Isomerism In Hydrocarbons
How many structural isomers are possible for the molecular formula C₅H₁₂?
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About This Question
- Subject
- chemistry
- Chapter
- hydrocarbons
- Topic
- isomerism in hydrocarbons
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
3
C₅H₁₂ corresponds to pentane (degree of unsaturation = 0, so all alkanes). The three structural (constitutional) isomers are: (1) n-Pentane: CH₃–CH₂–CH₂–CH₂–CH₃ — straight-chain; (2) Isopentane (2-methylbutane): CH₃–CH(CH₃)–CH₂–CH₃ — one branch at C2; (3) Neopentane (2,2-dimethylpropane): C(CH₃)₄ — central carbon bearing four methyl groups. No additional isomers exist; any other arrangement either repeats one of these or violates valency. Sanity check: 4 carbons in main chain with 1 branch = isopentane; 3-carbon main chain with 2 methyls at C2 = neopentane. Total = 3.
This easy difficulty chemistry question is from the chapter hydrocarbons, covering the topic of isomerism in hydrocarbons. It appeared in the 2025 exam.
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