The simplest b2+ ion: Determining its structure from its energetics by a direct comparison of the threshold collision-induced dissociation of protonated oxazolone and diketopiperazine

► The structure of the b2+ ions derived from protonated GGG and GAG are shown to be oxazolones by comparison of their energetics for decomposition with theoretical calculations. ► The energetics and fragmentations patterns of the b2+ ions differ appreciably from the isobaric protonated diketopiperazine species. ► Because the higher energy processes involve substantial kinetic energy release, it is shown that statistical analyses of these pathways does not provide useful thermodynamic information.