alkoxide ion
/ AL-kox-ide /
An alkoxide ion is what you get when you pluck the hydrogen off an alcohol's -OH group, leaving the oxygen with a negative charge: R-O-H becomes R-O(-). It is the conjugate base of an alcohol, exactly as hydroxide (HO-) is the conjugate base of water. Sodium ethoxide, CH3-CH2-O(-) Na(+), made from ethanol, is a workhorse example.
Because the negative charge sits on an electronegative oxygen but is not stabilised by anything else (no resonance, no extra electron-withdrawing groups), an alkoxide is a strong base — stronger than hydroxide — and an excellent, electron-rich nucleophile. To make one you treat the alcohol with a base strong enough to deprotonate it: an alkali metal (sodium or potassium added directly), or sodium hydride (NaH), which fizzes off hydrogen gas and leaves the alkoxide behind.
Alkoxides earn their keep as reagents. As nucleophiles they attack alkyl halides to forge ethers — that is the heart of the Williamson ether synthesis. As bases they pull off protons to drive E2 eliminations, and bulky ones like potassium tert-butoxide steer eliminations toward the less substituted (Hofmann) alkene. Whenever a reaction needs a strong, oxygen-based nucleophile or base that is itself organic, an alkoxide is often the answer.
Ethanol plus sodium metal: 2 CH3-CH2-OH + 2 Na -> 2 CH3-CH2-O(-) Na(+) + H2. The sodium reduces the O-H proton to hydrogen gas, leaving sodium ethoxide.
Deprotonate an alcohol and you get its conjugate base, the alkoxide.
An alkoxide is a stronger base than hydroxide, so you cannot make a meaningful amount of it with NaOH; the equilibrium lies the wrong way. Use a stronger base like NaH or the metal itself.