Binding data in methanol are given below for a series of interactions between crown ethers 3-6 and cations. 3 5 6 Log K (Li*) = 0.5 Log K (Na*) = 1.73 Log K (K*) = 0.86 Log K (Li") = 1.42 Log K (Na*) = 3.42 Log K (K*) = 3.38 Log K (Na*) = 4.32 Log K (K*) = 6.10 Log K (Cs*) = 4.62 Log K (K*) = 4.41 Log K (Cs*) = 5.02 (i) suggest an explanation for the selectivities observed for the binding of 18-crown-6 5 towards cations (ii) suggest an explanation as to why the binding of cations to the different sized crown ethers might not fully follow the predicted trend