How will you convert: (i) 4-nitrotoluene to 4-methylbenzoic acid (ii) benzene to 3-chlorophenol (iii) propanoic acid to ethanamine (iv) 4-methylaniline to 3,5-dibromotoluene? Give one test to distinguish aniline from propan-1-amine.

1. 1 · Plan by counting carbons. (i) adds one carbon on the ring (CN). (iii) loses one carbon (Hoffmann). (ii) and (iv) change ring groups through the diazonium salt.
2. 2 · 4-Nitrotoluene to 4-methylbenzoic acid. Sn/HCl → 4-methylaniline → NaNO₂ + HCl, 273 to 278 K → CuCN/KCN (Sandmeyer) → 4-CH₃C₆H₄CN → H₃O⁺ → 4-CH₃C₆H₄COOH.
3. 3 · Benzene to 3-chlorophenol. HNO₃/H₂SO₄ → nitrobenzene → Cl₂/FeCl₃ → 3-chloronitrobenzene (-NO₂ is meta-directing) → Sn/HCl → diazotise → warm water.
4. 4 · Propanoic acid to ethanamine. NH₃, heat → CH₃CH₂CONH₂ → Br₂ + NaOH → CH₃CH₂NH₂.
5. 5 · 4-Methylaniline to 3,5-dibromotoluene. Br₂ water → 2,6-dibromo-4-methylaniline → NaNO₂ + HCl, 273 to 278 K → H₃PO₂ (hypophosphorous acid) → 3,5-dibromotoluene.
6. 6 · Distinguish aniline and propan-1-amine. Diazotise in the cold and add alkaline 2-naphthol: aniline gives an orange-red dye; propan-1-amine gives N₂ gas and no dye.
7. 7 · Close in one line. So Hoffmann, nitriles and diazonium salts together let you build almost any amine or aromatic compound.

Scoring tip: Write each step on its own arrow and give the temperature 273 to 278 K every time you diazotise.