TY - JOUR
T1 - Competitive homolytic and heterolytic decomposition pathways of gas-phase negative ions generated from aminobenzoate esters
AU - Xia, Hanxue
AU - Zhang, Yong
AU - Pavlov, Julius
AU - Jariwala, Freneil B.
AU - Attygalle, Athula B.
N1 - Publisher Copyright:
Copyright © 2016 John Wiley & Sons, Ltd.
PY - 2016/3/1
Y1 - 2016/3/1
N2 - An alkyl-radical loss and an alkene loss are two competitive fragmentation pathways that deprotonated aminobenzoate esters undergo upon activation under mass spectrometric conditions. For the meta and para isomers, the alkyl-radical loss by a homolytic cleavage of the alkyl-oxygen bond of the ester moiety is the predominant fragmentation pathway, while the contribution from the alkene elimination by a heterolytic pathway is less significant. In contrast, owing to a pronounced charge-mediated ortho effect, the alkene loss becomes the predominant pathway for the ortho isomers of ethyl and higher esters. Results from isotope-labeled compounds confirmed that the alkene loss proceeds by a specific γ-hydrogen transfer mechanism that resembles the McLafferty rearrangement for radical cations. Even for the para compounds, if the alkoxide moiety bears structural motifs required for the elimination of a more stable alkene molecule, the heterolytic pathway becomes the predominant pathway. For example, in the spectrum of deprotonated 2-phenylethyl 4-aminobenzoate, m/z 136 peak is the base peak because the alkene eliminated is styrene. Owing to the fact that all deprotonated aminobenzoate esters, irrespective of the size of the alkoxy group, upon activation fragment to form an m/z 135 ion, aminobenzoate esters in mixtures can be quantified by precursor ion discovery mass spectrometric experiments.
AB - An alkyl-radical loss and an alkene loss are two competitive fragmentation pathways that deprotonated aminobenzoate esters undergo upon activation under mass spectrometric conditions. For the meta and para isomers, the alkyl-radical loss by a homolytic cleavage of the alkyl-oxygen bond of the ester moiety is the predominant fragmentation pathway, while the contribution from the alkene elimination by a heterolytic pathway is less significant. In contrast, owing to a pronounced charge-mediated ortho effect, the alkene loss becomes the predominant pathway for the ortho isomers of ethyl and higher esters. Results from isotope-labeled compounds confirmed that the alkene loss proceeds by a specific γ-hydrogen transfer mechanism that resembles the McLafferty rearrangement for radical cations. Even for the para compounds, if the alkoxide moiety bears structural motifs required for the elimination of a more stable alkene molecule, the heterolytic pathway becomes the predominant pathway. For example, in the spectrum of deprotonated 2-phenylethyl 4-aminobenzoate, m/z 136 peak is the base peak because the alkene eliminated is styrene. Owing to the fact that all deprotonated aminobenzoate esters, irrespective of the size of the alkoxy group, upon activation fragment to form an m/z 135 ion, aminobenzoate esters in mixtures can be quantified by precursor ion discovery mass spectrometric experiments.
KW - McLafferty rearrangement
KW - aminobenzoate esters
KW - even-electron negative ions
KW - even-electron rule
KW - procaine, benzocaine, collision-induced dissociation
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U2 - 10.1002/jms.3740
DO - 10.1002/jms.3740
M3 - Article
C2 - 26956391
AN - SCOPUS:84960125392
SN - 1076-5174
VL - 51
SP - 245
EP - 253
JO - Journal of Mass Spectrometry
JF - Journal of Mass Spectrometry
IS - 3
ER -