Fragmentation of acylium ions from methyl levulinate. Isomerization processes involving carbon and oxygen atoms of both carbonyl groups
作者:M. Corval、A. Harrata、J-P. Morizur
DOI:10.1002/oms.1210241102
日期:1989.11
AbstractThe fragmentations of the acylium ions OC+CH2CH2CO2CH3 and OC+CH2CH2COCH3 generated from methyl levulinate are governed extensively by the interaction of the two carbonyl groups. Both species eliminate a molecule of CO unimolecularly and under CID conditions. The results derived from measurements of 13C and 18O labelled precursors, together with kinetic energy release values, have been used to study the mechanisms. In the first of these acylium ions, both carbonyl groups are equivalent; this phenomenon can be the result of a 1,4 methoxy shift. In the second acylium ion, only the oxygen atoms change their positions; this isomerization occurs via the [MH]+ of γ‐valerolactone. Some other fragmentation processes also discussed in relation to 2H labelling are the formation of the [M COOCH3] + ion and the loss of HCOOCH3 in the collision‐induced dissociation mass spectra of the first acylium ion, and the formation of the [CH3CO]+ ion and the loss of H2O for the second one.
Deuterated analogues of the free radical trap DEPMPO: synthesis and EPR studies
Three analogues of 5-diethoxyphosphoryl-5-methyl-1-pyrroline N-oxide (DEPMPO, 1) labelled with two (1-d2), five (1-d5) or seven (1-d7)
2H were synthesized and used to trap the tert-butylperoxyl radical. The EPR spectra of 1-d2-OOBut and 1-d7-OOBut spin adducts exhibited more straightforward patterns and better signal to noise ratio than those obtained with 1 or 1-d5. The use of the easily available 1-d2 as spin trap could help significantly the analysis of the EPR signals when the signal of either superoxide or alkylperoxyl spin adduct is superimposed with the signals of other spin adducts.