Why does oxidising a primary alcohol give a different product than a secondary one?
Oxidation removes hydrogens from the C–OH carbon.
Oxidation removes hydrogens from the C–OH carbon. A primary alcohol has two H's there, so it oxidises first to an aldehyde and then to a carboxylic acid. A secondary alcohol has only one H there, so it stops at a ketone (which can't oxidise further without breaking C–C bonds). A tertiary alcohol has no H on that carbon at all, so it resists oxidation entirely.
Key point
1° → aldehyde → acid; 2° → ketone; 3° → no easy oxidation (H-count on the C–OH carbon).
Common mistake
expecting every alcohol to oxidise to an acid.
Memory tip
count H's on the C–OH carbon: 2 → acid, 1 → ketone, 0 → no reaction.
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