Amines, Amides, and Imines: A Complete Guide 

Amines, amides, and imines are three fundamental classes of organic compounds containing nitrogen. While they all include nitrogen, their distinct bonding arrangements and electronic properties give them unique chemical behaviors. Understanding these differences is crucial for JEE-level organic chemistry.

1.0What are Amines?

Amines are organic derivatives of ammonia ($N{H}_3$). In an amine, one or more hydrogen atoms of ammonia are replaced by alkyl or aryl groups. The functional group is the amino group ( $-N{H}_2$,−NHR, or $-N{R}_2)$. Amines are characterized by the presence of a nitrogen atom with a lone pair of electrons, making them basic and nucleophilic.

Classification and Structure of Amines

Amines are classified based on the number of alkyl or aryl groups attached to the nitrogen atom.

• Primary (1o) Amine: The nitrogen atom is bonded to one carbon atom. Example: $C{H}_{3}C{H}_{2}N{H}_2$
• Secondary (2o) Amine: The nitrogen atom is bonded to two carbon atoms. Example: $C{H}_{3}NHC{H}_3$ (N-Methylethanamine).
• Tertiary (3o) Amine: The nitrogen atom is bonded to three carbon atoms. Example: (CH3​)_3​N (N,N-Dimethylethanamine).

The nitrogen atom in an amine is $s{p}^3$ hybridized, giving it a trigonal pyramidal geometry.

Properties of Amines

• Basicity: Amines are Brønsted-Lowry bases due to the lone pair on the nitrogen atom, which can accept a proton. Their basicity depends on the electron-donating effect of the alkyl groups. Generally, the order of basicity in the gas phase is 3^o>2^o>1^o>NH₃​. In aqueous solution, the basicity order is often 2^o>1^o>3^o>NH₃​ due to the combined effects of induction, steric hindrance, and solvation.
• Boiling Point: Primary and secondary amines can form intermolecular hydrogen bonds, leading to higher boiling points than hydrocarbons of similar molar mass. Tertiary amines cannot form hydrogen bonds with each other and have lower boiling points.

2.0What are Amides?

Amides are organic compounds that contain a carbonyl group (>C=O) bonded to a nitrogen atom. The functional group is the amide group (−CONH₂​, −CONHR, or −CONR₂​). Amides are considered derivatives of carboxylic acids.

Classification and Structure of Amides

Similar to amines, amides are classified as primary, secondary, or tertiary based on the number of non-hydrogen substituents on the nitrogen atom.

• Primary Amide: R−CONH₂​
• Secondary Amide: R−CONHR′
• Tertiary Amide: R−CONR′R′′

The amide group is a planar structure due to resonance. The lone pair on the nitrogen atom is delocalized into the carbonyl group, giving the C-N bond partial double-bond character. This resonance makes amides exceptionally stable.

Properties of Amides

• Basicity: Amides are very weak bases compared to amines. The resonance effect delocalizes the lone pair on the nitrogen, making it unavailable for protonation.
• Boiling Point: Primary and secondary amides have very high boiling points due to strong intermolecular hydrogen bonding. Tertiary amides have lower boiling points because they cannot form hydrogen bonds.

3.0What are Imines?

An imine (also known as a Schiff base) is an organic compound containing a carbon-nitrogen double bond (>C=N−R). The nitrogen atom is bonded to a hydrogen or an organic group, and the carbon atom is part of a carbonyl group in the reactant.

Structure and Formation of Imines

• Structure: The nitrogen atom in an imine is $s{p}^2$ hybridized. The geometry around the nitrogen and carbon atoms is trigonal planar.
• Formation: Imines are typically formed by the condensation reaction of an aldehyde or a ketone with a primary amine. A water molecule is eliminated in this reaction.$R-CHO+R^{\prime }-N{H}_{2}H+R-CH=N-R^{\prime }+H_{2}O$
  Imines are generally less stable than their corresponding amines and amides.

4.0Comparison of Amines, Amides, and Imines