TY - JOUR
T1 - Experimental and Theoretical Studies on Gas-Phase Fragmentation Reactions of Protonated Methyl Benzoate
T2 - Concomitant Neutral Eliminations of Benzene, Carbon Dioxide, and Methanol
AU - Xia, Hanxue
AU - Zhang, Yong
AU - Attygalle, Athula B.
N1 - Publisher Copyright:
© 2018, American Society for Mass Spectrometry.
PY - 2018/8/1
Y1 - 2018/8/1
N2 - 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. [Figure not available: see fulltext.].
AB - 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. [Figure not available: see fulltext.].
KW - Fragmentation
KW - Helium-plasma ionization
KW - HepI
KW - Methyl benzoate
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U2 - 10.1007/s13361-018-1997-8
DO - 10.1007/s13361-018-1997-8
M3 - Article
C2 - 29881998
AN - SCOPUS:85050162146
SN - 1044-0305
VL - 29
SP - 1601
EP - 1610
JO - Journal of the American Society for Mass Spectrometry
JF - Journal of the American Society for Mass Spectrometry
IS - 8
ER -