2018 O Level Chem P1 Q38 — Organic Chemistry / Addition Reactions Solution

Answer: C (2 and 3). The question asks which preparations convert a C=C double bond into a C-C single bond.

1) Making an ester from an alcohol and a carboxylic acid is a condensation reaction with no C=C bond involved. 2) Ethanol from ethene, \(\text{C}_2\text{H}_4 + \text{H}_2\text{O} \rightarrow \text{C}_2\text{H}_5\text{OH}\), adds across the C=C bond, turning it into a single bond. 3) Making margarine from a vegetable oil is catalytic hydrogenation, in which hydrogen adds across the C=C bonds, turning them into single bonds.

So preparations 2 and 3 convert C=C to C-C. Answer C.