Gas‐phase dissociation of 1,4‐naphthoquinone derivative anions by electrospray ionization tandem mass spectrometry

Abstract

Gas-phase dissociation pathways of deprotonated 1,4-naphthoquinone (NQ) derivatives have been investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS). The major decomposition routes have been elucidated on the basis of quantum chemical calculations at the B3LYP/6-31 + G(d,p) level. Deprotonation sites have been indicated by analysis of natural charges and gas-phase acidity. NQ anions underwent an interesting reaction under collision-induced dissociation conditions, which resulted in the radical elimination of the lateral chain, in contrast with the even-electron rule. Possible pathways have been suggested, and their mechanisms have been elucidated on the basis of Gibbs energy and enthalpy values for the anions previously described at each pathway.

Gas‐phase reactivity of protonated 2‐oxazoline derivatives: mass spectrometry and computational studies

“…Several methodologies have been employed to confirm the most stable protonation site in organic compounds, and there are some models that accurately describe the protonation sites in the gas phase . The combination between atomic charges, frontier orbitals, Fukui functions, and energetic parameters, such as proton affinities (PA) and gas‐phase basicity (GB), have been satisfactorily used by us to indicate the most probable site for proton attachment . However, the PA and GB parameters have demonstrated to be the most useful for the identification of protonation sites.…”

“…However, investigation of protonated oxazoline is important, so that the reactivity of this class of compounds in the gas phase can be better understood. Electrospray ionization mass spectrometry (ESI‐MS) is an important tool for the analysis of synthetic, semi‐synthetic, and natural products . MS/MS studies with an ESI source have been conducted for characterization and structural elucidation, because the fragmentation pathways can furnish valuable information about the reactivity of new compounds, and the established mechanisms can aid the elucidation of other classes of compounds .…”

N-Centered Odd-Electron Ions Formation from Collision-Induced Dissociation of Electrospray Ionization Generated Even-Electron Ions: Single Electron Transfer via Ion/Neutral Complex in the Fragmentation of ProtonatedN,N′-Dibenzylpiperazines and ProtonatedN-Benzylpiperazines

“…When these closed-shell ions are subjected to CID, they commonly dissociate to daughter closed-shell ions and neutral fragments based on 'even-electron rule' [1]. It is rare that an electrospray ionization generated even-electron (EE) ion directly dissociates to form an odd-electron (OE) ion, though exceptions are more common in electron ionization (EI) [1][2][3][4] than in ESI mass spectrometry [5][6][7][8][9][10][11][12]. It is significant and desirable to investigate the underlying mechanism of formation of OE ions from EE ions because such considerations are important for a better understanding of ESI mass spectrometry.…”

Electrospray ionization tandem mass spectrometry of labdane‐type acid diterpenes

“…To optimize the product ion spectra of the deprotonated labdane‐type acid diterpenes 1 to 4 , we first varied the collision energy (E lab ) values between 5 and 60 eV. The collision energy of choice should reduce the precursor ion ([M–H] − ) relative intensities in the product ion spectrum to 25% to 50% and generate a significant number of product ions with relative intensities higher than 10% without extensive fragmentation . In this study, the collision energy (E lab ) at 35 eV decreases the relative intensities of the precursor ions of compounds 1 to 3 to 50%.…”