Fragmentation pathways of deprotonated ortho‐hydroxybenzyl alcohol

Abstract

The ortho, meta, and para isomers of hydroxybenzyl alcohol can be unequivocally distinguished by the collision‐induced dissociation mass spectra of their anions. The presence of a prominent peak at m/z 121 for an elimination of a dihydrogen molecule renders the ortho‐isomer spectrum markedly different from those of its meta and para congeners. Investigations carried out with deuterium‐labeled isotopologues of the ortho isomer verified that the labile hydrogen atom on the hydroxyl group and one of the benzylic hydrogen atoms are specifically removed in the formation of the m/z 121 ion. The ortho‐isomer spectrum also showed a prominent peak at m/z 93. Experimental data indicated that the m/z 93 product ion originates either from a two‐step H2and CO elimination mechanism or from a direct loss of a HCHO molecule from the precursor anion. The intensity ratio of the m/z 93 and 94 peaks in the spectrum recorded from the m/z 124 ion generated from a sample of o‐hydroxybenzyl alcohol dissolved in D2O supported the notion that the direct HCHO loss is the more dominant pathway for the generation of the phenolate ion under low activation conditions. In contrast, the two‐step mechanism becomes the more dominant pathway under high collisional activation conditions. The spectrum also showed a weak peak at m/z 105 for a water loss. Based on computational data, the m/z 105 ion generated in this way appears to be a composite generated from a common ion‐neutral complex intermediate in which a hydroxyl anion is positioned equidistantly between one of the benzylic hydrogens and a nearby hydrogen atom of the benzene ring. Upon activation, the complex dissociates to form either a phenide or a quinone methide anion. The reaction forming a carbon dioxide adduct under ion‐mobility conditions was used to support the proposed water‐loss mechanism.

Does deprotonated benzoic acid lose carbon monoxide in collision‐induced dissociation?

“…As a result of the consumption of phenide anion in the ion‐molecule reaction, the relative intensity of the expected fragment ion m/z 77 of deprotonated benzoic acid is very low. The generation of unlabeled benzoate anion ( m/z 121) from 18 O‐labeled benzoate anion ( m/z 125) further proves previous results that CO 2 attachment to aromatic anions occurs either in the fragmentation of their precursor anions in tandem mass spectrometry 8,9,28 or in ion‐molecule reactions 29,30 …”

“…DFT calculations show that the formation of phenoxide anion through the loss of CO is unfavorable (Figure S1). In view of the well-documented O 2 adduct formation in the fragmentation processes of gaseous ions, herein, the unexpected to aromatic anions occurs either in the fragmentation of their precursor anions in tandem mass spectrometry 8,9,28 or in ion-molecule reactions. 29,30 More benzoic acids bearing different electron-donating or electron-withdrawing groups and several fatty acids were studied using a Q-orbitrap mass spectrometer.…”

A computational and experimental study of cis–trans isomeric pesticides based on collision‐induced dissociation of high‐resolution mass spectrometry

“…However, these types of mass spectrometry are expensive and highly specific, making them difficult to popularize in ordinary laboratories. At present, most studies focus on the establishment of separation and analysis methods for isomeric pesticides, as well as the analysis of mass spectrometry cleavage pathways for a certain class of compounds 28–31 . Quantum chemical methods combined with collision‐induced dissociation (CID) on the mechanism of mass spectrometry separation and identification, as well as the effect of the mass spectrometry cleavage mechanism on different types of isomers, still account for a minority of studies 13…”

“…At present, most studies focus on the establishment of separation and analysis methods for isomeric pesticides, as well as the analysis of mass spectrometry cleavage pathways for a certain class of compounds. [28][29][30][31] Quantum chemical methods combined with collision-induced dissociation (CID) on the mechanism of mass spectrometry separation and identification, as well as the effect of the mass spectrometry cleavage mechanism on different types of isomers, still account for a minority of studies. 13 Radix Codonopsis, as a typical rhizome traditional Chinese medicine (TCM), has long been used to treat a variety of diseases containing bronchitis, cough, and allergic lung inflammation.…”