Question

A hydrocarbon when treated with bromine water, the colour of bromine water gets decolourize, the given hydrocarbon can be:
A. 2- methyl butanol
B. 3,3- dimethyl-4-ethylhexane
C. 2- hydroxypropanoic acid
D. Propene

Answer 1

Hint: Bromine water is in red colour. When we are going to add bromine water to unsaturated compounds, then the red colour of the bromine water is going to be colourless. In this reaction bromine is going to add to the unsaturated compounds and forms respective bromo derivatives as the products.

Complete step by step solution:
-We have to find which substance contains unsaturation in its structure among the given options.
-Coming to give options, Option A, 2- methyl butanol.
-The structure of the 2- methyl butanol is as follows.

-In the above structure there is no unsaturation (Means no double or triple bonds), then 2- methyl butanol does not decolourize the bromine water to colourless.
-Coming to option B, 3,3- dimethyl-4-ethylhexane.
-The structure of 3,3- dimethyl-4-ethylhexane is as follows.

- In the above structure there is no unsaturation (Means no double or triple bonds), then 3,3- dimethyl-4-ethylhexane does not decolourize the bromine water to colourless.
-Coming to option C, 2- hydroxypropanoic acid.
- The structure of 2- hydroxypropanoic acid is as follows.

- In the above structure there is no unsaturation (Means no double or triple bonds), then 2- hydroxypropanoic acid does not decolourize the bromine water to colourless.
-Coming to option D, propene.
-The structure of propene is as follows.

-The reaction of propene with bromine water is as follows.

-Therefore, propene decoloursise the bromine water.

So, the correct option is D.

Note: Unsaturated hydrocarbons undergo addition reaction with bromine water, therefore the colour of the bromine water changes from a red colour to colourless. A saturated hydrocarbon does not contain double bonds therefore the colour of bromine water does not change.