Nature of methyl cation bonding to dihydroxybenzenes elucidated using an ion trap mass spectrometer

Methylation of the isomeric dihydroxybenzeres using the dimethylfluoronium ion ([CH3FCH3]+) was studied in a quadrupole ion trap mass spectrometer. The products were characterized by tandem mass spectrometry using collision‐activated dissociation. A comparison of the daughter ion spectra of the methylated products with those of model ions, generated by protonation of substituent‐ and ring‐methylated analogs, demonstrates that a mixture of methylated products is generated. Included are structures in which the methyl is σ‐bonded to the ring and others with σ‐bonds to the heteroatom, the latter being favored in catechol and hydroquinone. The energy‐resolved daughter ion spectra for the methylated isomers, acquired by varying the amplitude of the a.c. voltage used to excite resonantly the mass‐selected ions, support these conclusions regarding the site of methylation.