is ascribed to LP(F)  LP*(B) donor-acceptor interaction. More importantly the values of E(2) decreases uniformly from 138 kcal/mol (n=1) to 5 kcal/mol (n=4). This tendency can therefore be employed to account for the reduced stabilities, as n increases, found in MS spectroscopy.

　　In the second part of this research, the NBO calculations have been carried out on various isomers of ClNO3. The most stable isomer found on the basis of HF energy is ClONO2 of Cs symmetry. Through NBO results it is seen that there are three major types of electron delocalization: LP(O)  Ryd*(N), LP(O)  BD*(NO), and LP(Cl)  BD*(NO). The latter two types are well-known as negative hyperconjugation (NHC) effects. It is considerably instructive that participation of NHC of the chlorine atom has been found in the present study. This conclusion has been further confirmed by analysis of conformation energies. We believe the effects of NHC on the stabilization of ClONO2 would provide a novel molecule for researchers interested in hyperconjugation.

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