Classification Table
| Feature | 1° Amine | 2° Amine | 3° Amine | Quaternary Salt |
|---|---|---|---|---|
| Formula | ||||
| N–H bonds | 2 | 1 | 0 | 0 |
| Basicity (aq) | 2nd | 1st (strongest) | 3rd | Not a base |
| Gabriel? | Yes (aliphatic only) | No | No | No |
| Carbylamine? | Yes (foul smell) | No | No | No |
| Hinsberg (NaOH) | Soluble | Insoluble | No reaction | No reaction |
Diazonium Reaction Map
$ArN_{2}^{+}$$Cl^{-}$
├── + CuCl/HCl ────────────────→ ArCl [Sandmeyer]
├── + CuBr/HBr ────────────────→ ArBr [Sandmeyer]
├── + CuCN/KCN ────────────────→ ArCN [Sandmeyer]
├── + Cu°/HCl ─────────────────→ ArCl [Gattermann]
├── + $HBF_{4}$ →($\Delta$)─────────────→ ArF [Schiemann - ONLY ArF]
├── + $H_{3}PO_{2}$ ─────────────────→ ArH [Deamination]
├── + PhOH (alkaline) ────────→ orange-red azo dye
└── + $PhNH_{2}$ (weak acid)──────→ yellow azo dye
Basicity Trend (Aqueous)
| Compound | pKb (aq) | Relative Strength |
|---|---|---|
| ()_{2}NH (2°) | ≈ 3.27 | Strongest ↑ |
| CH_{3}$$NH_{2} (1°) | ≈ 3.38 | Strong |
| ()_{3}N (3°) | ≈ 4.19 | Moderate |
| ≈ 4.74 | Weak | |
| C_{6}H_{5}$$NH_{2} (aniline) | ≈ 9.38 | Weakest ↓ |
Aniline Resonance (SMILES: Nc1ccccc1)
The lone pair on N enters the ring → partial positive charge on N in resonance structures → N is less available for protonation → weak base.
N(+)–C=C–C=C–C=C (quinoid resonance form)
Preparation Decision Tree
Want a PRIMARY ALIPHATIC amine?
→ Use Gabriel phthalimide (clean, no mixtures)
→ Or Nitro reduction (if Ar$NH_{2}$ is acceptable)
→ Or Hoffmann bromamide (but product has –1C)
Want an AROMATIC AMINE (Ar$NH_{2}$)?
→ Use Nitro reduction ONLY (Gabriel won't work)
Want FEWER CARBONS in the product?
→ Use Hoffmann bromamide (–1C vs starting amide)