Unexpected Course Of Olefin Loss From Some Alkylcyclopentanone Ions - Gaseous Ion Structure By Ion-Cyclotron Resonance Spectrometry, Mass-Analyzed Ion Kinetic-Energy Spectrometry And Collision-Induced Dissociation

Ion cyclotron resonance results show that the ions formed by single and by double McLafferty rearrangement in 2-ethyl-5-propylcyclopentanone have neither keto nor enol structures. Collision-induced dissociations confirm that these ions are structurally distinct from the keto ions formed directly by electron impact upon the corresponding neutral molecules. It is suggested that the major reaction path for olefin loss from 2-ethyl-5-propylcyclopentanone and from 2-ethylcyclopentanone involves ring opening followed by hydrogen transfer to carbon in the alkene elimination step. Only in metastable ions is there evidence for the occurrence of the normal McLafferty rearrangement. The techniques mentioned in the title, together with conventional low and high resolution mass spectrometry, have been used to characterize the sometimes complex mixtures of cyclic and acyclic ions formed from cyclopentanone and some of its alkyl derivatives. Use of a number of different techniques of ion structure characterization allowed corroboration of particular results by quite distinct methods and it also allowed the effects of ion internal energy and lifetime upon structure to be partly elucidated.