title: An experimental and computational investigation on the fragmentation behavior of enaminones in electrospray ionization mass spectrometry.
abstract: The dissociation pathways of protonated enaminones with different substituents were investigated by electrospray ionization tandem mass spectrometry (ESI-MS/MS) in positive ion mode. In mass spectrometry of the enaminones, ArCOCHCHN(CH(3) )(2) , the proton transfers from the thermodynamically favored site at the carbonyl oxygen to the dissociative protonation site at ipso-position of the phenyl ring or the double bond carbon atom adjacent to the carbonyl leading to the loss of a benzene or elimination of C(4) H(9) N, respectively. And the hydrogendeuterium (H/D) exchange between the added proton and the proton of the phenyl ring via a 1,4-H shift followed by hydrogen ring-walk was witnessed by the D-labeling experiments. The elemental compositions of all the ions were confirmed by ultrahigh resolution Fourier transform ion cyclotron resonance tandem mass spectrometry (FTICR-MS/MS). The enaminones studied here were para-monosubstituted on the phenyl ring and the electron-donating groups were in favor of losing the benzene, whereas the electron-attracting groups strongly favored the competing proton transfer reaction leading to the loss of C(4) H(9) N to form a benzoyl cation, Ar-CO(+) . The abundance ratios of the two competitive product ions were relatively well-correlated with the σ(p) (+) substituent constants. The mechanisms of these reactions were further investigated by density functional theory (DFT) calculations.
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou 310027, China.
authors.forename: Cheng
authors.initials: C
authors.lastname: Guo
authors.forename: Jieping
authors.initials: J
authors.lastname: Wan
authors.forename: Nan
authors.initials: N
authors.lastname: Hu
authors.forename: Kezhi
authors.initials: K
authors.lastname: Jiang
authors.forename: Yuanjiang
authors.initials: Y
authors.lastname: Pan
mesh_terms: D000475:Alkenes / Q000737:chemistry; D000588:Amines / Q000737:chemistry*; D001593:Benzyl Compounds / Q000737:chemistry*; D041961:Deuterium Exchange Measurement; D005583:Fourier Analysis; D006571:Heterocyclic Compounds / Q000737:chemistry*; D007659:Ketones / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D000475:Alkenes; D000588:Amines; D001593:Benzyl Compounds; D006571:Heterocyclic Compounds; D007659:Ketones; D011522:Protons