摘要:
AbstractIt 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 (80%) is induced by an initial 1,5‐hydrogen shift in the molecular ion from C(5) to C(l) leading via a series of steps to methoxy‐cyclohexnne, 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 (20%) 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(l). Collision‐induced dissociation experiments on the [M − ethyl]+ ion from 6‐methoxy‐1‐hexene have further established that it has the unique structure of oxygen methyl cationized 2‐methyIpropen‐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.