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A famous experiment which changed organic chemistry: purple benzene. 

Crown ethers are an unusual series of molecules that have the ability to complex small cations, notably alkali metals such as lithium, sodium and potassium. These cyclic molecules, upon complexing a cation, can allow a salt to go into organic solvent that otherwise wouldn’t. This makes reactions that are otherwise impossible accessible.

Charles John Pedersen (October 3, 1904 – October 26, 1989) was a pioneer of this field of chemistry. He was an American organic chemist best known for describing methods of synthesizing crown ethers.  He shared the Nobel Prize in Chemistry in 1987 with Donald J. Cram and Jean-Marie Lehn.

A good example is how 18-crown-6 (shown above) can help potassium permanganate (a beautiful purple oxidizing agent based on manganese (VII)) go into organic solvent. Normally, you can only get permanganate into very polar solvents (as seen on the first pics where the benzene dissolves 0% of the permanganate), but when adding 18-crown-6, it allows the permanganate ion to go into solution as well forming a beautiful purple solution as seen above.

An inspiring article, what is worth to read about crown ethers, by Charles J. Pedersenhttp://pubs.acs.org/doi/abs/10.1021/ja01002a035