HOOC

HOOC is a shorthand notation used in organic chemistry to denote a carboxyl group, typically written as HOOC- when it serves as a substituent at the end of a carbon skeleton. In structural formulas, HOOC- indicates the presence of a carboxyl group (-COOH) attached to a molecule, for example in HOOC-CH2-COOH, which is malonic acid. The more common representations of the carboxyl group are -COOH or CO2H, but HOOC- is frequently encountered in condensed structural form.

The carboxyl group comprises a carbonyl carbon double-bonded to an oxygen and singly bonded to a hydroxyl group, giving the functional group the formula CO2H. In typical conditions, carboxyl groups are weakly acidic, with pKa values around 4 to 5, meaning they donate a proton to bases to form carboxylate anions (-COO−). In aqueous solution, many carboxyl-containing compounds exist as mixtures of their protonated (COOH) and deprotonated (COO−) forms depending on pH.

Carboxyl groups participate in a range of fundamental reactions. They undergo esterification with alcohols to form esters, often under acidic catalysis. They react with amines to form amides, usually via coupling agents. Decarboxylation can occur under heating or catalytic conditions, removing CO2. Carboxyl groups can be activated through derivative formation (acid chlorides, anhydrides) to facilitate further transformations.

In summary, HOOC is a common shorthand for the carboxyl functional group in chemical notation, central to the chemistry of carboxylic acids and their derivatives. In non-chemical contexts, HOOC may appear as an acronym, so interpretation depends on context.