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Eur. J. Mass Spectrom. 2, 233 - 246 (1996) |
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The mechanism of alkyl radical elimination from ionised gg-disubstituted alkenyl methyl ethers | ||
Richard D. Bowen and Paul Clifford |
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ABSTRACT: | ||
The mechanism of alkyl radical loss from ionised alkenyl methyl ethers containing two g-alkyl substituents, R1R2C=CHCH2OCH3+·, has been studied by investigating the collision-induced dissociation spectra of the resultant CnH2n1O+ oxonium ions (n = 57). Comparison of these spectra with one another and those of reference ions generated by dissociative ionisation of secondary allylic alkenyl methyl ethers indicates that expulsion of a g-alkyl group occurs without isomerisation of the heavy atom skeleton via an allylic rearrangement. This finding is consistent with the occurrence of two consecutive 1,2-H shifts in R1R2C=CHCH2OCH3+·, followed by g-cleavage of the ionised enol ether, R1R2CHCH=CHOCH3+·, to give R1CH=CHCH=OCH3+ or R2CH=CHCH=OCH3+. Thus, CH3CH2CH2(CH3CH2)C=CHCH2OCH3+· loses C2H5· and C3H7· to yield CH3CH2CH2CH=CHCH=OCH3+ and CH3CH2CH=CHCH=OCH3+, respectively. | ||
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