GC/MS/MS studies of unusual chemical ionization (CI) processes with a triple stage quadrupole (TSQ) mass spectrometer

Abstract

For 2,2,6,6-tetramethylcyclohexanone (I), the CI(CH 4)-induced fragmentation of MH + into Me 2C=O N + H and [MH - H 2O] + ions is shown to proceed through common intermediates via two interconnected paths. Route A (ca. 75% of either fragment ion current/ involves sequential [1,2]-methyl migration, ring contraction and double [1.2]-methyl migration, route B (ca. 25%) may proceed via [1,2]-methyl migration, [1,21-hydroxyl migration, ring contraction and double [1,2]-methyl migration. A study of the effect of methyl substitution on the relative ease of these routes by GC/MS/MS analysis of mixtures of the lower methyl homologues of I sheds additional light on the mechanisms.