ethers

Meaning: An ether has an oxygen bonded to two carbon groups, R–O–R′, where R and R′ are alkyl or aryl. The oxygen is sp³ with a bent C–O–C geometry, so the molecule is weakly polar. It has no O–H bond, so ethers cannot hydrogen-bond to each other, but the oxygen lone pairs can accept hydrogen bonds from water. Ethers do not react with bases, mild oxidants or reducing agents, so diethyl ether and THF are common solvents.

On the MCAT: Boiling points follow alcohol > ether > alkane of similar molar mass, because only the alcohol hydrogen-bonds to itself. Synthesis: the Williamson ether synthesis is an SN2 reaction of an alkoxide (RO⁻) with a methyl or primary alkyl halide (R′–X) to give R–O–R′. A bulky secondary or tertiary halide gives elimination instead. Cleavage: strong acid such as HBr or HI protonates the oxygen, making it a leaving group, and the products are an alkyl halide and an alcohol. Epoxides are three-membered cyclic ethers; their ring strain makes them reactive toward nucleophiles.

Common confusion: Ethanol and dimethyl ether (both C₂H₆O) are constitutional isomers, but ethanol boils much higher because it has an O–H bond. Also, "unreactive" applies to open-chain ethers; strained epoxides open easily.