karboksyl

Karboxyl, commonly referred to as the carboxyl group, is a functional group in organic chemistry with the formula -COOH. It consists of a carbonyl carbon (C=O) attached to a hydroxyl group (–OH) on the same carbon. The group is a defining feature of carboxylic acids and participates in characteristic reactions that transform it into various derivatives.

Structure and properties: The carboxyl group comprises a carbonyl moiety and a hydroxyl group on the same carbon, leading to two resonance structures that distribute electron density between the two oxygens. This resonance stabilizes the conjugate base formed after deprotonation, giving carboxylates (–COO−). In aqueous solutions, carboxyl groups are moderately acidic, with typical pKa values around 4–5 for simple aliphatic carboxylic acids. The group is highly polar and capable of hydrogen bonding, which influences solubility and boiling points of compounds containing it.

Reactivity and derivatives: The carboxyl group is a versatile site for chemical transformations. It readily undergoes esterification with alcohols under acid catalysis to give esters and water. It also reacts with amines to form amides, a key reaction in peptide synthesis. Reduction of carboxylic acids yields primary alcohols, typically using strong reducing agents. Condensation between two carboxyl groups can produce anhydrides, while heating or catalytic conditions can lead to decarboxylation, releasing CO2. Carboxyl groups can be converted into other derivatives such as acyl chlorides, anhydrides, or esters depending on the reagents used.

Occurrence and significance: carboxyl groups are widespread in chemistry and biology. They are present in formic, acetic, and benzoic acids, as well as in amino acids, fatty acids, and many metabolic intermediates. At physiological pH, many carboxyl groups exist as carboxylate anions, contributing to the charge and reactivity of biomolecules.

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