Question

Give reasons for the following: (a) Chlorine is ortho/para directing in electrophilic aromatic substitution reactions, though chlorine is an electron withdrawing group.
(b) Racemic mixture is optically inactive.
(c) Allyl chloride is hydrolysed more readily than n-propyl chloride.

Hint:

- Chlorine is ortho/para directing because of the stabilization of the carbocation through resonance. - Racemic mixtures result in optical inactivity due to the equal amounts of enantiomers canceling each other’s rotation. - Allyl chloride is more readily hydrolyzed than n-propyl chloride due to the resonance stabilization of the allyl carbocation.

Answer 1

(a) Chlorine directs electrophilic aromatic substitution to ortho/para positions despite being an electron-withdrawing group.
Chlorine is ortho/para directing in electrophilic aromatic substitution reactions. Although chlorine withdraws electrons inductively, it donates electron density via resonance using its lone pairs. This resonance donation stabilizes the intermediate carbocation, with a greater stabilizing effect observed at the ortho and para positions relative to the chlorine atom.


(b) A racemic mixture is optically inactive.


Racemic mixtures are optically inactive. This is because a racemic mixture contains equal amounts of two enantiomers. Since enantiomers are non-superimposable mirror images, their optical rotations are equal and opposite, resulting in a net zero optical rotation.


(c) Allyl chloride undergoes hydrolysis more readily than n-propyl chloride.


Allyl chloride is hydrolyzed more readily than n-propyl chloride. The allyl carbocation formed during hydrolysis is stabilized by resonance with the adjacent double bond, which facilitates the reaction. Conversely, the n-propyl carbocation lacks this resonance stabilization, making it less stable and resulting in a slower hydrolysis rate.