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Q.
The reaction of toluene with $Cl_2$ in the presence of $FeCl_3$ gives '$X$' and reaction in presence of light gives '$Y$' Thus, '$X$' and '$Y$' are
AIPMTAIPMT 2010Hydrocarbons
Solution:
In presence of $FeCl _{3}$ and in dark, electrophilic substitution on the benzene ring by $Cl ^{+}$ion at ortho and para positions occurs to give o- and p- chlorotoluene.
Since methyl group activates the ring at ortho and para positions more than meta positions, the electroscopic substitution occurs mostly at these positions.
$C _{6} H _{5}- CH _{3}+ Cl _{2} \xrightarrow{ FeCl _{3}}\{ o$-chlorotoluene $\underset{(X)}{+ p}$-chlorotoluene $\}$
Hence, $X$ is o- and p- chlorotoluene.
On the other hand, if chlorine reacts with toluene in the absence of a catalyst but in the presence of UV light, substitution happens in the methyl group rather than the ring.
$C _{6} H _{5}- CH _{3}+ Cl _{2} \xrightarrow{\text { UV light }}\underset{(Y)}{C _{6} H _{5}- CCl _{3}}$
Hence, $Y$ is trichloromethylbenzene.