Mass spectrometric studies.  I.  Fragmentation of methyl cyclohexyl ether

It is shown by 13C and D labelling that the ethyl radical elimination from the molecular ion of Bmethoxy-1-hexene is a very complex process involving at least two different channels. The major channel (80%) is induced by an initial 1,lhydrogen shift in the molecular ion from C(5) to C(l) leading via a series of steps to methoxycyclohexane, which then undergoes a ring contraction to 2-methyl-l-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,bhydrogen shift in the molecular ion of bmethoxy-1-hexene from C(6) to C(1). Collision-induced dissociation experiments on the [Methyl] + ion from 6-methoxy-1-hexene have further estab-lished 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.

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“…6-Methoxy-1-hexene (l), 4,4-dideutero-6-methoxy-l-hexene (lf), and methoxycyclohexane (2). These were available from earlier studies.'…”

Section: Preparation Of Compoundsmentioning

confidence: 99%

On the mechanism of the ethyl elimination from the molecular ion of 6‐methoxy‐1‐hexene

Molenaar-Langeveld

Fokkens

Nibbering

1988

Org. Mass Spectrom.

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“…Methyl cyclohexyl ether, for example, undergoes hydrogen abstraction to the extent of 8% from C-2 and C-6, 66% from C-3 and C-5, 23% from C-4, and 84% from C-3, C-4, and C-5 combined; the assumption of an isotope effect of K0/KH = 0.9 removes the discrepancy between these last two values. 131 The loss of methanol from the methyl ethers of various diols and polyols has been investigated.74'75•132""134 Loss of methanol occurs readily from the dimethyl ether of propane-1,3-diol, but the extent of methanol loss decreases as the separation between the methoxy groups increases. Triand tetramethoxy alkanes also lose methanol quite readily, as might be expected.132 In the case of the various dimethoxycyclohexanes, methanol loss is least significant for the 1,2isomer, presumably because of a more favorable pathway in SCHEME XVI the case of this isomer to the ion at m/e 84 (Scheme XVI).…”

Section: Loss Of Alcohols a Loss Of Alcohols From Ethersmentioning

confidence: 99%