Mass spectrometric study of gamma-aryl-alpha, gamma-diethoxy-alpha, beta-butenolides

Electron impact mass spectra of eight of the title compounds are reported. Abundant fragment ions were produced under electron impact (EI) conditions and, with one exception, the (ArC = O+) ions were the base peaks. The EI fr agmentation mechanisms of two representative compounds were studied with th e aid of high-resolution and mass-analyzed ion kinetic energy spectrometry (MIKES) data. The M+ ions fragment to give both an odd-electron ion and an even-electron fragment ion, Two H-atom rearrangements proceeding via four-m embered ring intermediates and three losses of CO through i- and alpha-frag mentations were observed under EI, On comparing fragmentations under EI con ditions with those under FAB conditions for two of the compounds, the fragm entation mechanisms were reasonably similar, with additional fragmentations rationalized in terms of the ionization proton being located on the oxygen atom of the beta-ethoxy group. Copyright (C) 2000 John Wiley & Sons, Ltd.