Question

Benzene reacts with chlorine in sunlight to give a final product:
a) $CC{l_4}$
b) ${C_6}{H_6}C{l_6}$
c) ${C_6}C{l_6}$
d) ${C_6}{H_5}Cl$

Answer 1

To find the appropriate option for the given question, form the chemical equation from the question and solve it using a free radical mechanism. A free-radical reaction is a chemical reaction involving free radicals.

Complete answer:
Given, Benzene will react with chlorine in the presence of sunlight to give a final product.
Now, in the presence of ultraviolet light from the sunlight, without the presence of a catalyst, hot benzene will also undergo an additional reaction with chlorine. The ring delocalization is permanently broken, and a chlorine atom adds on to each carbon atom.
Thus, in the presence of sunlight, ${C_6}{H_6} + 3C{l_2} \to {C_6}{H_6}C{l_6}$
Therefore, in the presence of sunlight, benzene reacts with chlorine to form benzene hexachloride.

Hence, the required option for the given question is b) ${C_6}{H_6}C{l_6}$.

Additional Information: The reaction proceeds via free radical mechanism since the approaching reactive intermediate is free radical of chlorine $C{l^ - }$. Thus, by this mechanism, all the carbons of benzene will have equal share of electrons. Hence, the compound formed from this reaction is benzene hexachloride which is a gamma isomer, with other minor isomers.

Note: In the given reaction of benzene with chlorine in the presence of sunlight, catalysts like $AlC{l_3}$ are not used. Instead, direct $C{l_2}$ gas is used , in the presence of strong radiation of ultraviolet rays , which is then able to break open the double bonds of the benzene ring and facilitate the approach of the reactive intermediate of chlorine. Students need to keep the above information in mind before solving the sum to successfully solve it.