Premium
Collision‐induced dissociation processes of protonated benzoic acid and related compounds: competitive generation of protonated carbon dioxide or protonated benzene
Author(s) -
Xu Sihang,
Pavlov Julius,
Attygalle Athula B.
Publication year - 2017
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/jms.3920
Subject(s) - chemistry , protonation , benzene , dissociation (chemistry) , benzoic acid , carbon dioxide , photochemistry , organic chemistry , ion
Upon activation in the gas phase, protonated benzoic acid ( m/z 123) undergoes fragmentation by several mechanisms. In addition to the predictable water loss followed by a CO loss, the m/z 123 ion more intriguingly eliminates a molecule of benzene to generate protonated carbon dioxide ( H ‐ O + ═ C ≡ O , m/z 45), or a molecule of carbon dioxide to yield protonated benzene ( m/z 79). Experimental evidence shows that the incipient proton ambulates during the fragmentation processes. For the CO 2 or benzene loss, protonated benzoic acid transfers the charge‐imparting proton initially to the ortho position and then to the ipso position to generate a transient species which dissociates to form an ion‐neutral complex between benzene and protonated CO 2 . The formation of the m/z 45 ion is not a phenomenon unique to benzoic acid: spectra from protonated isophthalic acid, terephthalic acid, trans ‐cinnamic acid and some aliphatic acids also displayed a peak for m/z 45. However, the m/z 45 peak is structurally diagnostic only for certain benzene polycarboxylic acids because the spectra of compounds with two carboxyl groups on adjacent ring carbons do not produce a peak at m/z 45. For the m/z 79 ion to be formed, an intramolecular reaction should take place in which protonated CO 2 within the ion‐neutral complex acts as the attacking electrophile to transfer a proton to benzene. Copyright © 2017 John Wiley & Sons, Ltd.