Radical cation adduct formation between dihydroxybenzenes and ammonia under CI conditions

Abstract

AbstractUnder ammonia chemical ionization conditions, instead of the expected [M + H]+, and [M + NH4]+ and [M + N2H7]+ ions, hydroquinone gives rise to M+·, [M + NH3]+· and [M + 2NH3]+· ions, whereas resorcinol gives both series of ions. Catechol shows M+·, [M + NH3]+·, [M + NH4]+ and [M + N2H7]+ ions. The favourable ionization energy difference between ammonia and the dihydroxybenzenes leads to charge exchange and the resulting radical cations, being highly acidic, form clusters with the NH3. The effect of ion source parameters and mass‐analysed ion kinetic energy (MIKE) and collisional activation spectra confirm proton‐bound structures for [M + NH3]+· and [M + 2NH3]+ ions. Because of the proximity of the two OH groups, NH4+ attachment is favoured in catechol. The MIKE spectra of [M + H + Et2O]+ ions show that resorcinol has the highest proton affinity among the dihydroxybenzenes.