NaOH

Meaning: NaOH is ionic, and in water it supplies OH⁻ with Na⁺ as a spectator ion. OH⁻ is both a strong nucleophile and a strong base. As a nucleophile it attacks the carbonyl carbon of esters (saponification) and, with heating, amides. It can also displace a leaving group from an unhindered alkyl halide by SN2 to give an alcohol. As a base it removes a proton: it triggers E2 elimination of alkyl halides (favored by heat and by secondary or tertiary substrates), converts carboxylic acids and phenols to their salts, and forms enolates in aldol reactions.

Equation: RCOOR′ + OH⁻ → RCOO⁻ + R′OH. R and R′ are alkyl groups (no units); Na⁺ is a spectator and is left out.

On the MCAT: You may be asked to predict the product when NaOH meets an ester, alkyl halide or acid. Extraction is also common. Aqueous NaOH turns carboxylic acids and phenols into water-soluble sodium salts, so they move to the aqueous layer while neutral compounds stay in the organic layer. Adding strong acid later regenerates the neutral acid.

Common confusion: Students assume NaOH gives substitution. With tertiary halides, or with heat, elimination wins. Saponification is also not reversible in base, because the carboxylic acid formed is deprotonated to a carboxylate that does not react with the alcohol. Acid-catalyzed ester hydrolysis is an equilibrium.