JEE Chemistry 2025 Question with Solution

Given: Three molecules P, Q, and R are to be arranged in decreasing order of basicity.

Find: The correct order of basicity.

Basicity depends on the availability of the nitrogen lone pair for donation. More available lone pair means stronger basicity.

In P, the nitrogen is adjacent to a carbonyl group, so its lone pair is delocalized by resonance with the carbonyl group. This reduces its availability and hence decreases basicity.

In Q, the nitrogen is also associated with a carbonyl-containing conjugated system. Although the structure differs from P, the lone pair is still less available than in R because of conjugative effects.

In R, the nitrogen lone pair is most available for protonation because it is least involved in resonance or conjugation compared with P and Q.

Therefore, the decreasing order of basicity is $R > Q > P$.

The correct option is D.