Xiaoran He

Electron impact fragmentation mechanisms of some cyclic esters with helical structures

The electron impact mass spectra of several cyclic esters with helical structures have been studied. Their fragmentation pathways were proposed and confirmed by mass-analyzed ion kinetic energy (MIKE) and high-resolution data. In general, the dominant fragmentation pathways in the spectra of these compounds originate from a alpha-cleavage with loss of a hydrogen or methyl group. The difference between hydrogen and methyl group loss greatly affects the subsequent fragmentations. Although, due to their helicity, these cyclic esters are optically active no stereo-related fragmentation pathway was observed. Copyright 2000 John Wiley & Sons, Ltd.

Mass spectrometric study of six cyclic esters

A series of cyclic esters, which are optically active as a consequence of their helical structures, were synthesized to investigate the relationships between their structures and their optical activities. This paper reports the electron impact fragmentation mechanisms of these six cyclic esters. Accurate mass measurements and mass analyzed ion kinetic energy spectrometry confirmed fragmentation patterns. The stability of the fragment ions has a great influence on the fragmentation pathways, but no correlation with the optical activity was found.

Mass spectrometric study on methyl 5-methyl-2-oxo-3-[2-(4-R-phenyl)-1-ethyl]cyclopentanecarboxylates and methyl 2-oxo-5-(4-R-phenyl)-3-propylcyclopentanecarboxylates

The mechanisms of mass spectrometric fragmentation of eight new compounds, including methyl 5-methyl-2-oxo-3-[2-(4-R-phenyl)-1-ethyl]cyclopentanecarboxylates (Group I, R = substituent) and methyl 2-oxo-5-(4-R-phenyl)-3-propylcyclopentanecarboxylates (Group II, R = substituent), were studied using mass analyzed ion kinetic energy spectrometry. The chemical compositions of these compounds and some of their important fragment ions were verified by high-resolution MS data. There were two types of H-rearrangement as regards the route of fission. In one type, the γ-H migration was influenced by both the electron effect and the steric hindrance of substituents, whereas on the other α-H migration losing methanol was due to the α-position active hydrogen located between two carbonyls, and this was verified by the method of deuterium labelling.