The anion appears to be the one of the most important factors when selecting an ionic liquid for the capture of CO2. Experiments have also shown that the anion has the ability to re-protonate due to water content in the system, which would limit CO2 binding. To further examine this issue the binding enthalpies have been studied for a variety of anions that include two or three nitrogens in the bicyclic structure. A trend was found between the binding of CO2 and the proton affinity to determine which anion would be most successful at binding CO2 while not binding a proton. Five-member rings showed a greater performance to CO2 binding, when compared to the six membered side of the structure. A positive correlation was also observed between the charge of the CO2 in the system and the bond length associated with CO2 binding to a nitrogen site on the anion.