Organic chemistry
Carboxylic acids, esters, amines, amides
Relate carboxylic acids, esters, amines and amides through functional-group structure, acid–base behaviour and condensation chemistry, including amide resonance.
IntuitionIntuition: carbonyl chemistry and nitrogen partners
A carboxylic acid contains an acidic –CO₂H group; replacing –OH by –OR creates an ester, while replacing it by a nitrogen group creates an amide. Amines contain nitrogen without the carbonyl activation found in amides, so their basicity and reactions follow a different balance.
SchoolSchool: formulas, names and interconversions
Definition: Functional-group definitions
A carboxylic acid has –CO₂H, an ester has –CO₂R, an amine is R–NH₂/R₂NH/R₃N, and an amide has –CON–. In an ester or amide, the acyl fragment comes from the acid; the oxygen or nitrogen substituent completes the family.
| Family | General pattern | Typical property |
|---|---|---|
| Carboxylic acid | –CO₂H | Weak acid; salt formation |
| Ester | –CO₂R | Often characteristic odour; hydrolysis |
| Amine | R–NH₂/R₂NH/R₃N | Basic nitrogen centre |
| Amide | –CON– | Resonance-stabilized bond |
Example: Esterification product
Solution
Ethyl ethanoate (ethyl acetate), CH₃COOCH₂CH₃, plus water. The reaction is reversible, so conditions that remove water or use an excess reagent can shift the equilibrium.
Amines are classified by the number of carbon groups attached to nitrogen: primary, secondary and tertiary. Basicity depends not only on alkyl substitution but also on solvation and protonation stability; a bulky tertiary amine is not automatically the most basic in water.
UndergraduateUniversity: acid–base strength and hydrolysis
Definition: Carboxylate stabilization
Deprotonation of a carboxylic acid produces a carboxylate ion in which negative charge is shared over two oxygens. Electron-withdrawing substituents further stabilize this anion and increase acidity; protonation reverses the equilibrium.
Example: Explain pKa order
Solution
The acetate ion delocalizes charge over two oxygens, whereas the ethoxide ion localizes most charge on one oxygen. Greater stabilization of the conjugate base makes acetic acid the stronger acid.
Ester hydrolysis is reversible under acid catalysis and essentially driven forward under base catalysis because the carboxylate product is deprotonated. The term “saponification” usually describes base-promoted hydrolysis of fats and oils into glycerol and carboxylate salts, not every possible ester cleavage.
AdvancedAdvanced: resonance, mechanism and polymers
Amide resonance places partial double-bond character on C–N and reduces rotation around that bond. This constraint is important in peptides and proteins, where planar peptide units support predictable folding. Acyl-transfer mechanisms explain why ester and amide formation can be catalyzed or activated rather than relying only on simple acid plus alcohol mixing.