Breslow intermediates play crucial roles in both umpolung and redox reactions in N-heterocyclic carbene catalysis. Compared to the well-known nucleophilic character, the electronic structure of Breslow intermediates on the radical route is still unclear. We investigate the potential energy surfaces with high-level ab initio methods for four typical Breslow intermediates in both of their enol and enolate forms. In the enol form, high energies of around 60 kcal/mol to the Rydberg-like states and those higher than 120 kcal/mol to remove an electron demonstrate that the enol Breslow intermediates tend not to generate radicals unless strong oxidants are present. The low-lying dipole-bound states and small electron detachment energies in the enolate form in contrast show that the enolate Breslow intermediates are possible precursors to radicals. More importantly, metastable dipole-bound states exist in the imidazole- and the triazole-based enolate Breslow intermediates. Energies to detach one electron of several enolate Breslow intermediates reveal that the bulky and electron-withdrawing groups stabilize the singlet ground states, which explains that the utilization of such substituents can lead to successful isolation for Breslow intermediates in experiments.