Lactol

Lactols are cyclic hemiacetals by IUPAC, being understood by IUPAC under hemiacetals also hemiketals. Lactols therefore intramolecular addition products of a hydroxy group to an aldehyde group or keto group.

They are mainly in carbohydrates ( saccharides ) are of importance. These are some monosaccharides such as aldoses and ketoses. In this case ( five rings ) or pyranose form according to the ring size furanoses (Six Rings ).

Balance between open-chain and ring form

In aqueous solution, monosaccharides are in equilibrium between the open chain and hemiacetal, wherein the cyclic form is almost always stable. When fructose analogue 4- hydroxybutanal are about 11.4 % in the open-chain and 88.6 % present in the furanose form. Wherein the glucose, the equilibrium lies to 99.9974 % on the pyranose side, while the analogue of 5 - hydroxypentanal occurs to 6.1% in the open-chain and 93.9 % in the hemiacetal form.