Two competing ionization processes in ESI-MS analysis of N-(1,3-diphenylallyl)benzenamines: formation of the unusual [M−H]⁺ ion versus the regular [M+H]⁺ ion

Abstract

A series of N-(1,3-diphenylallyl)benzenamine derivatives (M) were investigated by electrospray ionization mass spectrometry in the positive-ion mode. Both the anomalous [M-H] and the regular [M+H] were observed in the ESI mass spectra. The occurrence of [M-H] has been supported by accurate mass spectrometry, liquid chromatography mass spectrometry, and tandem mass spectrometry analysis. Calculation results indicated that formation of [M-H] is attributed to the ion-molecule reaction of M with the protonated ESI solvent molecule (e.g. CHOH) via hydride abstraction from a tertiary C-H. The competing ionization processes leading to [M-H] or [M+H] were significantly affected by the concentration of formic acid in the electrospray ionization solvent and the proton affinity of the N atom.

Hydralazine derivative of aldehyde: A new type of [M − H]+ ion formed in electrospray ionization mass spectrometry

“…The free energies of the [Comp1 + H] + ion and [Comp1 − H] + ion were then compared in order to explore the possible formation pathway. According to previous literature, there were three possible pathways for the generation of the [Comp1 − H] + ion (Figure ), including (a) a direct loss of H − ; (b) a loss of H· and an electron; and (c) a loss of H 2 after protonation. The calculated relative free energies for these three pathways were 209.7, 214.5, and −202.8 kcal mol −1 , respectively.…”

“…For this type of compounds, chiral C‐3 alkyl‐substituted indoles, diarylmethylamine, cyclopenta[b] indoles, and bisindolylmethanes were designed for the formation of [M − H] + ion in gas phase. As for the last type, it was reported that the protonated ESI solvent molecule could induce a neutral loss in the ESI source to generate [M − H] + ion . These previous researches provided supplementary information for understanding the properties of these compounds in gas phase and electrospray ionization process.…”

Formation of the exceptional [M − H]+ cation in atmospheric pressure ionization mass spectrometry analysis of 2‐(diphenylsilyl) cyclopropanecarboxylate esters

“…37 The equilibrium geometries of the target species were optimized using the density functional theory method at the When the ESI solvent was acidified by the addition of 0.1% FA, the ion at m/z 357 rather than [1 + Na] + became the base peak ( Figure 1B). Normally, the addition of trace formic acid to the ESI solvent can significantly improve the signal of the [M + H] + ion in ESI-MS. [18][19][20][21] In…”

“…Atmospheric pressure ionization (API), electrospray ionization (ESI), and atmospheric pressure chemical ionization (APCI) are widely used ionization techniques for mass spectrometry (MS). [1][2][3][4][5] [6][7][8][9] However, an increasing number of studies have reported the synthesis of some exceptional ions, resulting from reactions between analytes and solvents, 10,11 electrochemical redox reactions of analytes, 9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27] or selfcyclocondensation. 28 The presence of these unusual ions seriously complicates the mass spectra and can impair quantitative detection.…”

“…This process has been reported in the ESI(+)-MS analysis of several nitrogen heterocyclic compounds, such as 1,4-dihydropyridines, 18 cyclopenta[b]indoles, 19 3-alkylsubstituted indoles, 20 and N- (1,3-diphenylallyl)benzenamines. 21 Compounds with a Si-H group in their structure have been widely used for the catalytic silanization of alkenes in organic synthesis, pharmaceutical chemistry, and functional materials. [29][30][31][32] These compounds are also important reducing agents in organic reactions.…”