我們利用Gaussian98軟體，以B3LYP/6-31G＊的方法，去計算甲烷上以鹵素原子取代氫，C－H鍵長的變化；以及當氫鍵接受體靠近時，C－H鍵長的變化。去驗證Weinhold提出該鍵長是由於氫鍵接受體對C－H鍵結的負超共軛及C－H鍵的重新混成所達成平衡下的結果。
在單純鹵烷分子存在下，其鍵長主要是受到C－H鍵中C的s character的因素主宰。當有氫鍵接受體靠近時，在距離尚遠時，C－H鍵長不僅沒有伸長，有的甚至隨著距離的靠近而縮短鍵長，這是由於重新混成的效用超越了負超共軛的影響；當距離靠近到ㄧ定的程度，C－H鍵長急遽的增加，由於負超共軛的影響超越了重新混成的效用。若比較不同的氫鍵接受體，其鍵長主要由氫鍵接受體對C－H鍵結的負超共軛，E(2)值決定，甚至呈線性關係。當氫鍵接受體相同，僅改變氫鍵予體C原子的取代基，發現這對鍵長幾乎不影響；若將中心原子改變，依然與E(2)值呈線性關係，不過受影響的程度不同，中心原子電負度越小者受影響越顯著。

Weinhold and co-workers suggested the X－H bond length in X－H…Y hydrogen bonded complexes is controlled by a balance of two main factors acting in opposite directions. One is n(Y)→σ＊(X－H) hyperconjugative interaction leading to X－H bond lengthening, and the other is rehybridization leading to X－H bond shortening. We concentrate on the C－H bond length of methane substituted by halogens. All computations are performed using Gaussian98 program, and all discussions in this paper are based on B3LYP/6-31＋G＊ calculations.
Without hydrogen bond acceptors, the C－H bond length is mainly affected by s-character of C atom. When hydrogen bond acceptor is present, at larger distance, the C－H bond length shortening is due to the increase in the s-character of the C－H bond, and at shorter distance, the C－H bond length lengthening is due to n(Y)→σ＊(X－H) hyperconjugative interaction. If we change with different hydrogen bond acceptors(Y), the C－H bond length is mainly affected by hyperconjugative interaction. The C－H bond length even has linear relation with E(2). If we use the same hydrogen bond acceptor(Y), the C－H bond length keeps the same in spite of different substitutions on C atom of methane. If we change the central atom, the C－H bond length still has linear relation with E(2), but the slope is different. The larger electronegativity of the central atom is, the smaller the slope is.

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