Lactol

In organic chemistry, a lactol is a functional group which is the cyclic equivalent of a hemiacetal (−CH(OH)O−) or a hemiketal (>C(OH)O−).

[1] 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.

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

Lactols can participate in a variety of chemical reactions including:[2]

The lactol functional group, highlighted in blue, is present in many sugars such as ribose shown here.