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

Focus: McLafferty Rearrangement

Abstract

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.

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Copyright information

© American Society for Mass Spectrometry 2004

Authors and Affiliations

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

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