Unimolecular reactions of isolated organic ions: loss of carbon monoxide from the oxonium ion CH2CHCH2+OCH2via double hydrogen transfer

Abstract

The reactions of the metastable oxonium ion CH₂CHCH₂⁺OCH₂ have been investigated. This C₄H₇O⁺ species was generated by ionisation and alkyl radical loss from allyl ethyl or allyl propyl ether. CH₂CHCH₂⁺OCH₂ is apparently ideally suited to fragmentation via simple cleavage to form the favourable products CH₂CHCH₂⁺ and CH₂O. However, at low internal energies, expulsion of a neutral species having a mass of 28 amu takes place essentially to the exclusion of CH₂O loss. ²H-and ¹³C-labelling experiments reveal that it is carbon monoxide which is eliminated, via double hydrogen transfer between the developing products accessible to C–O bond fission. The role of ion–neutral complexes in these hydrogen transfer steps is discussed.