Q.59 From the structures given below, identify the compounds
Group I (Structure)
Group II (Compound)
- 1. Ethylene
- 2. Indole butyric acid
- 3. Nicotine
- 4. Indole acetic acid
- 5. Gibberellic acid
- 6. Menthol
Identify Compounds from Organic Structures – Complete Explanation with Solution
In organic chemistry exams, students are often asked to identify compounds from their
skeletal or structural formulas. In this problem, four structures (P, Q, R, S) must be matched
with compounds like menthol, nicotine, indole butyric acid, and ethylene.
Let us solve each structure step-by-step using functional groups and structural clues.
Structure P → Menthol
Clues:
- Cyclohexane ring
- Alcohol group (–OH)
- Isopropyl and methyl substituents
A saturated cyclohexane ring bearing an –OH group with alkyl substituents is characteristic
of menthol, a monoterpene alcohol.
Therefore: P = Menthol (6)
Structure Q → Nicotine
Clues:
- Two nitrogen containing rings
- One pyridine ring (aromatic)
- One pyrrolidine ring
The presence of these two heterocyclic nitrogen rings clearly indicates the alkaloid
nicotine.
Therefore: Q = Nicotine (3)
Structure R → Indole Butyric Acid
Clues:
- Indole nucleus (benzene + pyrrole fused)
- Long side chain ending with –COOH
- Four-carbon chain (butyric acid)
An indole ring attached to a butyric acid side chain corresponds to
Indole Butyric Acid (IBA), a plant growth hormone.
Therefore: R = Indole butyric acid (2)
Structure S → Ethylene
Clues:
- CH2 = CH2
- Contains a double bond
- Simplest alkene
This is clearly ethylene (ethene), the simplest unsaturated hydrocarbon.
Therefore: S = Ethylene (1)
Final Matching Table
| Structure | Compound | Number |
|---|---|---|
| P | Menthol | 6 |
| Q | Nicotine | 3 |
| R | Indole Butyric Acid | 2 |
| S | Ethylene | 1 |
Correct Answer
(A) P-6, Q-3, R-2, S-1
Why Other Options Are Incorrect?
- Option B: Menthol is wrongly matched with gibberellic acid.
- Option C: Ethylene cannot be menthol.
- Option D: All structures mismatched.
Quick Exam Identification Tips
- Cyclohexane + –OH + isopropyl → Menthol
- Pyridine + pyrrolidine rings → Nicotine
- Indole + COOH side chain → Indole butyric acid
- CH2=CH2 → Ethylene
Conclusion:
By recognizing functional groups and ring systems, compounds can be identified quickly and accurately.
Practice such structure-based questions regularly for better exam performance.
