Chapter 16: Ethers, Epoxides and Sulfides
Oxygen atoms are capable of acting as Lewis bases due to the presence of the lone pairs (
in hydrogen bonding between water molecules or hydration of a metal ion in aqueous solution, see below).
The interaction with metal ions with ethers is also important:
In regular ethers, only weak complexes are formed.
However, in certain
(where mulitple interactions are possible) the complexes are much stronger.
hydration of a metal ion
These ethers are called "crown ethers" due to their shape.
They are based on repeating -
- units, derived from ethylene glycol :
indicates that there are 18 atoms in the ring, 6 of which are oxygen.
These compounds are important co-solvents.
of the cavity is
, whereas the
So a metal ion inside the cavity can be "carried" into an organic solvent.
This allows ionic systems such as KF to be dissolved in organic solvents and used as reagents where the metal ion is in a complex, but the anion is unsolvated or
and therefore quite reactive.
Varying the size of the crown ether varies the cavity size and some metal ions fit better than others.
For example, 18-crown-6 is an good fit for K+
In the crown ether 12-crown-4, how many atoms are there in the ring and how many are oxygen atoms ?
Where else have we talked about "naked" anions ?
Dr. Ian Hunt
, Department of Chemistry, University of Calgary