ether
/ EE-ther /
An ether is a molecule in which an oxygen atom bridges two carbon groups: R-O-R'. Think of water with both its hydrogens replaced by carbon chains. The classic example, diethyl ether (CH3-CH2-O-CH2-CH3), was the surgical anaesthetic of the nineteenth century and is still a common laboratory solvent.
The defining trait of ethers is their chemical inertness. The oxygen has no O-H bond to react, its lone pairs make it only weakly basic, and the C-O-C linkage is strong and stable. Ethers shrug off bases, mild acids, oxidising agents, reducing agents, and nucleophiles — almost everything a chemist might throw at the molecules dissolved in them. This is exactly why they make superb solvents: diethyl ether and THF (tetrahydrofuran, a cyclic ether) dissolve a wide range of organic compounds while staying out of the reaction themselves, and they are essential for handling reactive species like Grignard reagents.
Their unreactivity also makes ethers ideal protecting groups. If you have a sensitive -OH that would interfere with a planned reaction, you can convert it temporarily into an ether (for instance a silyl ether or a benzyl ether), run your chemistry safely while the oxygen sits protected and inert, then remove the protecting group afterward. Ethers are not entirely bulletproof, though: they cleave under strong acid (especially HI or HBr), and on long standing in air they slowly form explosive peroxides — a genuine safety hazard with old bottles of diethyl ether.
Diethyl ether, CH3-CH2-O-CH2-CH3, and THF (a five-membered ring with one oxygen) are everyday lab solvents — chosen precisely because they dissolve reagents without reacting with them.
An oxygen bridging two carbons — inert, which is exactly why ethers are great solvents.
Ethers are unreactive, not utterly inert: old bottles can build up explosive peroxides on standing in air, and strong acids like HI cleave them — so do not treat an ether as totally bulletproof.