The molecular structures, spectra and thermodynamic properties of coumarins a and b were calculated using the density functional theory B3LYP /6-31++G** method.Then, the polarized continuum models (PCM) of Tomasi were used to discuss solvent effects.The computational results showed that for coumarins a and b molecules in gas, the lowest energy absorption wave lengths are 352 and 355 nm, respectively, and the solvents and polarity have few influence on the lowest energy absorption wave lengths of coumarin a.However, the using solvents lead to red shift 7-10 nm for lowest energy absorption wave length of coumarin b and the polarity of solvents has no effect on it.At 298 K, the standard molar enthalpy of formation of coumarins a and b molecules are-1373.171 and-1310.805 kJ/mol, respectively, the t standard molar Gibbs free energy of formation of coumarins a and b molecules are-1064.043 and-1035.849 kJ/mol, respectively, the standard molar entropy of coumarins a and b molecules are 763.910 and 742.150 J·mol-1·K-1, respectively.%使用密度泛函理论方法在B3LYP /6-31++G**理论水平对两种香豆素a和b分子的几何结构、光谱、热力学性质进行理论计算研究,并基于Tomasi的极化统一场模型(PCM)讨论溶剂效应.结果显示,香豆素a和b分子在气相中的最低能量吸收波长分别为352和355 nm,溶剂及其极性大小对香豆素a最低能量吸收波长影响很小,但在溶剂作用下香豆素b分子的最低能量吸收波长红移7-10 nm,溶剂的极性对该波长影响较小.298 K标准压力下香豆素a和b分子的气态标准摩尔生成焓ΔfHΘm分别为-1373.171和-1310.805 kJ·mol-1,标准摩尔生成自由能ΔfGΘm分别为-1064.043和-1035.849 kJ·mol-1,标准摩尔熵SΘm分别为763.910和742.150 J·mol-1·K-1.
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