Reactions of ionised methyl pent-4-enyl ether, CH2CH(CH2)3OCH3·+11Dedicated to Professor Nico Nibbering on the occasion of his imminent retirement in recognition of his outstanding contributions to gas-phase ion chemistry.

The reactions of CH2CH(CH2)3OCH3·+ are reported and discussed, with particular emphasis on the behaviour of the metastable ions. The main reactions of the low energy title ions are elimination of CH3·, C2H5·, and CH3OH, each occurring at similar rates; but loss of H2O, H· and, to a lesser degree, C2H4, also occurs. The mechanisms of these reactions have been probed by examining collision-induced dissociation spectra and by extensive D-labeling experiments. The site selectivity for the three main reactions and water elimination varies considerably. Thus, metastable CH2CH(CH2)3OCD3· expels almost exclusively CH3· (>97% selectivity) and mainly C2H5· and CD3OH (∼90% selectivity); but H2O (∼37%), HOD (∼53%), and even D2O (∼10%) all occur in water loss. Tentative mechanisms are proposed for these processes, several of which must entail extensive hydrogen transfers and skeletal isomerisations. Loss of C2H5· and CH3· appear to involve rearrangements to species accessible to ionised cyclopentyl methyl ether, but expulsion of CH3OH and H2O do not.