An alkoxide is the conjugate base of an alcohol, and therefore has an organic group bonded to a negatively charged oxygen atom. They are generally basic. Alkoxides, though generally not stable, are found as intermediaries in various reactions, including the Williamson ether synthesis reaction for forming ethers. Often alkoxides and sulfonates have more than one beta-carbon bearing a proton for base abstraction in E2. Favoring one proton for removal over others (regioselectivity) can be accomplished by choice of base.

Alkoxides can be produced by dissolving reactive metal, e.g. metallic sodium, into an alcohol. The alcohol acts as an acid, and hydrogen is produced:

R-OH + Na → R-O^– + Na⁺ + ½H₂

Despite the common misconception, this is not what happens when sodium hydroxide is added to an alcohol. Hydroxide is not a strong enough base to stoichiometrically deprotonate an alcohol. Alkoxides cannot exist but in trace amounts in water solutions due the acidity of water. Therefore, quantitative amounts of alkoxides must be dissolved in less acidic solvents, such as ethers.

Strongly basic organometallics such as organolithiums can also deprotonate an alcohol. Alkoxides can be used as bases to deprotonate ketones at the alpha position to produce enolates.

Alkoholaat