Quick Summary
Concept Tested: Basicity of Amines & Inductive Effect ( + I )
Chapter: Amines
Difficulty: ⭐⭐⭐
Time to Solve: 2 Minutes
Key Formula: $$Basicity \propto \text{Electron Density on Nitrogen}$$
Answer: Option B
Why: Alkyl groups are electron-donating (+I effect), increasing the electron density on the nitrogen atom, thereby making it more available to accept a proton.
The Question
Arrange the following amines in the order of increasing basic nature:
1. Ammonia ($\text{NH}_3$)
2. Methylamine ($\text{CH}_3\text{NH}_2$)
3. Dimethylamine ($( \text{CH}_3 )_2\text{NH}$)
Options:
(A) $( \text{CH}_3 )_2\text{NH} < \text{NH}_3 < \text{CH}_3\text{NH}_2$
(B) $\text{NH}_3 < \text{CH}_3\text{NH}_2 < ( \text{CH}_3 )_2\text{NH}$
(C) $\text{CH}_3\text{NH}_2 < ( \text{CH}_3 )_2\text{NH} < \text{NH}_3$
(D) $\text{CH}_3\text{NH}_2 < \text{NH}_3 < ( \text{CH}_3 )_2\text{NH}$
Quick Answer
The correct answer is Option B.
Basicity increases with the number of alkyl groups attached to the nitrogen atom. This is because alkyl groups are electron-donating groups ( + I effect ) which push electron density towards the nitrogen, increasing the availability of its lone pair for protonation.
Why Other Options Are Incorrect
Option A is incorrect: It places dimethylamine as the least basic, which is false. Dimethylamine has two alkyl groups donating electrons, making it more basic than ammonia and methylamine.
Option C is incorrect: It places ammonia as the most basic, which is false. Ammonia has no alkyl groups to donate electrons, so it is the least basic among the three.
Option D is incorrect: It places ammonia as more basic than methylamine, which is false. Methylamine has one electron-donating methyl group, increasing its basicity compared to ammonia.
Video Solution
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Understanding the Concept
The basicity of an amine is determined by the availability of the lone pair of electrons on the nitrogen atom to accept a proton ($H^+$).
Alkyl groups are known as electron-donating groups due to their Inductive Effect (+I Effect). When an alkyl group is attached to a nitrogen atom, it pushes electron density through the sigma bonds towards the nitrogen.
$$ \text{Electron Density on N} \uparrow \implies \text{Basicity} \uparrow $$
Therefore, as the number of alkyl groups attached to nitrogen increases, the basicity of the amine increases.
Detailed Step-by-Step Solution
Step 1: Identify the Formula and Number of Alkyl Groups
We analyze the structure of each amine to determine the number of alkyl groups attached to the nitrogen atom:
1. Ammonia ($\text{NH}_3$) has 0 alkyl groups attached to Nitrogen.
2. Methylamine ($\text{CH}_3\text{NH}_2$) has 1 alkyl group (the methyl group, $\text{CH}_3$) attached to Nitrogen.
3. Dimethylamine ($( \text{CH}_3 )_2\text{NH}$) has 2 alkyl groups attached to Nitrogen.
Step 2: Apply the +I Effect Principle
Alkyl groups are electron-releasing (+I effect). They push electron density towards the nitrogen atom.
As the number of alkyl groups increases:
- Nitrogen in Ammonia has the lowest electron density.
- Nitrogen in Methylamine has a higher electron density (due to one alkyl group).
- Nitrogen in Dimethylamine has the highest electron density (due to two alkyl groups).
Step 3: Compare Basicity Based on Electron Density
Basicity is directly proportional to the electron density on the nitrogen atom.
$$ \text{Electron Density} \propto \text{Basicity} $$
Thus, the order of basicity is determined by the number of alkyl groups:
$$ \text{NH}_3 < \text{CH}_3\text{NH}_2 < ( \text{CH}_3 )_2\text{NH} $$
This matches Option B.
Final Answer
✔ Option B is correct.
Essential Formulas for This Topic
1. Basicity Relation:
$$ Basicity \propto \text{Electron Density on Nitrogen Atom} $$
2. Inductive Effect ( +I ):
$$ \text{Alkyl groups push electrons towards the atom they are attached to.} $$
Common Mistakes to Avoid
Mistake 1: Confusing Basicity with Nucleophilicity
Wrong Thinking: “Methylamine is more nucleophilic than ammonia, so it is more basic.”
Correct Approach: While methylamine is more nucleophilic, the reason it is more basic is the +I effect increasing electron density on nitrogen, not just its reactivity. Basicity is a thermodynamic property (stability of the conjugate acid), whereas nucleophilicity is kinetic.
Mistake 2: Ignoring Steric Hindrance (Advanced Context)
Wrong Thinking: “Dimethylamine is more basic than Trimethylamine.” (This is a trap for larger groups where steric hindrance becomes significant).
Correct Approach: For small alkyl groups like methyl, basicity increases strictly with the number of alkyl groups. However, for very bulky groups (like t-butyl), steric hindrance can prevent protonation, reversing the trend.
Mistake 3: Assuming Solvation Effects Overrule Inductive Effect
Wrong Thinking: “Ammonia is smaller, so it is solvated better, making it more basic.”
Correct Approach: In gas phase, basicity increases strictly with alkyl groups. In solution, solvation stabilizes smaller ions more. However, the +I effect of alkyl groups is a strong driving force that usually dominates the basicity trend for simple amines like these.
Key Concept Summary
- Electron Donating: Alkyl groups are +I effect groups.
- Electron Density: More alkyl groups $\rightarrow$ higher electron density on Nitrogen.
- Lone Pair Availability: Higher electron density $\rightarrow$ lone pair is more available for protonation.
- Basicity Trend: Increases with the number of alkyl groups attached to Nitrogen.
Golden Rule: For simple aliphatic amines, Basicity Order is determined by the number of alkyl groups: $\text{RNH}_2 > \text{R}_2\text{NH} > \text{R}_3\text{N} > \text{NH}_3$.
Frequently Asked Questions
Q: Why is Ammonia the least basic among these?
A: Ammonia has no alkyl groups to donate electrons. The nitrogen atom has a lone pair, but it lacks the electron-donating push from alkyl groups that stabilizes the positive charge after accepting a proton.
Q: Does the size of the alkyl group matter?
A: For methyl, ethyl, and propyl groups, the basicity generally increases with the number of alkyl groups. However, for very bulky groups (like t-butyl), steric hindrance can reduce basicity.
Q: What is the +I effect?
A: The +I (Inductive) effect is the ability of an atom or group to push electron density through a sigma bond towards an adjacent atom. Alkyl groups are electron-releasing, so they exert a +I effect.
Q: Is basicity the same as acidity?
A: No. Basicity is the ability to accept a proton ($H^+$). Acidity is the ability to donate a proton ($H^+$). They are opposite properties.
Prerequisites to Solve This Question
- Understanding of the Inductive Effect (+I and -I).
- Knowledge of the structure and hybridization of Amines (sp3 hybridized).
- Concept of Basicity (proton acceptance) vs. Nucleophilicity.
After Solving This, You Can:
- ✔ Predict the basicity order of simple aliphatic amines.
- ✔ Understand the role of electron-donating groups in organic chemistry.
- ✔ Solve problems involving the basicity of aromatic vs. aliphatic amines.
Study Tips for This Topic
When studying amine basicity, always draw the structures. Visualizing the alkyl groups pushing electrons towards the nitrogen atom helps solidify the +I effect concept. Remember that in JEE exams, the trend for simple alkyl groups is strict: More Alkyl Groups = More Basicity.
Difficulty Rating & Exam Frequency
Difficulty: 3/5 Stars
JEE Main Frequency: High (Common in Organic Chemistry section).
JEE Advanced Frequency: Moderate.
Related Questions from Amines
Written by Nishant Kumar Gupta
Founder of Padho Likho JEE & Senior Chemistry Educator — 12+ Years Experience, Ex-Faculty Allen/Aakash/Narayana.
Last Updated: July 2026
Question Source: JEE Main 2003 PYQ
Topic: Amines