Intramolecular Electrophilic Aromatic Substitution in Gas-phase Fragmentation of ProtonatedN-Benzylbenzaldimines

Abstract

In this study, the gas-phase fragmentations of protonated N-benzylbenzaldimines were investigated by electrospray ionization tandem mass spectrometry (ESI-MS(n)). Upon collisional activation, several characteristic fragment ions are produced and their fragmentation mechanisms are rationalized by electrophilic aromatic substitution accompanied by benzyl cation transfer. (1) For N-(p-methoxybenzylidene)-1-phenylmethanimine, concomitant with a loss of HCN, a product ion at m/z 121 was observed. It is proposed to be generated from electrophilic substitution at the ipso-position by transferring benzyl cation rather than cleavage of the C-N double bond. (2) For N-(m-methoxybenzylidene)-1-phenylmethanimine, a product ion at m/z 209 was obtained, corresponding to the elimination of NH(3) carrying two hydrogens from the two aromatic rings respectively. This process can be rationalized by two sequential electrophilic substitutions and cyclodeamination reaction based on the benzyl cation transfer. Deuterium-labeled experiments, density functional theory (DFT) calculation and substituent effect results also corroborate the proposed mechanism.

Competitive proton and hydride transfer reactions via ion‐neutral complexes: fragmentation of deprotonated benzyl N‐phenylcarbamates in mass spectrometry

“…Nevertheless, ion a was the most abundant product ion, and ion b was the least abundant. The preferable generation of ion a results from an irreversible activation energy of the C(O)―O bond cleavage and a faster direct dissociation channel than the hydrogen transfer routes …”

“…The preferable generation of ion a results from an irreversible activation energy of the C(O)-O bond cleavage and a faster direct dissociation channel than the hydrogen transfer routes. [39,46] Conclusions An interesting INC-mediated mechanism involving competitive proton and hydride transfer reactions has been proposed for the fragmentation behavior of deprotonated benzyl N-phenylcarbamates in an ion trap mass spectrometer. The cleavage of the C(O)-O bond formed an INC intermediate consisting of a benzyloxy anion and a neutral phenyl isocyanate.…”

Benzyl anion transfer in the fragmentation of N-(phenylsulfonyl)-benzeneacetamides: a gas-phase intramolecular SNAr reaction

“…Last but not least, CID spectra of deprotonated 2-phenyl-N-tosylacetamide (9), N-((2,6-dichlorophenyl)sulfonyl)-2-phenylacetamide (10) and N-(mesitylsulfonyl)-2-phenylacetamide (11) were studied (Fig. Last but not least, CID spectra of deprotonated 2-phenyl-N-tosylacetamide (9), N-((2,6-dichlorophenyl)sulfonyl)-2-phenylacetamide (10) and N-(mesitylsulfonyl)-2-phenylacetamide (11) were studied (Fig.…”

Two competitive INC‐mediated reactions in the gas‐phase fragmentation of protonated indolyl benzo[b]carbazoles

“…

Mass spectrometry (MS) is commonly used nowadays in the structural analysis of a large variety of compounds, [1][2][3][4][5][6] including drugs, [5,6] metabolites, [3] particles, [1] intermediates, [4] and forensic evidence.[2] However, MS n -based structural elucidation has been challenging due to the widespread rearrangement reactions induced by ion-neutral complexes (INCs), [7][8][9][10] such as proton transfer, [8] electron transfer, [7,8] hydride transfer, [8] electrophilic aromatic substitution, [9] and nucleophilic aromatic substitution, [10] which have attracted the interest of many mass spectrometrists.Benzo [b]carbazoles are widely distributed in alkaloids and pharmaceuticals, which exhibit antitumor and antibiotic activities.[ [11] The direct infusion experiments were performed on a quadrupole time-of-flight (QTOF) mass spectrometer from (Bruker Daltonics, MA, USA) equipped with an ESI interface in positive ion mode. Typical parameters were set in the experiments, and theoretical calculations were performed by the density functional theory (DFT) method.

[12]

RESULTS AND DISCUSSION

A typical tandem mass spectrum for [1 + H] + at m/z 347 is depicted in Fig.

…”

“…[2] However, MS n -based structural elucidation has been challenging due to the widespread rearrangement reactions induced by ion-neutral complexes (INCs), [7][8][9][10] such as proton transfer, [8] electron transfer, [7,8] hydride transfer, [8] electrophilic aromatic substitution, [9] and nucleophilic aromatic substitution, [10] which have attracted the interest of many mass spectrometrists.…”