在LCBO-MO理論方法的NBO計算中，獲取鍵能、S成份特性和軌域作用能(即E(2)值)等資料，被用來監測F原子取代對C-Cl鍵的影響效應。計算結果呈現出:由於F原子引進，使C-Cl鍵增強約25kcal/mol。另外所有F原子取代的分子，亦使C-Cl.鍵的S-成份特性具有一致性的增加。使用HF/6-31G*方法計算得到的鍵長和上述觀察的C-Cl鍵能和S-成分兩者結果是有一致性的傾向。這相同的研究方式亦使用在C-F鍵和C-Br鍵，顯示出隨F原子取代造成這些鍵的增強，而鍵強度大小傾向為C-F>>C-Cl~C-Br，可以藉由E(2)值得到合理的相關性。換句話說，在donor-acceptor的lp(F)σ*C-X軌域作用力中，在能量與方向兩方面則特別眷顧σ*c-x軌域。
NBO方法也提供在HCFC化合物中，鍵強度相對大小C-F>C-H>C-Cl，與文獻報導具有一致性的結果。更重要的，在兩個碳系統中，所有構形(comformation)中是以交錯型(gauch form)的能量最低，這結果可以在交錯型時軌域作用能為最大來解釋，這個觀察提供更進一步地證明Weinhld的論點：關於交錯構型穩定性的理由。

The bond energies, s-character, and the orbital interaction energies, E(2), obtained from the NBO method in the LCBO-MO approach have been employed to monitor the effects of fluorine-substitution on the C-Cl bond. Calculated results indicate that the C-Cl bond is strengthened by ~25kcal/mol due to introduction of the F-atom. Besides, the s-characters of the C-Cl bond orbitals in all fluorine-substituted molecules are uniformly increased. Both observations are consistent with the calculated bond distances by the HF/6-31G* method. The same studies performed on C-F and C-Br bonds reveal that these bonds are both strengthened by fluorine-substitution. The extent of bond strengthening is in the trend C-F >> C-Cl ~ C-Br, which can be rationalized by the values of E(2). In other words, the lp(F)→σ*C-X donor-acceptor interaction is most favored for C-F sigma antibonding orbital in view of both energy and orientation.

The NBO method also provides the relative bond strengths in HCFC compounds, C-F > C-H > C-Cl, which is again in accordance with results reported in literatures. More significantly, the lowest-energy conformation in two-carbon system are all dominated by the gauch form. This can be explained by the maximal orbital interaction energy found in this conformation. This observation supplies further evidence in support of the Weinhold’s argument concerning the stabilization of gauch conformation.

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