Hydrocarbon Hyperconjugation Stability of Alkene Question JEE Main 2026

Quick Summary

Question Type: Alkene stability order and hyperconjugation comparison
Chapter: Hydrocarbon – Stability of Alkenes
Difficulty: ⭐⭐ Easy
Time to Solve: 2-3 minutes
Key Formula: More substituted alkene is generally more stable; trans > cis for the same degree of substitution
Correct Answer: (C) I > III > II > IV
Why: Alkene stability increases with substitution due to hyperconjugation. So tetra-substituted alkene I is most stable, then tri-substituted III, then trans-di-substituted II, and cis-di-substituted IV is least stable.

The Question

JEE Main 2026 (24 January Morning Shift) – Hydrocarbon

Arrange the following alkenes in decreasing order of stability.

Choose the correct answer from the options given below:

(A) III > I > II > IV
(B) III > II > I > IV
(C) I > III > II > IV
(D) I > III > IV > II

Quick Answer

Correct Option: (C) I > III > II > IV

Reasoning: Stability of alkenes depends mainly on:

• degree of substitution around the double bond
• hyperconjugation
• cis-trans effect for similarly substituted alkenes

So the order becomes:

• I = tetra-substituted alkene, most stable
• III = tri-substituted alkene
• II = trans-di-substituted alkene
• IV = cis-di-substituted alkene, least stable among these

Therefore, the decreasing order of stability is I > III > II > IV.

Video Solution

If you want the full explanation in a clear step-by-step teaching format, watch the video solution below:

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Understanding the Concept

Why More Substituted Alkenes Are More Stable

Alkenes become more stable when more alkyl groups are attached to the double-bonded carbons. This happens mainly because alkyl groups provide electron density through hyperconjugation and the +I effect.

Stability: tetra-substituted > tri-substituted > trans-di-substituted > cis-di-substituted

For alkenes with the same substitution level, the trans form is generally more stable than the cis form because steric repulsion is lower.

The Key Principle

1. First compare the degree of substitution of the double bond
2. Then compare cis and trans forms if substitution is similar
3. Higher hyperconjugation means higher alkene stability

Detailed Step-by-Step Solution

Step 1: Identify the Type of Each Alkene

• I is tetra-substituted
• III is tri-substituted
• II is trans-di-substituted
• IV is cis-di-substituted

Step 2: Apply Stability Rule

Download Handwritten Solution

• Tetra-substituted alkene has maximum hyperconjugation, so it is most stable
• Tri-substituted alkene is next in stability
• Between cis and trans disubstituted alkenes, trans is more stable than cis

Step 3: Compare II and IV Carefully

• Both II and IV are disubstituted alkenes
• II is trans, so steric repulsion is smaller
• IV is cis, so steric repulsion is larger
• Hence II is more stable than IV

Step 4: Write Final Order

• I > III > II > IV

So the correct option is (C).

Final Answer

Option (C): I > III > II > IV ✓

The correct decreasing order of alkene stability is I > III > II > IV.

Essential Formulas for This Topic

Primary Rules

1. Substitution Stability Rule:
   • tetra-substituted > tri-substituted > di-substituted > mono-substituted
   • More alkyl groups increase stability
   • Reason: hyperconjugation and +I effect
2. Cis-Trans Stability Rule:
   • trans alkene is more stable than cis alkene
   • Trans arrangement has less steric hindrance
   • This applies when degree of substitution is the same
3. Hyperconjugation Rule:
   • More alpha C-H bonds around the double bond increase stability
   • Greater hyperconjugation means greater alkene stability
   • Highly substituted alkenes show stronger stabilization

Important Constants

• Hyperconjugation stabilizes alkenes
• Alkyl groups donate electron density toward the double bond
• Trans alkenes usually have less steric strain than cis alkenes
• Substitution and stereochemistry both affect alkene stability

Common Mistakes to Avoid

❌ Mistake 1: Ignoring Degree of Substitution

Wrong Thinking: “Only cis/trans matters here.”

Correct Approach: First compare substitution. Tetra-substituted and tri-substituted alkenes are more stable than disubstituted ones.

❌ Mistake 2: Reversing Cis and Trans Stability

Wrong Approach: Taking cis alkene as more stable than trans alkene

Correct Approach: For similarly substituted alkenes, trans is generally more stable because it has lower steric repulsion.

❌ Mistake 3: Using Only Visual Size Without Concept

Common Error:

• Trying to guess from appearance only
• Not identifying whether the alkene is tetra-, tri-, or di-substituted

Correct Approach: Count the alkyl substituents attached to the double-bonded carbons first.

❌ Mistake 4: Forgetting Hyperconjugation

Wrong Thinking: “All substituted alkenes have almost same stability.”

Correct Understanding:

• More substituted alkenes have more hyperconjugative stabilization
• This strongly affects stability order
• That is why I and III are more stable than II and IV

Key Concept Summary

What You Must Remember

1. More substituted alkene is more stable: Due to hyperconjugation
2. Tetra-substituted is most stable: It has maximum alkyl substitution
3. Trans is more stable than cis: When substitution is same
4. Hyperconjugation is the main idea: It stabilizes the double bond
5. Always identify alkene type first: Then compare stereochemistry

The Golden Rule for Alkene Stability Questions

“First compare substitution, then compare cis/trans if needed.”

Frequently Asked Questions

Q1: Why is alkene I most stable?

A: Because it is tetra-substituted and has maximum hyperconjugative stabilization.

Q2: Why is alkene III more stable than II?

A: Because III is tri-substituted while II is only disubstituted.

Q3: Why is trans alkene II more stable than cis alkene IV?

A: Because trans arrangement reduces steric repulsion between substituents.

Q4: What is the role of hyperconjugation here?

A: Hyperconjugation donates electron density and stabilizes the double bond more in highly substituted alkenes.

Q5: What is the final decreasing order of stability?

A: I > III > II > IV.

Prerequisites to Solve This Question

Before attempting this problem, you should understand:

1. Alkene structure: Identifying substituents around a double bond
2. Hyperconjugation: Its role in stability
3. Inductive effect: Basic electron-donating effect of alkyl groups
4. Cis-trans isomerism: Stability difference between geometric isomers
5. Organic comparison logic: Ranking structures systematically

After Solving This, You Can:

✅ Compare stability of substituted alkenes confidently
✅ Use hyperconjugation in Hydrocarbon questions
✅ Distinguish cis and trans alkene stability
✅ Solve JEE Main alkene stability MCQs faster
✅ Avoid common substitution-counting mistakes
✅ Apply the same logic to other unsaturation stability problems

Study Tips for This Topic

For JEE Main:

1. Memorize the substitution order: tetra > tri > di > mono
2. Remember trans > cis: For same substitution level
3. Practice visual counting: Count alkyl groups around double bond quickly
4. Revise hyperconjugation examples: JEE often asks stability through this idea

Common JEE Variants:

• Arrange alkenes in order of stability
• Compare cis and trans alkene stability
• Hyperconjugation-based order questions
• Most stable or least stable alkene among given options

Difficulty Rating & Exam Frequency

Difficulty Level: ⭐⭐ (2/5) – Easy
JEE Main Frequency: High – Alkene stability questions are common in Hydrocarbon
JEE Advanced Frequency: Medium – Often combined with mechanistic or thermodynamic reasoning
Topic Importance: Very High – Hyperconjugation and stability are core concepts in organic chemistry

Written by Nishant Kumar
Chemistry Educator with 10+ Years of Experience Teaching JEE Aspirants
Founder – PadhoLikhoJEE

Last Updated: March 2026
Question Source: JEE Main 2026 PYQ
Topic: Hydrocarbon – Stability of Alkenes