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JEE Main 2026 Apr 2 Shift 1, Chemistry Q18: Properties of Alkyl Halides (Halo Alkanes) & Aryl Halides (Halo Arenes)

JEE Main2026Apr 2, Shift 1Chemistry
Q.

Consider the three aromatic molecules (P, Q and R) whose structures have been given below :

The correct order regarding the reactivity of these compounds with

under optimum but slightly acidic medium is :

  1. A

    P > Q > R

  2. B

    R > P > Q

  3. C

    R > Q > P

  4. D

    P > R > Q

Solution

Diazonium coupling is an electrophilic aromatic substitution that requires the nitrogen lone pair on the group to be in conjugation with the ring (so that the para position is highly activated).

In P (unhindered N,N-dimethylaniline) the group lies in the plane of the ring; full donation is possible, so coupling is fast.

In Q, a single ortho-methyl group sterically twists the slightly out of the plane, reducing resonance donation.

In R, two ortho-methyls force the dimethylamino group nearly perpendicular to the ring (steric inhibition of resonance), almost shutting off the effect.

Therefore reactivity follows P > Q > R.

Concept behind this question

Properties of Alkyl Halides (Halo Alkanes) & Aryl Halides (Halo Arenes)Notes, formulas and examples →

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