Notably, the carboxylate analog, C6F13-CH2CH2-COO -(6:3 FTCA) showed different behaviors from 6:2 FTSA. A low oxidant dose at [S2O8 2-]:[6:3 FTCA]=10:1 achieved complete parent structure degradation for both SO4 -• and HO•. We attributed the much higher reactivity of FTCA than FTSA to the weaker C-H bond on the alpha carbon adjacent to the -COO -/-SO3 - group. However, we still cannot explain how this "local" structural difference caused vastly different levels of defluorination by SO4 -• (Table , zone G versus E). In the case of 6:3 FTCA, we observed an obvious shift of the PFCA product dominance from long-chain to shorter-chain when the S2O8 2-dose was raised. The rather consistent F atom balance (56-62%) and the increased deF% suggest the defluorination via decarboxylation and the subsequent chain-shortening of PFCA products by SO4 -•. Still, other pathways and mechanisms are responsible for the ~40% gap in F atom balance. For comparison, HO• oxidation of FTCA and FTSA showed very similar results in deF%, PFCA product distribution, and high F atom balance (Table , zone H versus F).