Ion-Neutral Complexes as Intermediates in the Decompositions of C5H10O2.+ Isomers

Article abstract of DOI:10.1021/ja00259a012

Ionized pentanoic acid, 3-methylbutanoic acid, and the enol isomer of ionized isopropyl acetate are shown to pass in part through common intermediates before decomposing to CH3C^.HC(OH)2⁺ (7) and the "McLafferty + 1" ion CH3C(OH)2⁺ (10).The H transfer to form the methyl of CH3C(OH)2⁺ and the joining of two CH2 groups to form the C-C bond in the ethylene eliminated to produce CH3C^.HC(OH)2⁺ are both attributed to reactions of the ion-neutral complex .H2C(OH)2⁺>.The McLafferty + 1 ion is also formed, especially from ionized esters, by another pathway in which complexes may or may not be intermediates.The intermediacy of the ion-neutral complexes is supported by energetic considerations, isotope effects, and the decomposition patterns of labeled ions.The latter correlate with a preference for hydrogen transfer from the end carbons of the C3 partner in other reactions proposed to be complex-mediated.Unification of the McLafferty rearrangement, the McLafferty + 1 rearrangement, and the McLafferty rearrangement with charge reversal by a common initial γ-hydrogen rearrangement followed by dissociation or isomerization in ion-neutral complexes is proposed.Group migration by 1,2-shifts, possibly by dissociation to form a double bond in one partner in an ion-neutral complex followed by addition at the opposite end of the double bond, is shown to be a general reaction of ions in the gas phase.