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Theoretical calculation of enthalpy of formation of multiconformational molecules: 1,2-ethanediol, propanediols, and glycerol
Chemical Physics Letters ( IF 2.8 ) Pub Date : 2018-03-15 , DOI: 10.1016/j.cplett.2018.03.029
Olga V. Dorofeeva , Taisiya A. Suchkova

The gas-phase enthalpies of formation of four molecules with high flexibility, which leads to the existence of a large number of low-energy conformers, were calculated with the G4 method to see whether the lowest energy conformer is sufficient to achieve high accuracy in the computed values. The calculated values were in good agreement with the experiment, whereas adding the correction for conformer distribution makes the agreement worse. The reason for this effect is a large anharmonicity of low-frequency torsional motions, which is ignored in the calculation of ZPVE and thermal enthalpy. It was shown that the approximate correction for anharmonicity estimated using a free rotor model is of very similar magnitude compared with the conformer correction but has the opposite sign, and thus almost fully compensates for it. Therefore, the common practice of adding only the conformer correction is not without problems.



中文翻译:

多构象分子形成焓的理论计算:1,2-乙二醇,丙二醇和甘油

用G4方法计算了形成四个具有高柔韧性的分子的气相焓,从而导致存在大量低能构象体,以了解最低能构象体是否足以在原子吸收光谱中实现高精度。计算值。计算值与实验良好吻合,而增加对构象异构体分布的校正则使吻合度更差。产生这种影响的原因是低频扭转运动的非谐性很大,在ZPVE和热焓的计算中忽略了这一点。结果表明,使用自由转子模型估算出的非谐性近似校正与保形校正相比具有非常相似的幅度,但是符号相反,因此几乎可以完全补偿。所以,

更新日期:2018-03-16
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