Further Investigation of the Mass Spectrum of Isopropyl o-Toluate

Abstract

The formation of an [M+1]⁺ ion and the fragmentation of isopropyl o-toluate have been further investigated by measuring the mass spectrum of CD₃C₆H₄COOC₃H₇(d₃). The hydrogen atom, which is involved in the [M+1]⁺ ion formation, originates mainly from the three methyl groups in the molecule, in contrast to the previous conclusions.
In the intermediate ion at m/z 136, [C₈H₈O₂]⁺, almost complete scrambling of the hydroxyl hydrogen atom with the methyl hydrogen atoms in tolyl group, not with the hydrogen atoms in benzene ring, takes place prior to the elimination of a water molecule from this m/z 136 ion. However, any hydrogen exchange reaction does not occur prior to the elimination of a hydroxy radical, which is a competing reaction with water loss, from the m/z 136 ion.
Furthermore, it is shown that the metastable decomposing [C₇H₇]⁺ ion at m/z 91 isomerizes to tropylium ion prior to the decomposition of this ion into the [C₅H₅]⁺ ion at m/z 65.