Gas phase ion chemistry of the heterocyclic isomers 3-methyl-1,2-benzisoxazole and 2-methyl-1,3-benzoxazole

  • Gianluca GiorgiEmail author
  • Laura Salvini
  • Fabio Ponticelli
Focus: McLafferty Rearrangement


Different mass spectrometric methods, stable isotope labeling, and theoretical calculations have allowed us to structurally characterize and differentiate the isomeric ion structures produced by the two heteroaromatic isomers 3-methyl-1,2-benzisoxazole and 2-methyl-1,3-benzoxazole. The low-energy collision induced dissociation spectra of their molecular ions show large differences. Although both of them produce abundant loss of CO, that involves a carbon atom of the benzene ring, the 2-methyl-1,3-benzoxazole also shows abundant [M-CHO]+ ions at m/z 104, the intensity of which is quite low in the case of its isomer 3-methyl-1,2-benzisoxazole. In addition, MS/MS measurements of fragment ions show characteristic differences that allow distinction among the isomers depending on the original arrangement of the atoms in the five-membered ring. Theoretical ab initio calculations have allowed to determine chemico-physical properties of different ions and to propose a rationalization of the decomposition pathways followed by the two benz(is)oxazole isomers.


Radical Cation Electron Ionization Mass Spectrometry Electron Ionization Mass Spectrum Cinnolines Induce Collision Dissocia 
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Copyright information

© American Society for Mass Spectrometry 2004

Authors and Affiliations

  • Gianluca Giorgi
    • 1
    Email author
  • Laura Salvini
    • 1
  • Fabio Ponticelli
    • 1
  1. 1.Dipartimento di Chimica and Centro di Analisi e Determinazioni StrutturaliUniversità di SienaSienaItaly

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