OHgruppen

OHGruppen, or hydroxyl groups, are a class of functional groups in organic chemistry consisting of an oxygen atom bonded to a hydrogen atom (-OH) and attached to a carbon skeleton (or to an aromatic ring in phenols). They are highly polar and can form hydrogen bonds, which influences solubility, boiling points, and reactivity.

OHGruppen occur in alcohols, phenols, and many biomolecules such as carbohydrates and amino acids. In aliphatic compounds they can be classified as primary, secondary, or tertiary depending on the number of carbon substituents bonded to the carbon bearing the -OH. Phenolic hydroxyl groups, attached to aromatic rings, have different acidity and reactivity compared with aliphatic alcohols.

The acidity of OHGruppen varies: typical aliphatic alcohols have pKa values around 15–19, while phenols are more acidic with pKa around 9–11. In water and biological contexts, hydrogen bonding involving OHGruppen underpins much of the structure and interactions of sugars, alcohols, and phenolic compounds.

Reactivity of OHGruppen includes deprotonation to form alkoxides, enabling nucleophilic substitution and ether formation. They readily undergo esterification with carboxylic acids to give esters, or with acid chlorides and anhydrides to form more reactive derivatives. Alcohols can be oxidized (primary to aldehydes then acids, secondary to ketones; tertiary generally resist oxidation). They can also be dehydrated under acidic conditions to form alkenes, with reaction outcome influenced by substitution level.

OHGruppen are widespread in chemistry and biology, from ethanol and phenol to sugars and many natural products, and they play a central role in solvent properties, metabolism, and synthetic transformations.