Carboxyl Group

Structure and Properties

The carboxyl group is a common functional group found in many biological molecules, especially in organic acids such as amino acids and fatty acids. It consists of a carbon atom double-bonded to an oxygen atom and single-bonded to a hydroxyl group (–COOH).

• Structure: The carboxyl group has the formula –COOH, where the carbon is attached to both a hydroxyl group (–OH) and a carbonyl group (C=O).

• Polarity: The group is highly polar due to the electronegative oxygen atoms, making molecules containing carboxyl groups hydrophilic (water-soluble).

• Acidity: Carboxyl groups can donate a proton (H+) from the –OH, making them acidic. This property is important in biological systems for maintaining pH balance.

Biological Significance

• Amino Acids: All amino acids contain a carboxyl group, which participates in peptide bond formation during protein synthesis.

• Fatty Acids: Fatty acids are long hydrocarbon chains ending with a carboxyl group, which is essential for their function in cell membranes and energy storage.

• Metabolic Reactions: Carboxyl groups are involved in key metabolic pathways, such as the citric acid cycle.

Ionization and Chemical Behavior

• Ionization: In aqueous solutions, the carboxyl group can lose a proton, forming a carboxylate ion (–COO−).

• Equation for Ionization:

• Reactivity: The carboxyl group can participate in condensation reactions, such as the formation of esters and amides.

Examples

• Acetic Acid: The main component of vinegar, with the formula CH3COOH.

• Citric Acid: Found in citrus fruits, contains three carboxyl groups.

Additional info: The wavy line in the image represents a bond to the rest of the molecule, indicating that the carboxyl group can be attached to various carbon skeletons in different biomolecules.