Hemiaseetaliryhmä

Hemiaseetaliryhmä refers to a specific functional group in organic chemistry. It is characterized by a carbon atom that is bonded to one alkoxy group (-OR), one hydroxyl group (-OH), and two other carbon atoms. This structure is an intermediate in the formation of acetals from aldehydes or ketones and alcohols. The hemiacetal group is formed when one molecule of alcohol adds to the carbonyl group of an aldehyde or ketone. This reaction is reversible and is typically catalyzed by an acid. In aqueous solution, hemiacetals are in equilibrium with the parent aldehyde or ketone and alcohol. The hemiacetal group is less stable than the acetal group, which is formed by the further reaction of a hemiacetal with another molecule of alcohol, where both hydrogen atoms of the hydroxyl group are replaced by alkoxy groups. Hemiacetals are important in carbohydrate chemistry, where many cyclic sugars exist in equilibrium between their open-chain aldehyde or ketone form and their cyclic hemiacetal form.