oxidation

Meaning: Oxidation is the loss of electrons, seen at carbon as more bonds to oxygen (or another more electronegative atom) or fewer bonds to hydrogen. The oxidizing agent is the species that gets reduced. Carbon oxidation levels rise in this order: alkane, alcohol, aldehyde or ketone, carboxylic acid, CO₂.

On the MCAT: You are usually given a substrate and a reagent and asked for the product. PCC oxidizes a primary alcohol to an aldehyde and stops there. Strong oxidants such as CrO₃ in aqueous acid (Jones), K₂Cr₂O₇ or KMnO₄ carry a primary alcohol on to the carboxylic acid. Secondary alcohols give ketones with either type of reagent. A tertiary alcohol has no hydrogen on the carbon bearing the OH, so it does not oxidize under these conditions. Passages may also ask you to rank compounds by oxidation level, or link the idea to biochemistry, where an alcohol is oxidized while NAD⁺ is reduced to NADH.

Common confusion: Many students define oxidation as adding oxygen, then miss cases such as an alcohol becoming a ketone, where the carbon loses a C–H bond, or an alkane becoming an alkyl halide. Count bonds from carbon to more electronegative atoms instead. Oxidation never happens alone: whatever is oxidized is paired with a reagent that is reduced.