Oxygen rearrangement on electron impact has been found to be an important fragmentation pathway in various (I-VII) cyclic ketones containing methoxyl and hydroxyl groups. This oxygen migration, which produces, for example, the m/e 60 ion (C2H4O2) from the molecular ion of 4-hydroxycyclohexanone (II), occurs in sixand seven-membered rings, with the two functional groups in both a 1,3 and 1,4 relationship. Heavy substitution around the ketone group appears to enhance the rearrangement while substitution adjacent to the hydroxyl or methoxyl group acts as a depressant. Deuterium labeling of 4-methoxy- and Δ5-hydroxycyclohexanone (I and II) suggested the intermediacy of the molecular ion of methyl As-hexenoate (XIII) in the case of 4-methoxycyclohexanone (I) and support for this proposal was provided by the synthesis of XIII. The rearrangement has been found to be unimportant in acyclic ketones containing primary methyl ether groups.
ASJC Scopus subject areas
- Colloid and Surface Chemistry