A mass spectral study of 1‐(aryldimethylsilyl)‐2‐propanones and their isomeric 2‐(aryldimethylsiloxy)‐1‐propenes

Abstract

AbstractThe mass spectra of a series of β‐ketosilanes, p‐YC6H4Me2SiCH2C(O)Me and their isomeric silyl enol ethers, p‐YC6H4Me2SiOC(CH3)CH2, where Y = H, Me, MeO, Cl, F and CF3, have been recorded. The fragmentation patterns for the β‐ketosilanes are very similar to those of their silyl enol ether counterparts. The seven major primary fragment ions are [MMe·]+, [MC6H4Y·]+, [MMe2SiO]+˙, [MC3H4]+˙, [MHCCCF3]+˙, [Me2SiOH]+˙ and [C3H6O]+˙ Apparently, upon electron bombardment the β‐ketosilanes must undergo rearrangement to an ion structure very similar to that of the ionized silyl enol ethers followed by unimolecular ion decompositions. Substitutions on the benzene ring show a significant effect on the formation of the ions [MMe2SiO]+˙ and [Me2SiOH]+˙, electron donating groups favoring the former and electron withdrawing groups favoring the latter. The mass spectral fragmentation pathways were identified by observing metastable peaks, metastable ion mass spectra and ion kinetic energy spectra.