title: Gas-phase Smiles rearrangement reactions of deprotonated N-phenylbenzamides studied by electrospray ionization tandem mass spectrometry.
abstract: BACKGROUND
  Electrospray ionization tandem mass spectrometry (ESI-MS(n)) is an invaluable tool for the study of gas-phase reactions. When N-phenylbenzamide is analyzed in negative ion mode, the nucleophilic deprotonated site of nitrogen or oxygen, together with the adjacent electrophilic phenyl carbon in the same molecule, provides a useful opportunity to study the intramolecular nucleophilic reaction in the gas phase.
  
  
  METHODS
  All MS(n) experiments of deprotonated N-phenylbenzamides were conducted on an ion trap mass spectrometer using ESI in negative ion mode. The accurate masses of fragments were measured on an ESI quadrupole time-of-flight mass spectrometer in negative ion mode. Theoretical calculations were conducted at the B3LYP/6-31++G(d,p) level of density functional theory using the Gaussian 03 program.
  
  
  RESULTS
  When the polarity of the substituent on the aniline ring was changed, gas-phase Smiles rearrangement reactions could be initiated by different atoms in the anionic center. Upon collisional activation, loss of CO from deprotonated N-phenylbenzamides could be observed, which can be interpreted as a nitrogen anion triggering the Smiles rearrangement reaction through a three-membered ring transition state. As the aniline ring was substituted by a strong electron-withdrawing group (e.g., NO(2), COCH(3), or CF(3)) at the para position, a characteristic phenolate anion was obtained, which was derived from the Smiles rearrangement reaction initiated by the oxygen anion through a four-membered ring transition state.
  
  
  CONCLUSIONS
  In the fragmentation of deprotonated N-phenylbenzamides, the gas-phase Smiles rearrangement reaction initiated by either the nitrogen or the oxygen atom can proceed. The findings in this study have not only enriched knowledge on the gas-phase Smiles rearrangement reactions, but also provided valuable information for understanding the rearrangements of deprotonated aromatic amides in gas phase.
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Yikun
authors.initials: Y
authors.lastname: Li
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Yunfeng
authors.initials: Y
authors.lastname: Chai
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Lin
authors.initials: L
authors.lastname: Wang
authors.affiliation: Department of Chemistry, Zhejiang University, Hangzhou, 310027, China.
authors.forename: Yuanjiang
authors.initials: Y
authors.lastname: Pan
authors.affiliation: College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China.
authors.forename: Su
authors.initials: S
authors.lastname: Zeng
authors.affiliation: College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, 310058, China.
authors.forename: Cuirong
authors.initials: C
authors.lastname: Sun
mesh_terms: D001549:Benzamides / Q000032:analysis* / Q000737:chemistry*; D005740:Gases; D007477:Ions; D008968:Molecular Conformation; D011522:Protons; D021241:Spectrometry, Mass, Electrospray Ionization / Q000379:methods*; D053719:Tandem Mass Spectrometry / Q000379:methods*
chemical_list: D001549:Benzamides; D005740:Gases; D007477:Ions; D011522:Protons