Question

A hydrocarbon Y decolourises Bromine water. On ozonolysis it gives 3-methyl butanal and formaldehyde. Give the name and formula of the compound.

Answer 1

When a hydrocarbon decolourises Bromine water, they are likely to be the unsaturated ones i.e. alkenes and alkynes because the double or triple bonds break and those valences of carbon are fulfilled by Bromine. When the bromine reacts, it decolourises. This reaction is used as a confirmed test for the unsaturated compounds.

Complete step by step answer:
As Y decolourises bromine water, it is an unsaturated hydrocarbon and this hydrocarbon is alkane because bromide will undergo addition reactions with unsaturated compounds containing a double or a triple bond became and becomes very unstable hence bromine water is broken down to release Br- and H for substitution in the carbon - carbon chain. When bromine water is added to an unsaturated compound, the former gets added to the latter, hence turning colourless from its reddish-brown colour.
From the products of ozonolysis, we can predict the structure of this alkene.
We know that on ozonolysis, it gives 3-methyl butanal and formaldehyde. Now, we will see the reaction.
$C{H_3}CH(C{H_3})C{H_2}CH = C{H_2} + {O_3} \to C{H_3}CH(C{H_3})C{H_2}CH = 0 + HCH{O_2}$

Thus, the name of the compound is 4-methyl-1-pentene and its formula is $C{H_3}CH(C{H_3})C{H_2}CH = C{H_2}$

Note: Ozonolysis is the organic chemical reaction wherein the ozone $\left( {{O_3}} \right)$ is employed to cleave the unsaturated bonds of alkenes, alkynes, and azo compounds (compounds with the functional diazinyl functional group). Ozonolysis is an organic redox reaction. The oxidation of alkenes with the help of ozone will give alcohols, aldehydes, ketones, or carboxylic acids. And ozonolysis of alkynes gives acid anhydrides or diketones. If water is present in the reaction, the acid anhydride undergoes hydrolysis to yield two carboxylic acids.