lactol

{{short description|Functional group >C(OH)O– on a cyclic compound}}

File:Lactol group in ribose.png shown here.]]

In organic chemistry, a lactol is a functional group which is the cyclic equivalent of a hemiacetal ({{chem2|\sCH(OH)O\s}}) or a hemiketal ({{chem2|>C(OH)O\s}}).

The compound is formed by the intramolecular, nucleophilic addition of a hydroxyl group ({{chem2|\sOH}}) to the carbonyl group ({{chem2|C\dO}}) of an aldehyde ({{chem2|\sCH\dO}}) or a ketone ({{chem2|>C\dO}}).IUPAC Gold Book [http://goldbook.iupac.org/L03438.html lactols]

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.

:File:lactol equilibrium.png{{-}}

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