Alnajjar Radwan A, Jasiński Radomir
Department of Chemistry, Faculty of Science, University of Benghazi, Benghazi, Libya.
Department of Chemistry, University of Cape Town, Rondebosch, 7701, South Africa.
J Mol Model. 2019 May 11;25(6):157. doi: 10.1007/s00894-019-4006-7.
The competition between [2 + 1] and [4 + 1] channels regarding reactions of conjugated nitroalkenes with dichlorocarbene was explored based on B3LYP/6-31G(d) calculations. It was found that, in the case of cycloadditions involving parent nitroethene and its 1-substituted analogs, the [2 + 1] scheme should be treated as possible only from the kinetic process point of view. On the other hand, in similar reactions involving 2-substituted nitroethenes, both channels considered may compete. Additionally, mechanistic aspects of all cycloadditions were analyzed. It was found that the considered [2 + 1]-cycloadditions proceed via a non-polar mechanism with a biradicaloidal transition state (TS), whereas [4 + 1]-cycloadditions proceed via a polar mechanism with a zwitterionic TS.
基于B3LYP/6-31G(d)计算，研究了共轭硝基烯烃与二氯卡宾反应中[2 + 1]和[4 + 1]通道之间的竞争。研究发现，在涉及母体硝基乙烯及其1-取代类似物的环加成反应中，仅从动力学过程的角度来看，[2 + 1]反应途径才被视为可能。另一方面，在涉及2-取代硝基乙烯的类似反应中，所考虑的两种反应通道可能会相互竞争。此外，还分析了所有环加成反应的机理。研究发现，所考虑的[2 + 1]环加成反应通过具有双自由基过渡态（TS）的非极性机理进行，而[4 + 1]环加成反应通过具有两性离子过渡态的极性机理进行。
