Draw the cyclic hemiacetal that is formed when each of the

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In this multi-part exercise set, we’re asked to draw the cyclic hemiacetal that is formed when each of the following bifunctional compounds is treated with aqueous acid.

Recall that the carbonyl carbons of aldehydes/ketones are electrophilic. If the aldehyde/ketone oxygen is protonated (using acidic catalysis), the electrophilicity is greatly increased. The carbonyl carbon can then be attacked by nucleophiles that might be present, such as hydroxyl groups. In the case of hydroxyaldehydes or hydroxyketones, the hydroxyl group is present in the same molecule as the protonated carbonyl.

The hemiacetal formation, therefore, takes place in an intramolecular fashion, which closes up a ring.