Two Kinds Of Gas-phase Name Reactions In Electrospray Ionization Mas Spectrometry

Electrospray ionization (ESI) mass spectrometry, which creates solvent-free for gas phase reactions, can play an important role in understanding the intrinsic character of the reaction. In this thesis, two kinds of gas-phase names reactions have been investigated by ESI-MS/MS in combination with theoretical calculations, including the following two parts:1. Gas phase retro-Michael reaction resulting from dissociative protonation: fragmentation of protonated warfarin in mass spectrometryA mass spectrometric study of protonated warfarin and its derivatives has been performed. Losses of a substituted benzylideneacetone and a4-hydroxycoumarin have been observed as a result of retro-Michael reaction. The added proton is initially localized between the two carbonyl oxygens through hydrogen bonding in the most thermodynamically favorable tautomer. Upon collisional activation, the added proton migrates to the C-3of4-hydroxycoumarin, which is called the dissociative protonation site, leading to the formation of the intermediate ion-neutral complex (INC). Within the INC, further proton transfer gives rise to a proton-bound complex. The cleavage of one hydrogen bond of the proton-bound complex produces the protonated4-hydroxycoumarin while the separation of the other hydrogen bond gives rise to the protonated benzylideneacetone. Theoretical calculations indicate that the1,5-proton transfer pathway is most thermodynamically favorable, and supports the existence of the ion-neutral complex. Both substituent effect and the kinetic method were utilized for explaining the relative abundances of protonated4-hydroxycoumarin and protonated benzylideneacetone derivatives. For monosubstituted warfarins, the electron-donating substituents favor the generation of protonated substituted benzylideneacetone, whereas the electron-withdrawing groups favor the formation of protonated4-hydroxycoumarin.2. Gas-phase Smiles rearrangement of sulfonylurea herbicides in electrospray ionization mass spectrometryIn the negative ion mode of electrospray ionization tandem mass spectrometry (ESI-MS/MS) of four sulfonylurea herbicides, Smiles rearrangements were observed in rimsulfuron and nicosulfuron. In the case of rimsulfuron, two competitive gas-phase Smiles rearrangements initiated by nitrogen anion and oxygen anion respectively were witnessed. The ion-neutral complex was proposed as the reactive intermediate in the course of this unimolecular dissociation reaction of the oxygen attack Smiles rearrangement route. The density functional theory (DFT) was carried out to elucidate the mechanism as well as to show the possible transition states and the intermediates.