Energy‐dependent dissociation of benzylpyridinium ions in an ion‐trap mass spectrometer

Abstract

Benzylpyridinium ions, generated via electrospray ionization of dilute solutions of their salts in acetonitrile/water, are probed by collisional activation in an ion-trap mass spectrometer. From the breakdown diagrams obtained, phenomenological appearance energies of the fragment ions are derived. Comparison of the appearance energies with calculated reaction endothermicities shows a reasonably good correlation for this particular class of compounds. In addition, the data indirectly indicate that at threshold the dissociation of almost all of the benzylpyridinium ions under study leads to the corresponding benzylium ions, rather than the tropylium isomers. Substituent effects on the fragmentation for a series of benzylpyridinium ions demonstrate that neither mass effects nor differences in density of states seriously affect the energetics derived from the ion-trap experiments.

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

“…It is noteworthy that the ion at m/z 91 here should be benzyl cation. Previous theoretical studies suggested that conversion of the benzyl cation to the tropylium ion must surmount a significant energy barrier (65.0 kcal mol −1 [30], 67.8 kcal mol −1 [31]), so this process was usually not considered to occur in ESI mass spectrometry [32,33] though rare exceptions had been reported in the fragmentations of some benzylpyridinums [34][35][36]. For the occurrence of intra-complex reaction, INC-1 should have suitable amount of internal energy, which is enough for further reaction between the ion and the neutral species but not enough for direct separation.…”

Gas-Phase Chemistry of Benzyl Cations in Dissociation ofN-Benzylammonium andN-Benzyliminium Ions Studied by Mass Spectrometry

“…In electrospray ionization mass spectrometry (ESI-MS), fragmentation of benzylated cations prefers to generate benzyl cations [7,8,[20][21][22][23][24][25][26][27][28][29][30], though a few exceptions have been reported that tropylium ion can be co-produced in the fragmentation of benzylpyridinium ions [18,31,32]. Besides the formation of benzyl cations, other interesting ions resulting from hydride transfer [24,25] or electrophilic aromatic substitution reactions [20][21][22] via the nonconventional ion/neutral complex (INC) can also be generated in the dissociation of benzylated cations.…”

Surface Acoustic Wave Nebulization Produces Ions with Lower Internal Energy than Electrospray Ionization

“…The precursor ion dissociates into a fragment ion (benzylium ion A or tropylium ion B) and a neutral pyridine molecule [18,26,27]. In order to derive ion internal energies from the measurements of ion survival yields, the dissociation energies for each BzPy ion are required.…”

“…Fragmentation by bond cleavage between the benzyl and pyridinium moieties occurs for all substituted BzPy ions. Thus, a typical mass spectrum for a substituted BzPy ion contains two peaks, one for the precursor ion and one for the main fragment ion due to the loss of pyridine [18]. The corresponding ion dissociation energetics of BzPy ions have been mainly obtained by electronic structure calculations of varying quality and used as a reference to estimate the internal energy of conventional ionization methods, such as MALDI [19,20], ESI [16,21], desorption electrospray ionization (DESI) [22], direct analysis in real time (DART) [23], and silicon nanoparticle-assisted laser desorption/ionization (SPALDI) [24].…”