Collisionally activated dissociation of N-acylpyridinium cations

Abstract

Relative fragmentation energies of a variety of N-acylpyridinium cations have been measured in the gas phase by electrospray ionization (ESI) Fourier transform ion cyclotron resonance mass spectrometry (FTICRMS). N-Aroyl- and N-heteroaroyl-pyridinium cations dissociated to give free ArCO⁺ ions with activation energies which are strongly decreased/increased by stabilizing/destabilizing electron-donor/acceptor substituents in the aroyl group. N-Alkylcarbonyl- and N-phenoxycarbonyl-pyridinium cations fragment via ion molecule complexes which dissociate to pyridinium cation and ketene or CO₂ + aryne. N-Alkoxycarbonylpyridinium cations form pyridinium cations via detectable N-carboxypyridinium cations. The propensity of those cations to undergo S_N1 or S_N2 reactions is discussed.