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.
黎安勇, 闫秀花, 王素纹. 三接触弯曲构型的蓝移氢键CH3…Y的理论研究[J]. 化学学报, 2007, 65(24): 2809-2816.
LI An-Yong*; YAN Xiu-Hua; WANG Su-Wen. Theoretical Study of the CH3…Y Trifurcated Blue-Shifted Hydrogen Bonds. Acta Chimica Sinica, 2007, 65(24): 2809-2816.