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Thermally induced intramolecular oxygen migration of N ‐oxides in atmospheric pressure chemical ionization mass spectrometry
Author(s) -
Wang Xin,
Li Min,
Rustum Abu M.
Publication year - 2010
Publication title -
rapid communications in mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.528
H-Index - 136
eISSN - 1097-0231
pISSN - 0951-4198
DOI - 10.1002/rcm.4706
Subject(s) - chemistry , atmospheric pressure chemical ionization , mass spectrometry , chemical ionization , intramolecular force , photochemistry , amine oxide , mass spectrum , amine gas treating , ionization , ion , organic chemistry , chromatography , alkyl
N ‐Oxides are known to undergo three main thermal degradation reactions, namely deoxygenation, Cope elimination (for N ‐oxides containing a β‐hydrogen) and Meisenheimer rearrangement, in atmospheric pressure chemical ionization mass spectrometry (APCI‐MS). The ions corresponding to these thermal degradants observed in the ensuing APCI mass spectra have been used to identify N ‐oxides as well as to determine the N ‐oxidation site when the analyte contains multiple tertiary amine groups. In this paper, we report a thermally induced oxygen migration from one N ‐oxide amine to another tert ‐amine group present in the same molecule through a six‐membered ring transition state during APCI‐MS analysis. The observed intramolecular oxygen migration resulted in the formation of a new isomeric N ‐oxide, rendering the results of the APCI‐MS analysis more difficult to interpret and potentially misleading. In addition, we observed novel degradation behavior that happened after the Meisenheimer rearrangement of the newly formed N ‐oxide: a homolytic cleavage of the NO bond instead of elimination of an aldehyde or a ketone that usually follows the rearrangement. Understanding of these unusual degradation pathways, which have not been reported previously, should facilitate structural elucidation of N ‐oxides using APCI‐MS analysis. Copyright © 2010 John Wiley & Sons, Ltd.