hüdroksüüli

Hüdroksüüli (chemical formula –OH) is a functional group composed of an oxygen atom bonded to a hydrogen atom. It is one of the most fundamental and widely occurring groups in organic chemistry, playing a crucial role in defining the properties of many compounds. The term originates from the Latin *hydroxylum*, meaning "hydroxyl," derived from *hydro-* (water) and *-xyl* (wood or related to oxygen).

Hydroxyl groups are polar, meaning they have an uneven distribution of electron density, which influences the solubility and reactivity of molecules containing them. Compounds with hydroxyl groups are classified as alcohols if they are attached to carbon atoms (e.g., methanol, ethanol) or phenols if they are bonded to aromatic rings. Carboxylic acids contain both a hydroxyl group and a carbonyl group (–COOH).

The presence of hydroxyl groups affects physical properties such as boiling points, as hydrogen bonding between molecules increases intermolecular forces. This is why alcohols have higher boiling points than similar non-polar compounds. Hydroxyl groups also contribute to the acidic nature of certain compounds, particularly in carboxylic acids, where the hydrogen of the –OH group can dissociate in solution.

In biochemistry, hydroxyl groups are essential in biological molecules like sugars (e.g., glucose) and amino acids (e.g., serine). They participate in enzymatic reactions, metabolic pathways, and structural roles within biomolecules. Additionally, hydroxyl radicals (·OH), highly reactive species, play significant roles in oxidative stress and environmental chemistry, contributing to processes like atmospheric pollution and aging.

Synthetic applications of hydroxyl groups include the production of solvents, plastics, and pharmaceuticals. They are also involved in polymerization reactions, where hydroxyl-containing monomers form polymers like polyesters. The reactivity of hydroxyl groups makes them versatile intermediates in organic synthesis.