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Part of OC-08 — Amines & Diazonium Salts

Exam Cheat Sheet — Amines & Diazonium Salts

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MUST-KNOW FACTS

Basicity Orders

Aqueous: 2° > 1° > 3° > $NH_{3}$ ≫ Aniline
Gas phase: 3° > 2° > 1° > $NH_{3}$ (reverse of aqueous 3° position)
Aniline pKb ≈ 9.38 (weak); methylamine pKb ≈ 3.38 (strong)

Preparation — Key Limitations

Gabriel → 1° aliphatic ONLY (no $ArNH_{2}$ , no 2°, no 3°)
Hoffmann → product has –1 carbon vs amide
Nitro reduction → all primary amines (no selectivity)

Distinction Tests

Test	Positive result	Class
Carbylamine ( $CHCl_{3}$ /KOH)	Foul smell (RNC)	1° ONLY
Hinsberg ( $PhSO_{2}Cl$ /NaOH)	Sulfonamide soluble	1°
Hinsberg	Sulfonamide insoluble	2°
Hinsberg	No reaction	3°

Diazonium Salt Reactions

Reagent	Product	Name
CuCl/HCl	ArCl	Sandmeyer
CuBr/HBr	ArBr	Sandmeyer
CuCN/KCN	ArCN	Sandmeyer
Cu°/HCl	ArCl	Gattermann
$HBF_{4}$ then $\Delta$	ArF	Schiemann (ONLY ArF route)
$H_{3}PO_{2}$	ArH	Deamination
PhOH (alkaline)	azo dye (orange-red)	Coupling
$PhNH_{2}$ (weak acid)	azo dye (yellow)	Coupling

Diazotization: $NaNO_{2}$ + 2HCl + $ArNH_{2}$ at 0–5 °C → $ArN_{2}^{+}$$Cl^{-}$

SMILES Quick Reference

Aniline: Nc1ccccc1
Benzenediazonium: [N+]#Nc1ccccc1.[Cl-]
Fluorobenzene: Fc1ccccc1
p-Hydroxyazobenzene: Oc1ccc(/N=N/c2ccccc2)cc1

Top NEET Traps

Aqueous 3° is WEAKER than 2° (solvation)
Gabriel cannot make aniline (no SN2 on ArX)
Hoffmann gives FEWER carbons (–1C)
Schiemann = ONLY ArF route
Phenol coupling = alkaline; aniline coupling = weakly acidic

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