Center for Mass Spectrometry, Department of Chemistry, Chemical Biology, and Biomedical Engineering, Stevens Institute of Technology, Hoboken, NJ 07030, USA.
J Am Soc Mass Spectrom. 2011 Sep;22(9):1515-25. doi: 10.1007/s13361-011-0164-2. Epub 2011 Jun 3.
The diagnostic value of the "ortho effect" for unknown identification by mass spectrometry is well known. Here, we report the existence of a novel "meta effect," which adds to the repertoire of useful mass spectrometric fragmentation mechanisms. For example, the meta-specific elimination pathway described in this report enables unequivocal identification of meta isomers from ortho and para isomers of carboxyanilides. The reaction follows a specific path to eliminate a molecule of meta-benzyne, from the anion produced after the initial decarboxylation of the precursor. Consequently, in the CID spectra of carboxyanilides, a peak for the (R-CO-NH)(-) anion is observed only for the meta isomers. For example, the peaks observed at m/z 58, 86, 120, 128, and 170 from acetamido-, butamido-, benzamido, heptamido-, and decanamido-benzoates, respectively, were specific only to the spectra of meta isomers.
“邻位效应”在质谱法中对未知物的鉴定具有重要的诊断价值，这是众所周知的。在这里，我们报告了一种新的“间位效应”的存在，它增加了有用的质谱碎裂机制的范围。例如，本报告中描述的间位特异性消除途径可用于从羧酸酰胺的邻位和对位异构体中明确鉴定间位异构体。该反应遵循特定的路径，从前体初始脱羧后生成的阴离子中消除间苯乙炔分子。因此，在羧酸酰胺的 CID 谱中，仅观察到间位异构体的（R-CO-NH）（-）阴离子的峰。例如，从乙酰胺基、丁酰胺基、苯甲酰胺基、庚酰胺基和癸酰胺基苯甲酸酯中分别观察到 m/z 58、86、120、128 和 170 的峰仅出现在间位异构体的谱中。
