乙醛二聚体内蓝移型氢键的理论研究

利用理论方法研究了乙醛二聚体内的氢键. 在MP2/6-31＋G(d), B3LYP/6-31＋G(d), B3LYP/6-311＋＋G(d,p)和B3LYP/6-311＋＋G(3df,2p)水平上, 利用常规方法和均衡校正方法对3种稳定的乙醛二聚体进行了几何优化和振动频率计算. 计算结果表明: 在二聚体A和C中乙醛中C—H键强烈收缩, 存在显著的C—H…O蓝移型氢键. 自然键轨道(NBO)分析表明, 电子供体轨道和电子受体轨道之间相互作用的稳定化能、分子内电子密度重排、轨道再杂化和结构重组是决定氢键红移和蓝移的主要因素. 其中, 轨道间稳定化能属于键伸长效应, 分子内电子密度重排、轨道再杂化和电子受体内部结构重组属于键收缩效应. 在二聚体A和C中, 由于键收缩效应处于优势地位导致C—H…O蓝移氢键存在.

Theoretical Study on Blue-shifted Hydrogen Bonds in CH3CHO Dimers

Theoretical calculations were performed to study the nature of the hydrogen bonds in the CH3CHO dimers. The geometric structures and vibrational frequencies of its three stable dimers at the MP2/6-31＋G(d), B3LYP/6-31＋G(d), B3LYP/6-311＋＋G(d,p) and B3LYP/6-311＋＋G(3df,2p) levels were calculated by standard and counterpoise-corrected methods, respectively. The results indicate that in the dimers A and C the C—H bond is strongly contracted and C—H…O blue-shifted hydrogen bonds were observed. From the natural bond orbital analysis it can be seen that the X—H bond length in the X—H…Y hydrogen bond is controlled by a balance of four main factors in the opposite directions: hyperconjugation, electron density redistribution, rehybridization and structural reorganization. Among them the hyperconjugation has the effect of elongating the X—H bond, but the other three factors belong to the bond shortening effects. In the dimers A and C, the shortening effects dominate which lead to the blue shift of the C—H stretching frequencies.