2,5-二(4-甲基苯基)-1,3,4-噁二唑分子的光谱与热力学性质的理论研究

Theoretical Study of the Molecular Spectra and Thermodynamic Properties of 2,5-Bis(4-methylpheny)-1,3,4-oxadiazole

采用密度泛函理论,在B3LYP/6-31+G*水平计算研究2,5-二(4-甲基苯基)-1,3,4-噁二唑分子的几何结构、光谱、热力学性质.结果显示,该分子三个环处于同一平面,与晶体结构一致.气相中最低能量跃迁吸收峰出现在315 nm,对应最高占据分子轨道到最低未占分子轨道的π-π*电子跃迁.热力学计算显示,随温度的升高,2,5-二(4-甲基苯基)-1,3,4-噁二唑分子的标准摩尔焓Hm,标准摩尔热容Cpm,标准摩尔熵Sm均呈二次函数增大.298.15K与标准大气压下,其标准摩尔生成焓和标准摩尔生成自由能分别为-102.51 kJ/mol和110.88 kJ/mol.表明由稳定单质生成气态2,5-二(4-甲基苯基)-1,3,4-噁二唑分子时尽管要放热,但不能自发进行.

By calculation of the title compound molecules, the geometric structure, spectra and thermodynamic properties of 2,5-Bis （4-methylpheny）- 1,3,4-Oxadiazole molecule were investigated at B3LYP/6-31 ＋ G＊ level by applying the density functional theory. The result showed that the three rings of the said molecule were coplanar, which is consistent with the crystal structure. In gas phase, the absorption peak of the lowest energy transition detected was at 315 nm, corresponding to the electron transition of π-π＊ from HOMO to LUMO. Thermodynamic calculations showed that, with temperature rise, the standard molar enthalpy, standard molar heat capacity and standard molar entropy of the title compound molecule underwent an increase characerized by a quadratic function. The standard molar enthalpy and standard molar free energy were -102.51 kJ/mol and 110.88 kJ/mol under standard atmospheric pressure and 298. 15 K, respectively. The finding indicate that although heat relaesse exists in the process for a stable element being transformed into a tilte compound, the release is not all spontaneous.