Interconversion of gas-phase arenium ions and .pi.-complexes
Interconversion of gas-phase arenium ions and .pi.-complexes
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气相芳烃离子和π-络合物的相互转化
DOI：
10.1021/ja00192a011
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发表时间：
1989
影响因子：
15
通讯作者：
M. Gross
中科院分区：
文献类型：
--
作者：
R. Holman;M. Gross
已知芳烃离子或络合物是作为亲电芳香取代（EAS）的中间体产生的，但络合物的存在不太确定。本文提供了芳烃气相质子化过程中 - 和 x-配合物共存的证据。在串联质谱仪的高压化学电离源中完成质子化，得到乙基苯鎓离子、异构的丙基苯鎓离子和丁基苯鎓离子以及五种异构的戊基苯鎓离子。已确定质子化可产生与稳定碳正离子烷基化（即通过 EAS）相同的离子。 x-络合物的存在与仲丁基苯鎓离子和仲丁基苯鎓离子的烷基部分在分解之前异构化的观察结果一致。如果异构化接近热中性，则可以直接检测到异构化。其他更多放热的异构化(例如，10烷基-*2烷基-*3烷基)仅被推断，因为释放的能量导致x-络合物分解成苯和碳正离子。通过使用碰撞激活解离 (CAD) 和串联质谱 (MS/MS) 获得异构化的证据。
Arenium ions or-complexes are known to be produced as intermediates in electrophilic aromatic substitution (EAS), but the existence of-complexes is less certain. Evidence is presented in this paper for the coexistence of- and x-complexes in the protonationof arenes in the gas phase. Protonation was accomplished in a high-pressure chemical ionization source of a tandem mass spectrometer to give the ethylbenzenium ion, the isomeric propyl-and butylbenzenium ions and five isomeric pentylbenzenium ions. It was established that identical ions are produced by protonation as are by alkylationwith stable carbenium ions (ie, by EAS). Theexistence of the x-complex is consistent with the observation that the alkyl moieties of secondary butyl-and pentylbenzenium ions isomerize prior to decomposition. The isomerization is directly detectable if it is nearly thermoneutral. Other more exothermic isomerizations (eg, Io alkyl—* 2 alkyl—* 3 alkyl) are only inferred because the energy released causes the x-complex to decompose to benzene and a carbenium ion. The evidence for isomerization was obtained by using collisionally activated dissociation (CAD) and tandem mass spectrometry (MS/MS).