The structure of ionized 1,5 hexadiene in the gas phase

The structure of ionized 1,5-hexadiene, prepared by charge transfer between 1,5-hexadiene and CS2+, is examined using energy-resolved collision-induce d dissociation (CID). By comparing the product distributions and product ap pearance curves with those of authentic low-energy C6H10+ ions, it is deter mined that 1,5-hexadiene cation spontaneously rearranges to cyclohexane cat ion in the gas-phase. The proposed mechanism for formation of cyclohexane c ation in the gas-phase. The proposed mechanism for formation of cyclohexene cation in the gas phase is analogous to that determined for this process u nder matrix isolation conditions, where it proceeds; via a Cope rearrangeme nt to the cyclohexane-1,4-diyl cation, followed by isomerization to cyclohe xene cation. It is shown that electron ionization (EI) of 1,5-hexadiene giv es a different molecular ion than is obtained upon chemical ionization (CI) . The energy-resolved CID mass spectrum for the EI product is consistent wi th what would be obtained for a mixture of low energy ion isomers. (C) 2001 American Society for Mass Spectrometry.