Determination of the double bond position in long-chain 6-alkenyl salicylic acids by collisional activation

The double bond position in long-chain 6-alkenyl salicylic acids has been determined by collisional activation of [M - H + 2Li]+ and [M - H]− precursor ions, which were generated by FAB. The pattern of product ions characteristic for charge-remote fragmentations allowed for a straightforward determination of the location of the double bond for the dilithiated precursor ion species, whereas complications from loss of CO2 were experienced for carboxylate anions. The product ion collisionally activated dissociation spectra obtained for both precursor ion species also reveal the formation of stable radical ions, which are likely distonic and point to the involvement of radical processes in charge-remote fragmentation.