Question

How do you distinguish between chlorobenzene from benzyl chloride?
A.$AgN{O_3}$ test
B.Schiff reagent test
C.by analysis of elemental composition
D.by adding sodium bicarbonate

Answer 1

The major difference between chlorobenzene and benzyl chloride is the hybridization of the carbon atom with which the chlorine is attached. In chlorobenzene the hybridization is $s{p^2}$ whereas in benzyl chloride the hybridization is $s{p^3}$ of the carbon with which chlorine is attached.

Complete Step by step solution:
The major difference between chlorobenzene and benzyl chloride is the hybridization of the carbon atom to which the chlorine is attached. In case of chlorobenzene the hybridization is $s{p^2}$ which means the $C - Cl$ bond will have more $s$ character and hence the bond will be shorter. Also, chlorine has a lone pair of electrons on it, this lone pair undergoes delocalization in the benzene ring. Chlorine gives lone pairs through a partial$\pi$ bond and hence the bond order of $C - Cl$ bond increases and becomes more than one which makes the bond stronger. Stronger bonds are difficult to break and hence do not give any reaction with $AgN{O_3}$. Whereas in case of benzyl chloride the $C - Cl$ bond has $s{p^3}$ hybridization and is purely a single bond and hence it is easier to break this bond. Therefore, in the presence of $AgN{O_3}$ the benzyl chloride will react to give $AgCl$ precipitates which are white in color. And hence this test can be used to distinguish between chlorobenzene and benzyl chloride.

Note: Schiff’s reagent test is used to detect aldehydes, in the presence of aldehydes they give characteristic magenta color, so it is not used for above differentiation. Also elemental analysis will not help because that might show the detection of extra $C{H_2}$ group also of chlorine but cannot define where the chlorine will be attached. In the presence of sodium bicarbonate there will be no reaction in both the cases.