Gas-phase reaction: alkyl cation transfer in the dissociation of protonated pyridyl carbamates in mass spectrometry

In the mass spectrometry of pyridyl carbamates, alkyl cation transfer is one of the major fragmentation reactions of the protonated molecules. Literature results and theoretical calculations indicate that the pyridine nitrogen is the most favorable site for protonation in these structures. Substituent and comparison experiments run to elucidate the fragmentation patterns reveal that the proton is localized at the pyridine nitrogen and the reaction center is charge-remote when the alkyl cation transfer occurs. The mechanism involving configuration inversion via an ion-neutral complex is favorable in energy for the alkyl cation transfer in these structures.