The density and viscosity was measured for more mixtures, but Table only shows the twenty mixtures with water content < 1.5% w/w (Table in supporting information). The densities at 293 K range from 0.918-1.18 g/mL. Because of the variation in molar ratios and water content, it is difficult to compare densities across all of the mixtures. However, several mixtures have the same ratio, same HBD, and differing HBA, which may be useful to compare. For example, the density is higher for TBABr vs. TBACl mixtures (1:2 TBABr vs. TBACl: (+)-diethyl-L-tartrate and 1:2 TBABr vs. TBACl: dimethyl-D-malate), which could be the result of the lower water content in the TBABr mixtures.