稳定的腈阳离子盐是多种重要有机反应的中间体。与它有关的反应引起了化学工作者的极大兴趣。其中涉及到的杂原子烯反应和Houben-Hoesch反应都在有机合成中具有广泛用途。从理论上来研究这些反应的反应机理，有助于理解反应发生的过程，为合成工作提供指导，有着重要的理论和实际意义。在本文中，我们使用B3LYP方法，PCM/UAHF(Alpha=1.40)溶剂化模型，讨论了腈阳离子与2-甲基噻吩在溶液条件下反应的反应机理。得到以下结论：1．选择C-甲基-N-甲基腈阳离子与2-甲基噻吩的反应作为模型反应，讨论了它在乙腈溶液中的反应机理。结果表明，它有两个可能的反应通道：Houben-Hoesch反应通道和烯反应通道。在这两个通道中，六氯锑酸根和乙腈溶剂都对质子迁移过程起了催化作用。在Houben-Hoesch反应中，六氯锑酸根催化质子迁移和直接1, 3-质子迁移都能得到顺式和反式亚胺盐。烯反应通道中包含了多个反应步骤，其中最后一步质子迁移经历了一个形式上的6-(3, 5) 烯环化过程，但是在的机理上，它的过程非常复杂。与实验预计有所不同的是，这个过程中有乙腈的参与。不同的PCM计算表明，PCM/UAHF在描述最后一步质子迁移过程时是最好的，而其它大多数模型都会带来多余的虚振动频率。2．在二氯甲烷（CH2Cl2）溶剂中计算了C-甲基-N-苯基腈阳离子与2-甲基噻吩的反应的反应机理。该反应只有Houben-Hoesch反应通道。它是在六氯锑酸根阴离子的催化下完成的。这个过程需要越过的最高能垒为15.94 Kcal/mol，在室温下很容易进行。计算结果还表明，在产物中，腈阳离子的C端取代基和N端取代基总是处于反式。这与实验结果相一致。3．在乙腈溶剂中计算C-苯基-N-异丙基腈阳离子与2-甲基噻吩反应的反应机理。该反应的机理与模型反应类似，存在烯反应通道和Houben-Hoesch反应通道。其中，烯反应通道能垒较低，在室温条件下很容易进行。而Houben-Hoesch反应却需要相对较高的能量，因为这个原因，在实验中没能观察到和分离出该反应产物。值得一提的是，在最后一步质子迁移中，溶剂乙腈起了至关重要的作用。

Stable nitrilium ions, as the intermediates of reactions, are of paramount importance in organic synthesis. Extensive attention has been paid to this field, especially on the reactions between alkenes, arenes and nitrilium ions, of which hetero-ene reaction and Houben-Hoesch reaction are versatile use in organic chemistry and have prosperous future in applied synthesis. For better understanding the reactions and directing the synthesis, it is necessary to theoretically investigate the mechanisms of those reactions. In this thesis, B3LYP method employing PCM/UAHF (Alpha=1.40) SCRF model has been used to investigate the mechanisms of the reactions between nitrilium ions and 2-methylthiophene to mimic real experimental condition. The main results and conclusions obtained are summarized as follows:1.For the model reaction of N-methylmethylnitrilium hexachloroantimonate with 2-methylthiophene, all of calculations have been performed in acetonitrile solvent. The obtained results indicate that there exist two probable reaction pathways: Houben-Hoesch reaction route and the ene reaction route. Extensive search on the potential energy surface indicated that both hexachloroantimonate anion and acetonitrile could take part in the reactions as the role of catalyst in the steps of proton transfer. In Houben-Hoesch reaction, both cis- and trans- iminium salts can be obtained either by the catalysis of the anion or by direct 1, 3-hydrogen transfer. The ene reaction route involves multiple steps, in which the last step of proton transfer process is a formal 6-(3, 5) ene cyclization, but the real reaction mechanism is quite complicated and different from what experiments suggested with the involving of solvent acetonitrile. Different PCM calculatons indicate that PCM/UAHF is the best one in characterizing the last proton transfer process, since most of other models have resulted in the redundant imaginary frequencies.2.For the reaction of N-phenylmethylnitrilium hexachloroantimonate with 2-methylthiophene in CH2Cl2 solvent, only Houben-Hoesch reaction that is promoted by the catalysis of hexachloroantimonate anion could be located and characterized, with the highest energy barrier being 15.94kcal/mol, indicateing that it is easy accessible in real experimental temperature. It is interesting that the original two substituents in N-phenylmethylnitrilium are always on the trans position in the final product, which is in good agreement with the real experimental result.3.For the reaction between N-Isopropylbenzonitrilium hexachloroantimonate and 2-methylthiophene in acetonitrile, the characterized reaction mechanism is the same as model reaction. The energy barrier of the ene reaction route is very low, indicating that the ene reaction can take place in ambient temperature. However, Houben-Hoesch reaction needs relatively high energy to be proceeded. This is the reason why no Houben-Hoesch product could be observed and separated. Furthermore, solvent acetonitrile plays an important role in the last step of proton transfer.