Gas-Phase Chemistry of Benzyl Cations in Dissociation of N-Benzylammonium and N-Benzyliminium Ions Studied by Mass Spectrometry
Gas-Phase Chemistry of Benzyl Cations in Dissociation of N-Benzylammonium and N-Benzyliminium Ions Studied by Mass Spectrometry
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DOI：
10.1007/s13361-012-0344-8
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发表时间：
2012-05-01
影响因子：
3.2
通讯作者：
Pan, Yuanjiang
中科院分区：
文献类型：
--
作者：
Chai, Yunfeng;Wang, Lin;Pan, Yuanjiang
本研究采用电喷雾质谱法研究了n -苄基铵和n -苄基铵离子的破碎反应。一般来说，n -苄基化阳离子的解离很容易产生苄基阳离子。观察到由苄基阳离子和中性碎片组成的离子/中性络合物中间体的形成。配合物内反应包括亲电芳取代、氢化物转移、电子转移、质子转移和亲核芳取代。这五类反应几乎涵盖了化学反应中苄基阳离子的所有潜在反应活性。苄基阳离子在反应中被认为是路易斯酸和亲电试剂，但本研究表明，一些合适的环取代苄基阳离子的气相反应活性要丰富得多。发现4-甲基苄基阳离子作为Bronsted酸反应，发现带有强吸电子基团的苄基阳离子作为电子受体反应，对卤素取代的苄基阳离子可以作为底物在苯基环上发生亲核攻击。苄基阳离子的反应也与中性对应物有关。例如，在电子转移反应中，中性对应物应具有低电离能；在亲核芳香取代反应中，中性对应物应是哌嗪或类似物。本研究提供了苯离子与中性含n物质在气相中反应的全景图。
In this study, the fragmentation reactions of various N-benzylammonium and N-benzyliminium ions were investigated by electrospray ionization mass spectrometry. In general, the dissociation of N-benzylated cations generates benzyl cations easily. Formation of ion/neutral complex intermediates consisting of the benzyl cations and the neutral fragments was observed. The intra-complex reactions included electrophilic aromatic substitution, hydride transfer, electron transfer, proton transfer, and nucleophilic aromatic substitution. These five types of reactions almost covered all the potential reactivities of benzyl cations in chemical reactions. Benzyl cations are well-known as Lewis acid and electrophile in reactions, but the present study showed that the gas-phase reactivities of some suitably ring-substituted benzyl cations were far richer. The 4-methylbenzyl cation was found to react as a Bronsted acid, benzyl cations bearing a strong electron-withdrawing group were found to react as electron acceptors, and para-halogen-substituted benzyl cations could react as substrates for nucleophilic attack at the phenyl ring. The reactions of benzyl cations were also related to the neutral counterparts. For example, in electron transfer reaction, the neutral counterpart should have low ionization energy and in nucleophilic aromatic substitution reaction, the neutral counterpart should be piperazine or analogues. This study provided a panoramic view of the reactions of benzyl cations with neutral N-containing species in the gas phase.