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JEE Main 2025 Jan 24 Shift 1, Chemistry Q19: Properties of Alkyl Halides (Halo Alkanes) & Aryl Halides (Halo Arenes)

JEE Main2025Jan 24, Shift 1Chemistry
Q.

Given below are two statements :

Statement-I : The conversion proceeds well in the less polar medium.

Statement-II : The conversion proceeds well in the more polar medium.

In the light of the above statements, choose the correct answer from the options given below.

  1. A

    Both statement I and statement II are true

  2. B

    Both statement I and statement II are false

  3. C

    Statement I is false but statement II is true

  4. D

    Statement I is true but statement II is false

Solution

Both reactions are bimolecular substitutions (S2) on a primary alkyl halide. Solvent effects on S2 depend on how the charge is distributed in going from reactants to the transition state.

Statement I (hydroxide reacts with butyl chloride):

Reactants carry a concentrated negative charge on HO. In the transition state, this charge is partially spread over the entering O, the central C, and the departing Cl, so the TS is less polar than the reactants. A polar protic solvent stabilises the reactants more than the TS and raises the activation energy. The reaction therefore proceeds better in a less polar medium. Statement I is correct.

Statement II (neutral amine RN reacts with butyl chloride):

Reactants are uncharged (low charge density). In the TS, partial positive charge develops on N and partial negative charge on the leaving Cl, so the TS is more polar than the reactants. A more polar solvent stabilises this charged TS, lowering . The reaction therefore proceeds better in a more polar medium. Statement II is correct.

Both statements are true. Option (1).

Concept behind this question

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

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