Q15P - Organic Chemistry (Mcmurry)

Question

15-Crown-5 and 12-crown-4 ethers complex Na⁺ and Li⁺, respectively. Make models of these crown ethers, and compare the sizes of the cavities.

Step-by-Step Solution

Answer

Answer

Step-by-Step Solution Step 1: Crown ethers

Crown ethers are giant molecules belonging to the ether family. They are named in a general formate x-Crown-y, where x is the total number of atoms present in the ring and y is the number of ether oxygen atoms. The cations bind in the center of the ring by ether oxygen atoms.

Step 2: Models of crown ethers

15-Crown-5 ether complex Na⁺ is a 15-membered ring containing 6 ether oxygen atoms. It binds strongly with Na⁺  ion present at the center of the ring.

12-Crown-4 ether complex Li⁺  is a 12-membered ring containing 4 ether oxygen atoms. It binds strongly with Li⁺ ion present at the center of the ring.

                 Models of crown ethers

Step 3: Size of the cavities

Based on ionic radii, in 15-Crown-5, the ion-to-oxygen distance is about 40% longer than that of 12-Crown-4 because the ring size is bigger in 15-Crown-5.