Structure and fragmentation of C5H11O+ ions formed by chemical ionization

The proton transfer chemical ionization mass spectra of eleven C5H10O isomers have been obtained using H3+, N2H+, HCO+, and D3+ as reagent ions. The chemical ionization mass spectra in combination with isotopic labelling and metastable ion studies have made it possible to elucidate the major fragmentation reaction channels of the C5H11O+ ions formed and their dependence on precursor structure. From collision induced dissociation studies nine stable distinct C5H11O+ ion structures have been identified; protonated 3-methylbutanone and protonated 2,2-dimethylpropanal readily interconvert by a pinacolic – retro-pinacolic rearrangement.