Q.83 Chemistry ⭐ 360° Option Elimination Active

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NEET 2026 Chemistry Question 83 Solution

Topic: Organic Chemistry: Some Basic Principles and Techniques · Official NTA Booklet Code 50

Question

Among the following, the compound having conjugated double bonds is

✓

Verified Against NTA Final Answer Key

Option (1) : hepta-1,3-diene

📚 Organic Chemistry: Some Basic Principles and Techniques Easy

📋 Given Parameters & Problem Setup

Requirement The compound having conjugated double bonds

Options hepta-1,3-diene, hepta-1,4-diene, hepta-1,5-diene, hepta-1,6-diene

⚡

The 30-Second Exam Hall Shortcut: ⚡ Conjugated Double Bond Rule (1,3-relationship)

⏱️ Save ~40 seconds

Alternate double and single bonds (-C=C-C=C-) mean locants differ by 2 (1,3-diene)!

1 Conjugated dienes require two double bonds separated by exactly ONE single bond.

2 In hepta-1,3-diene: C₁=C₂ - C₃=C₄ - C₅ - C₆ - C₇. Double bonds at positions 1 and 3 are separated by a single C₂-C₃ bond -> CONJUGATED!

3 In 1,4-diene: separated by two single bonds (isolated).

4 In 1,5-diene and 1,6-diene: separated by three and four single bonds (isolated).

5 Option (1) is instantly deduced in 5 seconds flat!

🛡️

Why You Can 100% Trust This Shortcut: IUPAC and fundamental organic chemistry definition: A conjugated system has overlapping p-orbitals across alternating single and double bonds.

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Step-by-Step Rigorous Workflow & Mathematical Proof

Step 1

Define Conjugated, Isolated, and Cumulated Dienes

1. Conjugated Dienes: Double bonds are separated by exactly one single bond (-C=C-C=C-). Continuous unhybridized p-orbitals allow π-electron delocalization. 2. Isolated Dienes: Double bonds are separated by two or more sp³ hybridized carbon atoms / single bonds (-C=C-(CH₂)ₙ-C=C-). 3. Cumulated Dienes (Allenes): Double bonds are adjacent to the same carbon atom (-C=C=C-).

\text{Conjugated system} \equiv -\text{C}=\text{C}-\text{C}=\text{C}-

• Delocalization stabilizes the system.

Step 2

Draw and Analyze the Structure of hepta-1,3-diene

Writing the IUPAC structure of hepta-1,3-diene: CH₂=CH-CH=CH-CH₂-CH₂-CH₃

\text{C}_1=\text{C}_2-\text{C}_3=\text{C}_4-\text{C}_5-\text{C}_6-\text{C}_7

• The first double bond is between C1 and C2.
• The second double bond is between C3 and C4.
• They are separated by a single σ bond between C2 and C3.
• Thus, hepta-1,3-diene contains conjugated double bonds.

Step 3

Analyze the Other Compounds

1. hepta-1,4-diene: CH₂=CH-CH₂-CH=CH-CH₂-CH₃ (separated by one -CH₂- group; isolated). 2. hepta-1,5-diene: CH₂=CH-CH₂-CH₂-CH=CH-CH₃ (separated by two -CH₂- groups; isolated). 3. hepta-1,6-diene: CH₂=CH-CH₂-CH₂-CH₂-CH=CH₂ (separated by three -CH₂- groups; isolated).

\text{Only hepta-1,3-diene is conjugated (Option 1)}

• Matches Option (1).

⭐

360° Option Elimination Engine Key Feature

Diagnose every choice: Know exactly why the right option works and why distractors fail.

4-Option Deep Scan

1 A

✓ 100% Correct

Verdict & Scientific Reason:

Exact match with the definition of a conjugated diene (alternating double and single bonds).

💡

Why this is airtight: None; elementary organic principle.

2 B

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. An isolated diene with an intervening sp³ methylene bridge.

⚠️

Student Fallacy (Why candidates pick this trap): Thinking a single methylene group allows conjugation.

3 C

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Isolated diene with two intervening methylene groups.

⚠️

Student Fallacy (Why candidates pick this trap): Misunderstanding the term conjugated.

4 D

✗ Incorrect

Verdict & Scientific Reason:

Incorrect. Terminal isolated diene with three intervening methylene groups.

⚠️

Student Fallacy (Why candidates pick this trap): Confusing terminal double bonds with conjugated double bonds.

⚠️

NTA Trap Alert: Confusing Cumulated, Conjugated, and Isolated Dienes

Students occasionally mix up conjugated (1,3-diene) with isolated (1,4-diene). Conjugation REQUIRES p-orbital overlap across adjacent carbons without an intervening sp³ spacer.

🛡️ How to avoid the -1 mark: Locants 1,3 = Conjugated; Locants 1,2 = Cumulated; Locants 1,4 or greater = Isolated.

📖

Core NEET Syllabus Standard

NEET Chemistry Core Syllabus · General Organic Chemistry Standard Benchmark

Core Scientific Principle Tested:

"A conjugated system consists of alternating single and multiple bonds."

Syllabus Focus: Classification of hydrocarbons, resonance, and conjugated systems

✓ Core NEET UG Syllabus Anchor Syllabus & Academic Standards ↗

1 and 3 are side-by-side conjugated glee; 1 and 4 are isolated at sea!

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NEET 2026 Chemistry Question 83 Solution

Question

The 30-Second Exam Hall Shortcut: ⚡ Conjugated Double Bond Rule (1,3-relationship)

Step-by-Step Rigorous Workflow & Mathematical Proof

Define Conjugated, Isolated, and Cumulated Dienes

Draw and Analyze the Structure of hepta-1,3-diene

Analyze the Other Compounds

360° Option Elimination Engine Key Feature

NTA Trap Alert: Confusing Cumulated, Conjugated, and Isolated Dienes

Core NEET Syllabus Standard

Ready to attempt under real exam pressure?

🔗 Related Questions — Organic Chemistry: Some Basic Principles and Techniques

Matching Organic Mixtures with Specific Distillation Techniques

Distinction Between Lassaigne’s Sodium Fusion Test and Copper Oxide Test for Carbon

Purification of Solids by Sublimation

Stability Order of Alkyl Carbocations (Hyperconjugation and Inductive Effect)

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