Relative Reactivities of Three Isomeric Aromatic Biradicals with a 1,4‐Biradical Topology Are Controlled by Polar Effects
作者:Xin Ma、Chunfen Jin、Duanda Wang、John J. Nash、Hilkka I. Kenttämaa
DOI:10.1002/chem.201806106
日期:2019.5.2
5‐dehydroquinoline radical cation was formed in the gas phase from the 5‐iodo‐8‐nitroquinolinium cation upon ion‐trap collision‐activated dissociation. This reaction involves the cleavage of a nitro group to generate an intermediate monoradical, namely, the 8‐dehydro‐5‐iodoquinolinium cation, followed by rearrangement through abstraction of a hydrogen atom from the protonated nitrogen atom by the radical site.
出乎意料的是,在离子阱碰撞活化解离后,由5-碘-8-硝基喹啉鎓阳离子在气相中形成了5-脱氢喹啉自由基阳离子。该反应涉及硝基的裂解以生成中间体单自由基,即8-脱氢-5-碘喹啉鎓阳离子,然后通过自由基位点从质子化的氮原子中夺取氢原子进行重排。通过消除碘原子使重排的自由基阳离子解离,生成5-dehydroquinoline自由基阳离子。通过研究异构双自由基并进行量子化学计算来探索该机理。5-脱氢喹啉自由基阳离子对二甲基二硫,环己烷和烯丙基碘的气相反应性比5,8-二氢喹啉阳离子同分异构体更高,它比以前研究的同分异构的5,8-二氢杂喹啉阳离子更具反应性。所有三个异构体均具有1,4-双自由基的拓扑结构。这些双自由基的自由基位置的垂直电子亲和力,而不是它们之间相差甚远的单重态-三重态分裂,使反应顺序得以合理化。