Zabalov Maxim V, Karlov Sergey S, Lemenovskii Dmitri A, Zaitseva Galina S
Chemistry Department, Moscow State University, B-234 Leninskie Gory, 119899 Moscow, Russia.
J Org Chem. 2005 Nov 11;70(23):9175-84. doi: 10.1021/jo051085v.
[Structure: see text]. A DFT calculation study of the addition reaction between molecular bromine and the number of symmetrical or unsymmetrical substituted alkynes 1 (R-CC-R'), where R = R' = H (1a), Me (1b), t-Bu (1c), or Ph (1d), or R = H and R' = Me (1e), t-Bu (1f), or Ph (1g), was performed. Two possible reactions were checked: (a) the reactions suitable for the gas-phase interactions, which start from a 1:1 Br2-alkyne pi-complex and do not enter into a 2:1 Br2-alkyne pi-complex; and (b) the processes passing through a 2:1 Br2-alkyne pi-complex, which look more realistic for the reactions in solutions. The structures of the starting reactants and the final products as well as the possible stable intermediates have been optimized. The transition states of the predicted process have been found. Both trans- and cis-dibromoalkenes (2 and 3) may ensue without the formation of ionic intermediates from a pi-complex of two bromine molecules with the alkyne (solution reactions). The geometry around the double bond forming in dibromoalkenes strongly depends on the nature of the substituents at the triple bond. The "cluster model" was also used for the prediction of solvent influence on the value of the activation barrier of the but-2-yne (1b) bromination reaction.
[结构：见正文]。对分子溴与多种对称或不对称取代炔烃1（R−C≡C−R'）之间的加成反应进行了密度泛函理论（DFT）计算研究，其中R = R' = H（1a）、Me（1b）、t - Bu（1c）或Ph（1d），或者R = H且R' = Me（1e）、t - Bu（1f）或Ph（1g）。研究了两种可能的反应：（a）适用于气相相互作用的反应，该反应从1:1的Br₂ - 炔烃π络合物开始，不会形成2:1的Br₂ - 炔烃π络合物；（b）经过2:1的Br₂ - 炔烃π络合物的过程，这对于溶液中的反应似乎更符合实际情况。对起始反应物、最终产物以及可能的稳定中间体的结构进行了优化。找到了预测过程的过渡态。在没有离子中间体形成的情况下，两个溴分子与炔烃的π络合物（溶液反应）可能生成反式和顺式二溴烯烃（2和3）。二溴烯烃中形成的双键周围的几何结构强烈取决于三键处取代基的性质。“簇模型”也用于预测溶剂对2 - 丁炔（1b）溴化反应活化能垒值的影响。
