Subtopic 1: Classification of Amines

Amines are classified by the number of carbon substituents on nitrogen: primary (1°, $RNH_{2}$), secondary (2°, $R_{2}NH$), and tertiary (3°, $R_{3}N$). They can also be aliphatic (R = alkyl) or aromatic (R = aryl). Aniline ($C_{6}H_{5}NH_{2}$) is the simplest and most important aromatic amine. Quaternary ammonium salts ($R_{4}N^{+}$) have four C-substituents and are permanently charged; they are not bases.

Subtopic 2: Preparation of Amines

Four main methods are tested in NEET:

• Nitro reduction: $RNO_{2}$ →(Sn/HCl) $RNH_{2}$. Direct and widely used; non-selective.
• Gabriel phthalimide synthesis: Selective for 1° aliphatic amines ONLY. ArX not compatible (no SN2). Cannot give 2° or 3° amines.
• Hoffmann bromamide degradation: $RCONH_{2}$ + $Br_{2}$/NaOH → $RNH_{2}$. Product has one fewer carbon. The carbonyl carbon is lost as $Na_{2}CO_{3}$.
• Ammonolysis of RX: RX + excess $NH_{3}$ → mixture of 1°/2°/3°/quaternary — poor selectivity.

Subtopic 3: Basicity of Amines

The most tested subtopic in NEET. Two separate situations must be memorised:

• Gas phase: 3° > 2° > 1° > $NH_{3}$ (more +I = more electron-rich N)
• Aqueous solution: 2° > 1° > 3° > $NH_{3}$ (solvation reverses 3°; $R_{3}NH^{+}$ poorly solvated)
• Aniline: Far weaker than all aliphatic amines; lone pair delocalized into ring by resonance.
• Substituent effects on aniline: EWG decreases basicity; EDG increases it slightly.

Subtopic 4: Identification Tests

Two key tests distinguish amine classes:

• Carbylamine test: $CHCl_{3}$ + 3KOH → RNC (foul isocyanide). ONLY 1° amines.
• Hinsberg test: $C_{6}H_{5}SO_{2}Cl$ + NaOH: 1° → soluble sulfonamide; 2° → insoluble sulfonamide; 3° → no reaction.

Subtopic 5: Diazonium Salts

Formed by diazotization: $ArNH_{2}$ + $NaNO_{2}$ + 2HCl at 0–5 °C → ArN_{2}^{+}$$Cl^{-}. Key reactions from diazonium salts:

Subtopic 6: Azo Dyes

Azo coupling produces –N=N– containing compounds (azo dyes). The medium controls which substrate couples: phenol needs alkaline medium (forms reactive phenoxide); aniline needs weakly acidic medium (keeps –$NH_{2}$ free and reactive). Azo dyes are the most important class of industrial synthetic dyes.