Computational calculations were performed to calculate the amount of negative charge on all oxygen atoms in the solvents prepared in this study. Results for all four molecules in this study are shown in Figure . These calculations reveal that the highest negative charges were always located on the phosphoryl O, regardless of PEG-arm length or butyl group branching. This negative charge was largest for (2) and was smallest for T i BP. The negative charges on the phosphoryl O of all the solvent molecules are very close, and the small differences of charges in molecules (1) -( ) could be attributed to the vicinity atoms of phosphoryl O in the optimized structures. The charges on the O atoms in the PEG arms tended to decrease with distance removed from the phosphoryl group. In ( ) and ( ) the charges consistently decreased away from the phosphoryl group, whereas in (3) they were slightly elevated at the two internal etheric O atoms. For all three phosphate esters, the lowest negative charges for all O atoms in all molecules were consistently located at the terminal methoxy O atom. These results suggest that the phosphoryl group is the most likely location for interaction with CO2, even when PEG groups are present.