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采用密度泛函理论的B3LYP交换关联能泛函,在6-311+G(2df,2p)基组水平上,对尿嘧啶及硫尿嘧啶分子进行优化计算,发现硫尿嘧啶两个互变异构体中,硫取代7位置氧(U7S)的总能量为-20080.0636eV,硫取代3位置氧(U3S)的总能量为-20079.9896eV,U7S的总能量较小,较为稳定.在同样基组水平上对这些分子进行振动频率分析,发现尿嘧啶分子C—O健伸缩振动频率约为1770cm-1,而形成硫尿嘧啶时,与之相对应的S—O键伸缩振动频率约为1160cm-1,发生了约600cm-1的红移,且红外活性减弱.对应于该振动模式的力常数从16N·cm-1降低至3N·cm-1,折合质量由8amu降至3.8amu,力常数的减弱是产生这一振动红移的主要原因.
Based on the B3LYP exchange-related functional theory of density functional theory (DFT), the uracil and thiouracil molecules were optimized at 6-311 + G (2df, 2p) basis and found that two mutual variations of thiouracil The total energy of sulfur substituted for 7th position oxygen (U7S) is -20080.0636eV, the total energy of sulfur substituted for 3th position oxygen (U3S) is -20079.9896eV, the total energy of U7S is small and stable, and in the same basic group Vibrational frequency analysis of these molecules shows that the frequency of C-O stretching vibration of uracil molecule is about 1770cm-1, while the formation of thiouracil, corresponding to the S-O stretching vibration frequency of about 1160cm- 1, a red shift of about 600cm-1 occurred, and the infrared activity weakened.According to the vibrational mode, the force constant decreased from 16N · cm-1 to 3N · cm-1, the equivalent mass decreased from 8amu to 3.8amu, The weakening is the main reason for the redshift of this vibration.