2020 O Level Chem P1 Q39 — Organic Chemistry / Reaction Pathways Solution

Answer: A (addition, oxidation, esterification). Follow the flow chart from ethene. The first step, ethene to ethanol, is the addition of steam across the C=C double bond (hydration), so it is an addition reaction. The second step, ethanol to ethanoic acid, is brought about by an oxidising agent such as acidified potassium manganate(VII), so it is oxidation.

The third step, ethanoic acid reacting with ethanol to form an ester, ethyl ethanoate, is esterification: a carboxylic acid plus an alcohol gives an ester and water.

So the three reaction types, in order, are addition, oxidation and esterification, which is row A. Common error: calling the first step substitution — alkenes react by addition because of their double bond, not by substitution. The answer is A.