有机含氟化合物在物理及化学性质上与对应的碳氢化合物有较大的差异性。比如多氟取代醇作为溶剂对化学反应的效率、反应速率、阳离子、阴离子以及自由基等中间体的生成均有较大的影响，在促进部分化学反应速率和转化率方面有着显著的作用。因此，在多氟取代醇中研究传统有机合成反应的机理是非常有意义的基础研究工作。本论文分析和总结了多氟取代醇的特点。如多氟取代醇特有的聚集态效应与电子效应，使其成为一个极强的氢键给体，能使阳离子寿命大幅度延长等特点。同时，基于多氟取代醇具有较低的沸点、良好的化学稳定性等特点，使其在用作有机合成反应溶剂后回收再利用上有操作简单的优势。因此，该论文的研究思路和目的是在多氟取代醇中研究芳烃的亲电取代反应机理，获取中间体生成的信息；同时建立等量亲电试剂参与的芳烃亲电取代反应体系。 论文工作选取1,1,1,3,3,3-六氟异丙醇为溶剂，重点研究芳烃硝化反应中间体生成的信息及其转化反应历程。首先研究了在强氧化性和强酸性的浓硝酸中(>90%)，1,1,1,3,3,3-六氟异丙醇具有结构稳定性，确认了以其作为芳烃硝化反应溶剂的可行性与安全性。同时，基于理论计算方法，从反应活化能、键离能的角度分析了2,2,2-三氟乙醇、1,1,1,3,3,3-六氟异丙醇等多氟取代醇和乙醇、异丙醇等烷基醇在浓硝酸存在下的不同化学稳定性的基本原因。然后，在1,1,1,3,3,3-六氟异丙醇中研究了芳烃与等当量硝酸的硝化反应，发现在室温下无论是富电子芳烃和苯，还是缺电子芳烃均具有良好的反应性，使用等当量的浓硝酸(>90%)时都可以高产率生成芳烃的硝化产物，建立了高效的芳烃硝化反应体系。 更重要的是，在1,1,1,3,3,3-六氟异丙醇溶剂中，发现在室温下用紫外可见光吸收光谱能直接观察到硝化反应体系中硝鎓离子与芳烃分子所形成的π-复合物中间体，同时论文进一步对反应过程中可能生成的中间体包含σ-复合物、π-复合物等物种进行了含时密度泛函理论计算，确认了实验观测到的光谱与理论预测的光谱结果确认了实验观测到的紫外可见吸收光谱是来自于形成π-复合物，验证了1,1,1,3,3,3-六氟异丙醇能稳定硝化反应中形成的阳离子型π-复合物中间体。
Organofluoro compounds are physically and chemically different from the corresponding hydrocarbons. For example, the use of polyfluorinated alcohols (PFAs) as a solvent will affect the efficiency and rate of organic reactions, as well as the formation of intermediates such as cations, anions, and free radicals. It has been found that PFAs play a significant role to promote some types of organic reactions. Therefore, it is of great scientific significance to study the mechanism of traditional organic reaction in PFAs.The characteristics of PFAs are analyzed and summarized in this dissertation. For example, PFAs have the special aggregation effect and electronic effect, resulting in being a very strong hydrogen bond donor to prolong the stability of cation greatly. On the other hand, on the basis of the relatively low boiling point and high chemical stability, PFAs have the advantages to be simply recovered after used as an organic solvent in organic synthesis. Therefore, the purpose of this dissertation is to study the electrophilic substitution of aromatics in a PFA to obtain the information of intermediates for understanding the mechanism, and also to develop the efficient electrophilic substitution reaction system of aromatics with the use of the equivalent of electrophilic reagents. In this research work, 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) is chosen as the solvent to study the formation of intermediates in the nitration of arenes and the transformation process of the intermediates. Firstly, the structural stability of HFIP was examined in the concentrated HNO3, which is a strong oxidant and strong acid, to confirm the feasibility and safety of HFIP as a solvent for the nitration of arenes. On the basis of the theoretical calculation of the bond dissociation energy and activation energy of nitration of 2,2,2-trifluoroethanol, HFIP, and alkyl alcohols such as ethanol and isopropanol, it has been disclosed that the major reasons for the different chemical stability of the alcohols in the presence of concentrated nitric acid. Secondly, the nitration of arenes with the use of the equivalent of nitric acid in HFIP was studied. It was found that at room temperature, both electron-rich arenes, benzene and electron-deficient arenes show good reactivity, and the nitrated products could be obtained in high yields when the equivalent of the concentrated nitric acid (>90%) was used, so as to develop an efficient nitration system for arenes. More importantly, in HFIP, it was found that the π-complex intermediate of an arene with a nitronium ion can be directly observed by UV-Vis spectra. The UV-Vis spectra of the possible intermediates in the reaction process including the ?-complex and π-complex intermediates are then calculated by using TD-DFT, and the predicted spectra support the experimentally observed spectra, which are resulting from the formation of the π-complex intermediates of an arene with nitronium ion. These obtained results verify that the cationic intermediates in nitration process of arenes are greatly stabilized by HFIP.
