Metastable ion and induced stable ion fragmentation of isomeric 5‐methyl‐3‐tolyl‐1,2,4‐oxadiazoles

Abstract

AbstractThe electron ionization fragmentation patterns of 5‐methyl‐3‐(o‐, m‐ and p‐tolyl)‐1,2,4‐oxadiazoles (1a—c) have been examined by metastable ion and high resolution mass spectrometry. The o‐tolyl isomer loses CO and C2H2O from the metastable molecular ion whereas the m‐ and p‐tolyl isomers lose only CH3CN thus indicating a strong ortho effect in directing the fragmentation in 1a. Slight differences between o‐, m‐ and p‐tolyl isomers in the collisional activation fragmentation of stable [C7H6N]+ ions suggest that structural differences exist even after a series of extensive rearrangements of the molecular ions. Metastable ion kinetic energy (MIKE) and collisional activation (CA) spectra were very helpful in providing valuable information about many fragments.