異腈与羟基形成氢鍵的研究——Ⅱ.共价成鍵作用的計算

HYDROGEN BOND FORMATION BETWEEN THE CARBON ATOM OF ISONITRILE AND THE HYDROXYL COMPOUNDS——Ⅱ. EVALUATION OF THE COVALENT CONTRIBUTION

将O—H…:C体系近似地看成四电子体系用价鍵法計算了这个氢鍵体系的“离位能”。取下列三个“价鍵式”波函数的綫性組合作为四电子体系的波函数:积分H_(μμ),H_(μν)的值用Coulson及Danielsson所建議的半經验法估計。計算了在L(O—H…:C)=2.80,L(O—O)=0.99时,体系O—H…:C的离位能为8.0仟卡。将这个值与O—H…:O体系的离位能6.8千卡(Coulson及Danielsson的估計)对比,可以得出結論:異腈的碳原子由于具有独对电子可以作为質子接受体形成氢鍵。

The O—H…: C system is approximately considered as a four electron system. Using valence-bond method, the delocalization energy of this H bond system was calculated. The wave function of the four electron system was takon as a linear combination of the following three valence bond wave functions: (Ⅰ) (?)-H:C≡ψ_1 (Ⅱ) (?) (?):C≡ψ_2 (Ⅲ) (?) H——^+C≡ψ_3 ψ=c_1ψ_1+c_2ψ_2+c_3ψ_3 The H_(μμ) and H_(μν) integrals were calculated by the semi-empirical method proposed by Coulson and Danielsson. The delocalization energy of the hydrogen bond system O—H…:C was calculated for L (O—H…:C)=2.80 A and L(O—H)=0.99(?) to be 8.0 Kcal. This value may be compared to the delocalization energy of O—H…:O system, which is estimated to be 6.8 Kcal by Coulson and Danilsson. From the above consideration, we may conclude that isonitrile may act as a proton acceptor in a hydrogen bond system owing to the presence of lone pair electrons.