Two competing fragmentation processes in dimethoxybenzenes depending on their positional isomers: Elimination of CH3 and CHnO (n = 1–3) and formation of methoxycyclopentadienyl and protonated phenol ions

All the metastable transitions observed above m/z 39 in the first field-free region were compared for the three positional isomers of dimethoxybenzene. The observed isomer-dependent fragmentation processes, in particular the formation and decomposition of the m/z 95 (C₆H₇O)⁺ ion, are discussed in terms of two competing fragmentations elimination of CH₃ and CH_nO (n = 1–3) and formation of methoxycyclopentadienyl and protonated phenol ions] and the relative energies of several isomers of the C₆H₇O⁺ ion calculated with molecular orbital theory.