Bifunctional even‐electron ions. III. Fragmentation behaviour of aliphatic hydroxonium ions containing an additional carbomethoxy group

The primary and subsequent fragmentations of the bifunctional oxonium ions \documentclass{article}\pagestyle{empty}\begin{document}${\rm R} \!-\! \mathop {\rm C}\limits^ + ({\rm OH})\! -\! ({\rm CH}_2)_n \! - \! {\rm COOCH}_3 $\end{document} ( n = 0−5), a , are dominated by functional group interactions. Loss of CH 3 OH is the only appreciable primary fragmentation of the higher homoiogues, but for the lowest homologue ( a 0 ) this reaction is missing. Instead, CO loss is observed. The next homologue ( a 1 ) shov.s loss of CH 2 CO besides loss of CH 3 OH. The mode of the subsequent fragmentations is dependent on the chain length separating the functional group, and formation of cyclic ions is typical of the fragmentation behaviour of a 2 and a 3 . Evidence for proton transfer from the carbonyl oxygen to the methoxy group of a protonated ester group is presented.