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Chemistry Question 67 – NEET-UG 2025

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The correct order of decreasing basic strength of the given amines is :

The basic strength of an amine depends on the availability of the lone pair of electrons on the nitrogen atom for donation.

● Video Walkthrough
Step 1: Classify the Amines and Identify Key Factors✦ Active

Let's identify the type of each amine and the factors influencing its basicity:

1. **N-ethylethanamine** (CH3CH2)2NH): Secondary aliphatic amine. Two ethyl groups provide a strong +I effect, increasing electron density on nitrogen. Good solvation of its conjugate acid.

2. **Ethanamine** (CH3CH2NH2): Primary aliphatic amine. One ethyl group provides a +I effect, increasing electron density on nitrogen. Excellent solvation of its conjugate acid.

3. **N-methylaniline** (C6H5NHCH3): Secondary aromatic amine. The lone pair on nitrogen is delocalized into the benzene ring (resonance effect), decreasing basicity. The methyl group provides a slight +I effect.

4. **Benzenamine (Aniline)** (C6H5NH2): Primary aromatic amine. The lone pair on nitrogen is extensively delocalized into the benzene ring (resonance effect), making it the least basic.

💡 Teacher's Secret Hint

Remember that resonance stabilization of the lone pair on nitrogen in aromatic amines significantly reduces their basicity compared to aliphatic amines.

Step 2: Compare Basicity of Aliphatic vs. Aromatic Amines○ Expand

Aliphatic amines are significantly more basic than aromatic amines because the lone pair of electrons on nitrogen in aliphatic amines is localized and readily available for protonation, whereas in aromatic amines, it is delocalized into the benzene ring via resonance.

Therefore, N-ethylethanamine and ethanamine will be more basic than N-methylaniline and benzenamine.

💡 Teacher's Secret Hint

The resonance effect is a dominant factor in determining basicity, often outweighing inductive effects when comparing aromatic and aliphatic systems.

Step 3: Determine the Overall Order of Decreasing Basic Strength○ Expand

1. **Among aliphatic amines:** In aqueous solution, for ethyl groups, secondary amines are generally more basic than primary amines due to a better balance of +I effect and solvation. So, N-ethylethanamine > ethanamine.

2. **Among aromatic amines:** N-methylaniline is slightly more basic than benzenamine (aniline) because the methyl group provides a slight +I effect, making the lone pair slightly more available despite resonance. So, N-methylaniline > benzenamine.

Combining these, the overall order of decreasing basic strength is:

N-ethylethanamine > ethanamine > N-methylaniline > benzenamine.

This order matches option (3).

💡 Teacher's Secret Hint

Remember the general trend for basicity of amines in aqueous solution: Aliphatic secondary > Aliphatic primary > Aliphatic tertiary (for smaller alkyl groups) >> Aromatic amines.

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