JEE Chemistry 2024 Question with Solution

Given: Four structures are compared for Brønsted basic strength.

Find: Which structure is the strongest Brønsted base.

A Brønsted base is a species that accepts a proton, $\text{H}^+$. The stronger base is the one whose lone pair is more readily available for protonation.

From the solution text:

• Structure 1 is an aromatic amine, and the lone pair on nitrogen is involved in conjugation with the benzene ring, so it is less available.
• Structure 2 has even greater resonance delocalization of the nitrogen lone pair through aromatic rings, so it is also weakly basic.
• Structure 3 is more basic than the aromatic amines, but not as basic as a simple aliphatic amine.
• Structure 4 is a simple cyclic amine with an $sp^3$-hybridized nitrogen. Its lone pair is localized and readily available for protonation.

Therefore, Structure 4 has the greatest tendency to accept a proton.

The correct option is D.

Given: The options represent different nitrogen-containing structures.

Find: The structure with maximum proton-accepting tendency.

Basicity depends mainly on how available the lone pair on nitrogen is.

• In aromatic amines, the lone pair can participate in resonance with the aromatic ring. This delocalization decreases its availability for bonding with $\text{H}^+$.
• In a secondary aromatic amine attached to two phenyl rings, delocalization is even more significant, so the basicity decreases further.
• A simple amine without such resonance has a more available lone pair and is therefore more basic.
• A cyclic aliphatic amine with $sp^3$ nitrogen has a localized lone pair and higher electron density on nitrogen, making protonation easier.

Hence the strongest Brønsted base among the given options is Structure 4, so the correct option is D.

Note: The actual structural diagrams are not present in the provided input, so the reasoning is taken directly from the provided solution text.