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首页> 外文期刊>Journal of the American Society for Mass Spectrometry >Experimental and Theoretical Studies on Gas-Phase Fragmentation Reactions of Protonated Methyl Benzoate: Concomitant Neutral Eliminations of Benzene, Carbon Dioxide, and Methanol
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Experimental and Theoretical Studies on Gas-Phase Fragmentation Reactions of Protonated Methyl Benzoate: Concomitant Neutral Eliminations of Benzene, Carbon Dioxide, and Methanol

机译：质子化甲酸甲酯气相破碎反应的实验与理论研究：烯烃，二氧化碳和甲醇的伴随中性消除

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摘要

Protonated methyl benzoate, upon activation, fragments by three distinct pathways. The m/z 137 ion for the protonated species generated by helium-plasma ionization (HePI) was mass-selected and subjected to collisional activation. In one fragmentation pathway, the protonated molecule generated a product ion of m/z 59 by eliminating a molecule of benzene (Pathway I). The m/z 59 ion (generally recognized as the methoxycarbonyl cation) produced in this way, then formed a methyl carbenium ion in situ by decarboxylation, which in turn evoked an electrophilic aromatic addition reaction on the benzene ring by a termolecular process to generate the toluenium cation (Pathway II). Moreover, protonated methyl benzoate undergoes also a methanol loss (Pathway III). However, it is not a simple removal of a methanol molecule after a protonation on the methoxy group. The incipient proton migrates to the ring and randomizes to a certain degree before a subsequent transfer of one of the ring protons to the alkoxy group for the concomitant methanol elimination. The spectrum recorded from deuteronated methyl benzoate showed two peaks at m/z 105 and 106 for the benzoyl cation at a ratio of 2:1, confirming the charge-imparting proton is mobile. However, the proton transfer from the benzenium intermediate to the methoxy group for the methanol loss occurs before achieving a complete state of scrambling.
机译：在活化后苯甲酸酯质子化甲酸酯，碎片三种不同的途径。由氦 - 血浆电离（HEPI）产生的质子化物种的M / Z 137离子被质量选择并进行碰撞活化。在一个碎片途径中，通过消除苯（途径I）分子产生质子化分子的产物离子。以这种方式制备的M / Z 59离子（通常识别为甲氧基羰基阳离子），然后通过脱羧形成甲基碳离子原位，这反过来通过结局过程诱发在苯环上的亲电芳族加成反应以产生甲苯阳离子（途径II）。此外，质子化甲酸甲酯也经过甲醇损失（途径III）。然而，在甲氧基的质子化之后，它不是在甲氧基质的质子化之后简单地除去甲醇分子。初期的质子迁移到环并在随后将一个环形质子转移到烷氧基的一定程度上随机转移到烷氧基，以伴随甲醇消除。从氘化甲基苯甲酸甲酸酯记录的光谱在M / Z 105和106处显示出两个峰，用于苯甲酰基为2：1的比例，确认电荷赋予质子是移动的。然而，在实现完整的加扰状态之前，从苯并苯中间体中间体转移到甲醇损失的质子转移。

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