Lactol



In organic chemistry, a lactol is a functional group which is the cyclic equivalent of a hemiacetal (\sCH(OH)O\s) or a hemiketal (>C(OH)O\s). The compound is formed by the intramolecular, nucleophilic addition of a hydroxyl group (\sOH) to the carbonyl group (C\dO) of an aldehyde (\sCH\dO) or a ketone (>C\dO).

A lactol is often found as an equilibrium mixture with the corresponding hydroxyaldehyde. The equilibrium can favor either direction depending on ring size and other conformational effects.
 * lactol equilibrium.png

The lactol functional group is prevalent in nature as component of aldose sugars.

Chemical reactivity
Lactols can participate in a variety of chemical reactions including:
 * Oxidation to form lactones
 * Reaction with alcohols to form acetals
 * The reaction of sugars with alcohols or other nucleophiles leads to the formation of glycosides
 * Reduction (deoxygenation) to form cyclic ethers