Hydrogen Transfer And Fragmentation Reactions Mediated By Ion/Neutral Complexes In Electrospray Tandem Mass Spectrometry

Electrospray ionization mass spectrometry is not only an effective tool for structural characterization and compound identification in analytical investigation, but also an indispensable technique for the intrinsic reaction mechanism study in gas-phase ionic chemistry. Hydrogen transfers including proton transfer, hydrogen atom transfer, and hydride ion transfer are kinds of fundamental procedures occurring in gas-phase ionic reactions, which makes it an important thing to figure out the process in detail and get a comprehensive understanding of mass spectrometric behavior. In this thesis, two series of model compounds, that is benzyl sulfoxides and benzyl N-phenylcarbamates, have been investigated by ESI-MS/MS in combination with theoretical calculations. We have focused on their fragmentation behavior study, especially paid attention to the proton and hydride ion transfer process as well as their dissociation mechanisms. Two parts are included as follow:1. Hydrogen transfer and electrophilic substitution reactions via ion-neutral complexes:fragmentation of protonated benzyl sulfoxides in electrospray ionization tandem mass spectrometryUnder collision activation condition in ESI-MS, protonated benzyl sulfoxide gave rise to ion-neutral complexes containing benzyl cation. The benzyl cation can act as a Lewis acid and abstracted a hydride ion from the neutral counterpart to expel toluene. It can also play the role of electrophile either to attack the benzene to form σ-complexes or attack the oxygen atom to undergo sulfoxide-sulfenate rearrangement. Proton transfer occurred subsequently led to the neutral loss of benzene, sulfenic acid, formaldehyde and water forming several product ions. An intramolecular proton transfer catalysis process during the course of proton transfer from oxygen atom to sulfur atom was revealed. The INC-mediated mechanism was supported by high resolution MS, multistep MS deuterium-labeling experiments and theoretical calculations.2. Competitive proton and hydride transfer reactions via ion-neutral complexes: fragmentation of deprotonated benzyl N-phenylcarbamates in mass spectrometryAn interesting INC-mediated mechanism involving competitive proton and hydride transfer reactions has been proposed for the fragmentation behavior of deprotonated benzyl N-phenylcarbamates in an ion trap mass spectrometer. The cleavage of the C(O)-O bond formed an INC intermediate consisting of a benzyloxy anion and a neutral phenyl isocyanate. The benzyloxy anion could either abstract a proton or donate a hydride ion, whereas the neutral counterpart played the role of a proton donor or a hydride acceptor. The INC-mediated mechanism was supported by ortho-site-blocking, deuterium-labeling experiments and substituent effects along with theoretical calculations.