Ab Initio MP2 and DFT Study of the Thermal Syn Elimination Reaction in Ethyl Formate

The thermal elimination reaction that appears in some polycarbonates has been studied by density functional theory (DFT) and ab initio methods of different levels. This work has been focused in the elimination process of ethyl formate, as a good model of this kind of reaction. Different minima and the transition state have been found to characterize the thermal elimination reaction, and the activation energy has been obtained. In this study, we have used different methods to calculate the contribution of the correlation energy; different basis sets were also employed. This will allow us to perform an analysis of the influence of the applied method in the obtained results to study the thermal elimination. The lengthening of the bonds has also been analyzed to shown how concerted the thermal elimination is in the ethyl formate. Three minima have been found for the ethyl formate, two of them are very close and the third is higher in energy. In general, the DFT method with a B3LYP functional gives a less concerted reaction. A nonplanar transition state is predicted by most of the methods used.

通过密度泛函理论（DFT）和不同水平的从头算方法研究了一些聚碳酸酯中出现的热消除反应。这项工作重点关注甲酸乙酯的消除过程，将其作为这类反应的一个良好模型。已经发现不同的极小值和过渡态可用于表征热消除反应，并获得了活化能。在本研究中，我们使用了不同的方法来计算相关能的贡献，还采用了不同的基组。这将使我们能够分析所应用的方法对研究热消除所获得的结果的影响。还分析了键长的变化，以表明甲酸乙酯中的热消除协同程度如何。已发现甲酸乙酯有三个极小值，其中两个非常接近，第三个能量较高。一般来说，采用B3LYP泛函的DFT方法给出的反应协同性较差。大多数所使用的方法都预测了一个非平面的过渡态。