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The role of hydrogen migration in the mechanism of alcohol elimination from MH+ ions of ethers upon chemical ionization

✍ Scribed by Morlender-Vais, N.; Mandelbaum, A.

Publisher
John Wiley and Sons
Year
1997
Tongue
English
Weight
504 KB
Volume
32
Category
Article
ISSN
1076-5174

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✦ Synopsis

An enhanced elimination of alcohol under isobutane CI conditions, resulting in highly abundant [ MH Ô ROH ] ' ions, has been observed in several primary and secondary ethers having a tertiary b-position (methine), as compared with those with b-methylene. This elimination exhibits a signiÐcant degree of stereospeciÐcity in stereoisomeric 2-methyl-1-methoxycyclohexanes 4 and 1-methoxy-trans-decalins 7, a †ording more abundant [ MH Ô ROH ] ' ions in the cis isomers 4c and 7tc than in their trans counterparts 4t and 7tt. These Ðndings suggest involvement of a 1,2-hydride migration from the b-to a-position in the course of the alcohol elimination from the MH' ions of the above cis-ethers, resulting in tertiary carbocation structures. The proposed mechanism of alcohol elimination is supported by a considerable deuterium isotope e †ect detected in b-deuterium-labeled cis-2-methyl-1methoxycyclohexane and by a CID study of the structures of [ MH Ô ROH ] ' ions obtained from cisand trans-1,2-dialkoxycyclohexanes. Ring contraction by a Meerwein-type rearrangement has also been observed in the latter system.

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