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JEE Main 2025 Apr 4 Shift 2, Chemistry Q1: Properties of Amines

JEE Main2025Apr 4, Shift 2Chemistry
Q.

The correct order of basicity for the following molecules is :

  1. A

    P > Q > R

  2. B

    R > P > Q

  3. C

    Q > P > R

  4. D

    R > Q > P

Solution

Basicity here depends on how much the N lone pair is tied up by conjugation with the adjacent C=O.

P is a normal planar amide — the lone pair is fully delocalised into C=O, so N is least basic.

Q has an extra ring C=C cross-conjugated with the C=O. Cross-conjugation is inefficient (the two -acceptors compete rather than reinforce), so the lone pair is less tied up than in P.

R is a bridgehead amide. By Bredt's rule, planar overlap of the N lone pair with C=O is geometrically forbidden, so the lone pair is fully localised on N — most basic.

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