Crown Ether Donut Holes Serve Special Purposes

[caption id="attachment_23625" align="alignright" width="480"] Assorted Crown Ethers[/caption] Crown ethers are designer molecules – ring structures intended to serve specialized purposes. Each ring contains a number of ether linkages (-C-O-C-) that, based upon their structural formulas as they are drawn on paper, give the appearance of a royal crown. The “crowns” have different “sizes.” The most common crown ethers sport ethyleneoxy groups (-CH2-CH2-O-) joined end-to-end (making these structures oligomers), which are closed like a necklace. Ring properties and rigidity may be modified by means of appendages on the ring or other hetero atoms along the ring. Simple crown ether rings such as those shown in the figure lack rigidity because every bond is single. There are no multiple bonds reducing flexibility. Crown Ether Nomenclature For the most common crown ethers, there…
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