The carboxyl group is a functional group with the chemical structure –COOH, consisting of a carbon double-bonded to an oxygen (C=O) and single-bonded to a hydroxyl group (–OH). It is commonly found in organic acids, such as amino acids and fatty acids, and plays a central role in biochemistry and metabolism.
Chemical Structure:
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R – C – OH
R = the rest of the molecule (carbon chain or atom group)
Known as the carboxylic acid group because it behaves like a weak acid
Key Properties:
Property
Description
Polarity
Highly polar due to electronegative oxygen atoms
Acidity
Weak acid; can donate a proton (H⁺) from the –OH group to become carboxylate (–COO⁻)
Solubility
Increases water solubility of molecules due to hydrogen bonding
Reactivity
Can form esters, amides, and undergo decarboxylation in metabolism
Biological Importance:
Role
Examples
Amino acids
Each amino acid has a carboxyl group (–COOH) and an amino group (–NH₂)
Fatty acids
Long hydrocarbon chains with a terminal carboxyl group
Metabolic reactions
Many biochemical pathways involve carboxylation and decarboxylation (adding or removing –COOH)
pH buffering
Helps stabilize biological pH by releasing or accepting H⁺ ions
Carboxyl vs. Carboxylate:
Form
Structure
Description
Carboxyl
–COOH
Protonated (acid form)
Carboxylate
–COO⁻
Deprotonated (conjugate base) at physiological pH (~7.4)
