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

Abstract

In this study, the fragmentation reactions of various N-benzylammonium and N-benzyliminium ions were investigated by electrospray ionization mass spectrometry. In general, the dissociation of N-benzylated cations generates benzyl cations easily. Formation of ion/neutral complex intermediates consisting of the benzyl cations and the neutral fragments was observed. The intra-complex reactions included electrophilic aromatic substitution, hydride transfer, electron transfer, proton transfer, and nucleophilic aromatic substitution. These five types of reactions almost covered all the potential reactivities of benzyl cations in chemical reactions. Benzyl cations are well-known as Lewis acid and electrophile in reactions, but the present study showed that the gas-phase reactivities of some suitably ring-substituted benzyl cations were far richer. The 4-methylbenzyl cation was found to react as a Brønsted acid, benzyl cations bearing a strong electron-withdrawing group were found to react as electron acceptors, and parahalogen-substituted benzyl cations could react as substrates for nucleophilic attack at the phenyl ring. The reactions of benzyl cations were also related to the neutral counterparts. For example, in electron transfer reaction, the neutral counterpart should have low ionization energy and in nucleophilic aromatic substitution reaction, the neutral counterpart should be piperazine or analogues. This study provided a panoramic view of the reactions of benzyl cations with neutral N-containing species in the gas phase.

Intramolecular Halogen Transfer via Halonium Ion Intermediates in the Gas Phase

“…The fragmentation reactions of organic compounds in multi-stage mass spectrometry are directly related to their structures, but the interpretation of mass spectra is not always straightforward because of many rearrangements that take place during fragmentation. In recent years, considerable research in ESI-MS has focused on studying the skeletal rearrangements of organic compounds, including alkyl transfer [24,25], benzyl cation transfer [26][27][28][29][30], benzoyl cation transfer [31], phosphate group migration [32], intramolecular electrophilic substitution [33,34], tosyl cation transfer [35], and ion/neutral complexmediated fragmentations [36][37][38][39].…”

Síntesis de nuevos líquidos iónicos y evaluación de su rendimiento de lixiviación en la recuperación de cobre y zinc de escorias industriales de latón

“…The universal method of preparing ionic liquids is the alkylation of a suitable heteroatom containing organic molecules to form the cation (Chai et al, 2012). After the alkylation, the anion is changed to the one desired.…”

Decarboxylative Coupling Reaction in ESI(−)-MS/MS of 4-Nitrobenzyl 4-Hydroxybenzoates: Triplet Ion–Neutral Complex-Mediated 4-Nitrobenzyl Transfer

“…The sum of the free energy of the separated 2-methoxy-4-carboxylate-phenoxyl and nitrobenzyl radicals is higher than that of 1-INC-t by 24.7 kJ/mol; this indicates that 1-INC-t is relatively stable. INC is an important intermediate in gasphase chemistry, and various chemical reactions can occur between the two species or in the ionic fragment alone prior to its final separation [6,8,17,[19][20][21][22][23][24]. In addition to direct separation to Figure 5S).…”

“…However, the gasphase C-C coupling reactions such as methyl and benzyl transfers that occur in tandem mass spectrometry (MS/MS) often cause problems in MS-based structural elucidations, and have therefore attracted much attention [4][5][6][7]. Benzyl cations are relatively stable in the gas phase and are easily formed during MS by fragmentation of benzylated species [8,9]. Migration of a benzyl cation to a methylene group (especially of an aromatic ring) leads to C-C/C-N coupling reactions [5,9].…”