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On the mechanism of the ethyl elimination from the molecular ion of 6‐methoxy‐1‐hexene
Author(s) -
MolenaarLangeveld Tineke A.,
Fokkens Roel H.,
Nibbering Nico M. M.
Publication year - 1988
Publication title -
organic mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 0030-493X
DOI - 10.1002/oms.1210230513
Subject(s) - dissociation (chemistry) , chemistry , polyatomic ion , ion , hydrogen , photochemistry , organic chemistry
It is shown by 13 C 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.