Radical processes in remote charge fragmentations of lithium-cationized long-chain alkenyl and alkadienyl salicylic acids

Multistep radical processes are proposed to rationalize the formation of product ions formed by collisionally induced and spontaneous fragmentation of lithium-cationized 6-alkenyl and 6-alkadienyl salicylic acids. An important step in these processes consists of a homolytic CH cleavage, a mechanism which is consistent with the charge-remote concept. Evidence is given by the observation that the fragmentation of ions formed by the loss of a hydrogen radical is similar to that found for the precursor [M − H + 2Li]+ ions. The proposed mechanisms also explain very well the observed enhanced abundances of ions whose formation involves formal benzylic, homo-benzylic and homoallylic cleavages. The enhanced abundance of ions whose formation involves formal allylic cleavages can be readily rationalized by resonance stabilization of intermediate allylic radical ions.