Gas‐phase Smiles rearrangement reactions of deprotonated N‐phenylbenzamides studied by electrospray ionization tandem mass spectrometry. (25th March 2015)

• Record Type: Journal Article
• Authors: Li, Yikun; Chai, Yunfeng; Wang, Lin; Pan, Yuanjiang; Zeng, Su; Sun, Cuirong
• Is Part Of: Rapid communications in mass spectrometry. Volume 29:Number 9(2015)
• Page Start: 864
• Page End: 870
• Publication Date: 2015-03-25
• Subjects: Mass spectrometry -- Periodicals; 543.65
• DOI: 10.1002/rcm.7172
• Languages: English
• ISSNs: 0951-4198

Abstract

Abstract : Rationale: 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., NO2, COCH3, or CF3 ) 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. Copyright © 2015 John Wiley & Sons, Ltd.