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In acid-catalyzed hydration, protonation creates a carbocation that water attacks. The reaction follows Markovnikov orientation, but the intermediate can rearrange, and its planar structure means the stereochemical outcome is not specific. Oxymercuration–demercuration also gives Markovnikov alcohols, while avoiding carbocation rearrangements through a bridged mercurinium intermediate. Hydroboration–oxidation instead gives anti-Markovnikov hydration with syn addition and no carbocation rearrangement pathway. Comparing these methods means considering both where the OH group ends up and how it is introduced. The full lesson develops these distinctions through mechanisms, a comparative summary, and kinetic and synthetic considerations.