Which test is used to detect a carbon-carbon double bond in organic compounds?

• A. Add bromine water
• B. Add acidified potassium permanganate
• C. Heat with sodium hydroxide
• D. Add litmus solution

Answer: (A)

Detecting a carbon-carbon double bond is most simply done by adding bromine water. The double bond acts as a site for electrophilic addition, so bromine adds across the bond to form a vic-dibromide. This reaction removes the orange-brown color of bromine water, turning it colorless, which is a clear visual signal that unsaturation is present. Alkanes don’t react with bromine water, so the solution stays colored, making this a straightforward test for C=C bonds.

Acidified potassium permanganate can also react with double bonds, but the result is oxidation with possible formation of diols or further oxidation products, and the color change can be less immediate or specific. Heating with sodium hydroxide isn’t a test for unsaturation at all, and litmus solution only indicates acidity or basicity, not the presence of carbon–carbon double bonds.