NEET 2020 Chemistry Question 95 Solution

Under photochemical conditions (light/heat), toluene undergoes free radical substitution at the benzylic methyl group rather than electrophilic ring chlorination: $$\text{C}_6\text{H}_5\text{-CH}_3 + 2\text{Cl}_2 \xrightarrow{h\nu} \text{C}_6\text{H}_5\text{-CHCl}_2 + 2\text{HCl}$$ The compound formed is benzal chloride (benzylidene chloride, $$X$$).

Nucleophilic substitution of the two geminal chlorine atoms by water at 373 K yields an unstable gem-diol intermediate: $$\text{C}_6\text{H}_5\text{-CHCl}_2 + 2\text{H}_2\text{O} \xrightarrow{373\text{ K}} [\text{C}_6\text{H}_5\text{-CH(OH)}_2] + 2\text{HCl}$$

Geminal diols attached to the same carbon are thermodynamically unstable and spontaneously undergo elimination of a water molecule: $$[\text{C}_6\text{H}_5\text{-CH(OH)}_2] \xrightarrow{-\text{H}_2\text{O}} \text{C}_6\text{H}_5\text{-CHO (Benzaldehyde)}$$

Option (1) is Benzotrichloride ($$C_6H_5-CCl_3$$, which would give Benzoic acid upon hydrolysis); Option (2) is Benzyl chloride ($$C_6H_5-CH_2Cl$$, which yields Benzyl alcohol); Option (3) is Benzal chloride ($$C_6H_5-CHCl_2$$). Hence, X is Option (3).