Question

An unknown alkyl halide $\left( A \right)$ reacts with an alcoholic KOH to produce a hydrocarbon ${C_3}{H_8}$ . Ozonolysis of the hydrocarbon forms $1$ mole of propionaldehyde and $1$ mole of formaldehyde. Suggest which of the following organic structures is the correct structure of the above alkyl halide $\left( A \right)$ .
a) $C{H_3}C{H_2}C{H_2}C{H_2}Br$
b) $C{H_3}CH\left( {Br} \right)CH\left( {Br} \right)C{H_3}$
c) $C{H_3}C{H_2}CH\left( {Br} \right)C{H_3}$
d) $BrC{H_2}C{H_2}C{H_2}Br$

Answer 1

The process takes place in two parts; first the dehydrohalogenation takes place and in the next process ozonolysis . Dehydrohalogenation is the removal of halogen and water molecules from alkane. Ozonolysis takes place when alkenes, alkynes or azo compounds are cleaved by ozone.
Complete answer:
-Products that are formed during ozonolysis are propionaldehyde and formaldehyde.
-The structure of propionaldehyde and formaldehyde is as follows:

-Ozonolysis takes place only when the unsaturated bond of alkenes, alkynes and azo compounds are cleaved by ozon.
-This denotes that there was a carbon-carbon double bond between propionaldehyde and formaldehyde.
-So the possible structure before ozonolysis are as follows:

-So from this structure we can say that the unknown alkyl halide $A$ may be $1 - bromobutane$ .
Now assuming $1 - bromobutane$ as the unknown alkyl halide we will carry out the reaction as follows:

-In this process, $HBr$ gets replaced by a double bond.
-The removal of halogen and $\beta -$ hydrogen from an alkane is the process of dehydrohalogenation.
-This $\beta -$ hydrogen is removed from $\beta -$ carbon atom which is adjacent to the halogen atom.
-Also during this process there is removal of water molecules.
-Later on when this $1 - butene$ undergoes ozonolysis it gives propionaldehyde and formaldehyde
-The reaction is given as follows:

-From all the above reaction we can say that the unknown alkyl halide $\left( A \right)$ is $C{H_3}C{H_2}C{H_2}C{H_2}Br$.

So the correct answer is option (a) $C{H_3}C{H_2}C{H_2}C{H_2}Br$

Note:
Ozonolysis of alkenes gives us aldehyde, ketones, alcohol or carboxylic acids.It is a type of redox reaction. It also helps to detect the location of double bond or triple bond present in alkenes and alkynes respectively.