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熵是化合物的重要热力学函数之一,最近有人对此作了改进性计算。计算依据主要取自热力学、光谱学实验数据(如比热、振动频率和转动光谱常数)。对于一些不稳定的反应中间体,尤其是过渡态,上述实验几乎无法进行,熵的实验数据很难获得。Benson等人曾提出过渡态熵的估计方法,但不是纯理论性的。我们利用量子化学对反应体系势能面的研究成果,获得过渡态的谐振动频率、鞍点几何构型,从理论上探讨了过渡态熵的计算。据统计力学,过渡态熵可表示为:
Entropy is one of the important thermodynamic functions of compounds. Recently, some people have made some improvement calculations. Calculations are based on thermodynamic and spectroscopic experimental data (such as specific heat, vibrational frequency, and rotational spectral constants). For some unstable reaction intermediates, especially the transition state, the above experiment is almost impossible, the entropy experimental data is difficult to obtain. Benson et al. Proposed a method of estimating entropy of transition states, but this is not purely theoretical. We use quantum chemistry on the potential energy of the reaction system research results, access to the harmonic state of the resonant frequency and saddle point geometry, the theoretical calculation of the transition state entropy. According to statistical mechanics, transition state entropy can be expressed as: