丙酮C=O键在溶剂中频移变化的几种理论模型比较

测量了丙酮在16种溶剂中C=O键的伸缩振动拉曼光谱,并且在Gaussian03程序下采用自恰反应场方法(SCRF)对丙酮在各种溶剂中的拉曼光谱进行了理论计算.用三种溶剂模型的电子给体-受体模型、Kirkwood模型和自恰反应场模型对实验结果进行了分析比较,结果表明Gutmann提出的电子给体-受体模型与实验结果符合的最好,而自恰反应场理论结果要好于Kirkwood模型.通过对三种模型的机理进行分析,得出给体一受体模型在解释电负性比较强的分子键振动光谱比较好,自恰反应场模型不但考虑了介电常数ε,而且考虑了分子大小、构型等因素的影响,模型复杂,计算量比较大,但是因为考虑的因素比较多,所以与实验结果也符合的比较好,而Kirkwood模型的主要参数为ε,模型简单,计算简便,能大致反映频移的趋势,说明介电常数是影响频移的一个主要因素.

Explanation of C=O of Acetone Changing in Solvents by Some Models

Raman spectra of acetone's carbonyl stretching in 16 solvents were measured, and were also calculated by self-consistent reaction field (SCRF) method in Gaussian03. The frequency shift in experiment was analyzed by donor-acceptor model, Kirkwood model and SCRF model respectively. Among them, the donor-acceptor model can explain the shift very well. The SCRF method can do it also, while not as well as the donor-acceptor model, but is better than Kirkwood model. Correlating the mechanisms of the 3 methods, it was found that the donor-acceptor model is powerful in explaining the vibrational spectra of molecular bond, which is nucleophilic reagent. The SCRF model considers not only the influence of dielectric constant epsilon, but also the influence of the bulk and the structure of molecule etc. Although the model is complex and difficult to calculate, but it takes many factors into account, so the calculated results accord with experiment better than the Kirkwood model. The main parameter of the Kirkwood model is epsilon, so it is very simple and easy to calculate, nonetheless the trend of frequency shift can still be reflected, indicating that the dielectric constant epsilon is a main character affecting the frequency shift.