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An ab initio computational study of the enhancing role of the methyl group in the M···H (M=S and O) hydrogen bond has been carried out at the QCISD/6-311++G(2df,2p) level. The bond lengths, frequency shifts, and interaction energies were analysed. The methyl group of the electron donor plays a positive role in the formation of the hydrogen bond. Its enhancing role is stronger in the O···H hydrogen bond than in the S···H hydrogen bond. The results show that the methyl group has a prominent effect on the strength of the hydrogen bond. The interaction energy is increased by 347% for the Me2O–HCN complex relative to that for the O–HCN complex. The enhancing mechanism of the methyl group has been analysed by means of natural bond orbital (NBO) theory. The electrostatic interaction is of more importance to the O···H hydrogen bond, whereas dispersion and charge-transfer interactions play a more significant role in the S···H hydrogen bond. 相似文献
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采用密度泛函理论(density functional theory, DFT)中的杂化密度泛函B3LYP方法,在6-311++G**基组水平上对几种取代苯硫酚分子的构型进行了几何优化,得出了它们的最稳定构型并对其能级差、核独立化学位移、极化率和振动光谱进行了理论计算。研究结果表明,4-巯基吡啶(4-MPY)、4-巯基苯甲酸(4-MBA)和4-巯基苯胺(PATP)均为平面构型,1,4对巯基苯(BDT)中S-H键与苯环平面的夹角为20.2°,4-甲基巯基苯(4-MBT)中S-H键与苯环平面的夹角为39.6°。几种分子都具有很强的芳香性和较大的极化率值。5种分子的极化率张量平均值大小顺序为BDT>4-MBT>4-MBA>4-MPY>PATP,极化率的各向异性不变量变化趋势为4-MBA>4-MBT>BDT>PATP>4-MPY。 相似文献
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CHENG Jian-bo Lǚ Jia-ping GONG Bao-an LI Wen-zuo 《高等学校化学研究》2007,23(4):469-473
The optimized molecular structure and harmonic vibrational frequencies of a 1,4-bis[2-(4-pyridyl)ethenyl]-benzene(BPENB)molecule were calculated via five popular density functional theory(DFT)methods.On the basis of the comparison between calculated and experimental results,it is concluded that the B3PW91 and B3LYP methods are superior to the others in optimizing structures,and the BPW91 method reproduces the observed fundamental frequencies most satisfactorily. 相似文献
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