The Question of Cyclic Versus Acyclic Ions: The Structure of +. Gas Phase Ions

Article abstract of DOI:10.1002/oms.1210200109

The extent of isomerization of acyclic and cyclic gas phase radical cations of composition ^+. has been investigated by using collisionally activated dissociation spectroscopy.Both electron and charge exchange ionization were employed to form the ions with various internal energies.The ^+. ions investigated consisted of ionized phenylbutenes, ring-substituted methyl derivatives of allylbenzene and phenylpropene, 1-methyl-isopropenylbenzene, benzylcyclopropane, phenylcyclobutane, tetralin and 1-methylindan.The 1-methylindan and tetralin radical cations are the most stable of the C10H12 isomeric radical ions.The ^+. formed from acyclic olefins having the double bond in conjugation with the aromatic ring retain the initial structure to a significant extent.However, ions derived from olefins with the double bond out of conjugation with the benzene ring preferentially cyclize to stable five- and six-membered cyclic ions.Ring opening of small-ring cyclic ions, such as ionized benzylcyclopropane and phenylcyclobutane, occurs, followed by ring closure to the tetralin radical cation.