On the Mechanism of the Ethyl Elimination from the Molecular Ion of 6-Methoxy-1-Hexene

Article abstract of DOI:10.1002/oms.1210230513

It is shown by ¹³C and D labelling that the ethyl radical elimination from the molecular ion of 6-methoxy-1-hexene is a very complex process involving at least two different channels.The major channel (80percent) is induced by an initial 1,5-hydrogen shift in the molecular ion from C(5) to C(1) leading via a series of steps to methoxycyclohexane, which then undergoes a ring contraction to 2-methyl-1-methoxycyclopentane, being the key intermediate for the ethyl loss.The same key intermediate is formed in the other, minor channel (20percent) by ring closure directly following an initial 1,6-hydrogen shift in the molecular ion of 6-methoxy-1-hexene from C(6) to C(1).Collision-induced dissociation experiments on the ⁺ ion from 6-methoxy-1-hexene have further established that it has the unique structure of oxygen methyl cationized 2-methylpropen-2-al.This ion is also generated by ethyl loss from the molecular ion of 2-methyl-1-methoxycyclopentane itself, as shown by collision-induced dissociation experiments, thus confirming the key role of the intermediate mentioned.