How will you convert: (i) propan-1-ol to 3-hydroxy-2-methylpentanal (ii) ethanoic acid to ethanal (iii) benzene to 3-bromoacetophenone (iv) ethanoic acid to methane (v) propanoic acid to propenoic acid?

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Count the carbons for each. (i) 3 → 6: aldol. (ii) same carbons: only the group changes. (iii) ring plus 2 carbons. (iv) 2 → 1: decarboxylation. (v) same: add a C=C.
2 · Propan-1-ol to 3-hydroxy-2-methylpentanal. CH₃CH₂CH₂OH → (PCC) CH₃CH₂CHO → (dil. NaOH, aldol) CH₃CH₂CH(OH)CH(CH₃)CHO.
3 · Ethanoic acid to ethanal. CH₃COOH → (SOCl₂) CH₃COCl → (H₂, Pd-BaSO₄, Rosenmund) CH₃CHO.
4 · Benzene to 3-bromoacetophenone. C₆H₆ → (CH₃COCl, anhydrous AlCl₃, Friedel-Crafts) C₆H₅COCH₃ → (Br₂, FeBr₃) 3-bromoacetophenone, as -COCH₃ is meta-directing.
5 · Ethanoic acid to methane. CH₃COOH → (NaOH) CH₃COONa → (soda lime, heat) CH₄ + Na₂CO₃.
6 · Propanoic acid to propenoic acid. CH₃CH₂COOH → (Br₂, red phosphorus) CH₃CH(Br)COOH → (alcoholic KOH, heat; H₃O⁺) CH₂=CHCOOH.
7 · Close in one line. So each conversion is a chain of named steps, each with its reagent on the arrow.

Scoring tip: One arrow per step, with the reagent written on it and the intermediate named. A conversion with a missing reagent usually scores zero for that step.