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化学学报
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化学学报 ›› 2007, Vol. 65 ›› Issue (24): 2809-2816. 上一篇    下一篇

研究论文

三接触弯曲构型的蓝移氢键CH3…Y的理论研究

黎安勇*, 闫秀花, 王素纹   

  1. (西南大学化学化工学院 重庆 400715)
  • 投稿日期:2007-04-09 修回日期:2007-07-19 发布日期:2007-12-28
  • 通讯作者: 黎安勇

Theoretical Study of the CH3…Y Trifurcated Blue-Shifted Hydrogen Bonds

LI An-Yong*; YAN Xiu-Hua; WANG Su-Wen   

  1. (School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715)
  • Received:2007-04-09 Revised:2007-07-19 Published:2007-12-28
  • Contact: LI An-Yong

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运用量子化学从头算方法, 在MP2/6-311＋＋G(d,p), MP2/6-311＋＋G(2df,2p), MP2/6-311＋＋G(3df,3pd)和QCISD/6-311＋＋G(d,p)水平上, 研究了CH3F, CH3Cl和CH3Br作为质子给体与Cl－, Br－作为质子接受体形成的氢键CH3…Y. 计算结果表明: 6种复合物中C—H键收缩, 伸缩振动频率增大, 形成蓝移氢键. 分子中原子(Atoms in Molecules, AIM)分析表明, 这些复合物的电子密度拓扑性质与普通氢键有着本质的不同, 在Y…H之间不存在键临界点, 而在Y与C之间存在键临界点, 因此这些相互作用严格地不能称为氢键. 自然键轨道(Natural bond orbital, NBO)分析表明, 在这些复合物中弯曲的CH…Y的特殊结构使得分子间超共轭n(Y)®σ*(C—H)减小到可以忽略; 质子接受体的电子密度没有转移到σ*(C—H)上, 而是转移到了σ*(C—X) (X＝F, Cl, Br)上; 存在一定程度的重杂化; 分子内超共轭相互作用减小使得σ*(C—H)的电子密度减少. 这些因素共同导致C—H伸缩振动频率的蓝移.

关键词: CH3…Y弯曲氢键, 蓝移氢键, 电子密度拓扑分析, 自然键轨道分析

Ab initio quantum mechanics methods were applied to investigate the CH3…Y bend hydrogen bonds in the complexes Cl－…CH3F, Cl－…CH3Cl, Cl－…CH3Br, Br－…CH3F, Br－…CH3Cl and Br－…CH3Br. The MP2 level of theory with the four basis sets 6-311＋＋G(d,p), 6-311＋＋G(2df,2p), 6-311＋＋G(3df,3pd) and QCISD/6-311＋＋G(d,p) and the standard gradient technique were used to optimize the geometries and analyze vibrational frequencies. The results show that there are three C—H…Y (Y＝Cl－, Br－) hydrogen bonds in each of the six complexes, and the C—H bond contracts with a concomitant blue shift of the corresponding stretching frequency. The natural bond orbital (NBO) analysis shows that four factors lead to the formation of these blue-shifted H-bonds: (a) intermolecular hyperconjugation in a bend H-bond configuration is very small and can be neglected; (b) there exists rehybridization; (c) the electron density in the Cl－ or Br－ lone pair is transferred not to σ*(C—H) but to the σ*(C—X) (X＝F, Cl, Br) antibonding orbital; (d) decrease of intramolecular hyperconjugation leads to decrease of occupancy in σ*(C—H). The analysis using the theory of atoms in molecules (AIM) shows that the topological properties of electron density for these trifurcated bent H-bonds have essential differences from those of usual H-bonds, where the bond critical point is not between H and Y, but between C and Y.

Key words: CH3…Y bend hydrogen bond, blue-shifted H-bond, electron density topology, natural bond orbital