MO Study of Rearrangement of Ylides

1.在2-苯环N-亚甲基胺的[2，3]S型重排反应中，得到桥联化合物和螺环化合物。产物比取决于环状N-亚甲基铵的环大小。用AM1计算的起始叶立德构象很难预测产物。2.在N-取代-N，N-二甲基铵N-亚苄基的Stevens重排反应中，重排产物的产率受氮原子上取代基的影响。AM1或PM3计算的R-N^+键的解离能与产率之间的关系尚不清楚。3.用AM1或PM3模拟了N-亚甲基铵的Sommelet-Hauser重排和烯丙基重排反应机理。两种半经验方法显示了不同的势能面。AM1方法表明，烯丙基重排具有协同机制，Sommelet-Hauser重排具有分步机制。实验数据表明，S-亚甲基在S型重排反应中的化学行为与N-亚甲基不同。用B3LYP/6-31G和**&gt；水平对叶立德进行了从头算分子轨道研究。

1.Bridged compounds and spiro compounds were obtained in the [2,3] sigmatropic rearrangement of 2-benzocycloammonium N-methylides. The product ratio depended on the ring size of the cyclic ammonium N-methylide. It was difficult that the calculated conformations of the starting ylides by AM1 predict the products. Prediction of the product selectivity required analysis of the transition states of the rearrangement.2.In the Stevens rearrangement of N-substituted -N,N-dimethylammonium N-benzylides, the yield of the rearrangement products was influenced by the substituent on the nitrogen atom. The relationship between the yield and the calculated dissociation energies of R-N^+ bond by AM1 or PM3 was not recognized.3.Mechanisms of the Sommelet-Hauser rearrangement and the Allyl rearrangement of ammonium N-methylides were simulated by AM1 or PM3. The two semi-empirical methods showed different potential energy surfaces. The AM1 method has suggested that the Allyl rearrangement has a concerted mechanism, on the other hand, the Sommelet-Hauser rearrangement has a stepwise mechanism. Expreimental data showed that the chemical behavior of S-methylides in the sigmatropic rearrangements is different from that of the N-methylides. Abinitio MO study of the ylides by B3LYP/6-31G^<**> level are progressing.