Carboxylic acids represent a fundamental class of organic compounds characterized by the presence of a carboxyl group (-COOH). These compounds play crucial roles in biological systems and industrial processes, from amino acids to fatty acids.
Structure and Nomenclature
The carboxyl group consists of a carbonyl group (C=O) directly bonded to a hydroxyl group (-OH). The carbon atom in the carboxyl group is sp² hybridized, creating a planar geometry around the carbon atom.
Naming Conventions
Suffix: -oic acid
Prefix: Carboxyl-
Priority: Highest among common organic functional groups (higher than aldehydes, ketones, alcohols)
Properties of Carboxylic Acids
Acid Strength and Dissociation
Carboxylic acids are weak acids that dissociate in water according to the equilibrium:
RCOOH(aq)+H2O(l)⇌RCOO(aq)−+H3O(aq)+
The acidic nature arises from two key factors:
Polarization of the O-H bond
Resonance stabilization of the carboxylate ion
Factors Affecting Acid Strength
Halogenation: Increases acid strength by enhancing O-H bond polarization
Chain Length: Longer chains decrease acid strength due to electron-donating effects
pKa Values:
CH3COOH:pKa=4.76CF3COOH:pKa=0.23
Physical Properties
Boiling and Melting Points
Carboxylic acids exhibit higher boiling points compared to similar molecular weight alcohols due to:
Formation of dimers through hydrogen bonding
Strong intermolecular forces
The unique dimer formation involves two hydrogen bonds between two carboxylic acid molecules: