吡啶与HCl和CHCl3形成分子间红移氢键和蓝移氢键的理论研究

采用量子化学从头算的MP2方法, 分别在6-31G(d,p), 6-311+G(d,p)和AUG-cc-pVDZ基组下, 研究了复合物C5H5N…HCl(1), C5H5N…HCCl3(2)和C5H5N…HCCl3(3)的分子间氢键. 计算结果表明, 在复合物1中, HCl中Cl—H键伸长, 形成Cl—H…N红移氢键; 在复合物2中, HCCl3中C—H键伸长, 形成C—H…N 红移氢键; 在复合物3中, HCCl3中C—H键收缩, 形成C—H…π蓝移氢键. 自然键轨道(NBO)分析表明, 影响氢键红移和氢键蓝移主要有3个因素: n(Y)→σ*(X—H)超共轭作用、X—H键轨道再杂化和质子供体电子密度重排. 其中, 超共轭作用属于键伸长效应, 电子密度重排和轨道再杂化属于键收缩效应. 在复合物1和2中, 由于键伸长效应处于优势地位导致形成红移氢键; 在复合物3中, 由于键收缩效应处于优势地位导致形成蓝移氢键.

Theoretical Study on Red and Blue Shifting Hydrogen Bonding Between Pyridine and HCl, CHCl3

Ab initio quantum mechanics method(MP2) is employed to investigate intermolecular interactions in the complexes of C5H5N…HCl(1), C5H5N…HCCl3(2) and C5H5N HCCl3(3) at the 6-31G(d,p), 6-311+G(d,p), aug-cc-pVDZ basis sets. For compounds 1 and 2, Cl—H…N(C—H…N) red shifting H-bond is formed with Cl—H(C—H) bond elongation and a concomitant red shift of the corresponding IR stretching frequency. However, for compound 3, C—H…π blue shifting H-bond is formed with C—H bond contraction and concomitant blue shift of the corresponding IR stretching frequency. It is indicated that both Cl—H and C—H stretch increases in intensity and broadens in the spectral band on formation of compounds. It is concluded that a negative permanent dipole moment derivative of the proton donor is not a necessary condition for the formation of the blue shifting hydrogen bond. The NBO analysis shows that the X—H bond length in X—H…Y is controlled by a balance of three main factors. X—H bond lengthening due to n(Y)→σ*(X—H) hyperconjugative interaction is balanced by X—H bond shortening due to increase of s-character and polarization of the X—H bond and redistribution of electron density in proton donor. In compounds 1 and 2, hyperconjugative interaction dominates which results in red shifting H-bonds. In compound 3, the condition is reverse which results in blue shifting H-bonds.