Question

How many of the given compounds cannot decolourise bromine water

Answer 1

• We know that the reddish brown colour of bromine solution in carbon tetrachloride is discharged when bromine adds up to an unsaturation site.

• Cyclobutane (a) and cyclohexane (c) do not have any $\pi$ bonds for addition reactions. Hence, they will not decolourise bromine water.

• Compound (b) is benzene. Benzene has $\pi$ electrons that are delocalised over the entire ring. Benzene will not undergo addition reactions since addition reactions will destroy the aromaticity of benzene. Hence, it will not decolourise bromine water.

• An alkyne is given in option (d). Since unsaturation is present in but-2-yne, it will decolourise bromine water.

• Thus, the compounds given in (a), (b), and (c) will not decolourise bromine water.