The oxidation half of the redox framing already appeared in the alcohols material; this track restores the reduction-overview framing so oxidation and reduction read as one paired system. In organic chemistry, oxidation = gain of bonds to O (or other heteroatoms) / loss of bonds to H, and reduction = gain of bonds to H / loss of bonds to O — a different bookkeeping than the electron-transfer definition from gen chem, and worth stating explicitly.

Arrange the common functional groups on a single oxidation-level ladder, most reduced to most oxidized: alkane → alcohol → aldehyde/ketone → carboxylic acid → CO₂. Moving down the ladder (toward alkane) is reduction; moving up is oxidation. The key reducing reagents students must distinguish by strength and selectivity:

NaBH₄ (sodium borohydride) — the mild reducer. Reduces aldehydes → primary alcohols and ketones → secondary alcohols, but is too weak to touch carboxylic acids or esters. Safe enough to use in protic solvents.
LiAlH₄ (lithium aluminum hydride) — the strong, non-selective reducer. Reduces aldehydes, ketones, carboxylic acids, esters, and amides all the way down to alcohols (or amines, for amides). It reacts violently with water, so it must be run in anhydrous conditions and quenched carefully.
Catalytic hydrogenation (H₂ / Pd, Pt, or Ni) — reduces C=C and C≡C (and can reduce other groups), adding H₂ across pi bonds; this is the bridge back to the alkene track.

The teaching point is selectivity: choosing NaBH₄ vs. LiAlH₄ lets a chemist reduce a ketone while leaving an ester intact, or reduce everything at once — a decision that recurs constantly in synthesis roadmaps.

"Up and Down"