Free Radical Halogenation
Easychemistry
Major monochlorination product of propane under radical conditions (excess Cl2, light) is:
Select the correct option:
Solution
Incorrect! Answer:
2-Chloropropane
- Radical Formation: Under light (photolysis), Chlorine molecule cleaves into two Chlorine radicals (Cl⋅).
- Hydrogen Abstraction: The radicals can abstract a hydrogen from either a primary carbon (CH3) or a secondary carbon (CH2) of propane.
- Radical Stability: A secondary propyl radical (CH3−C˙H−CH3) is more stable than a primary propyl radical (CH3−CH2−C˙H2) due to greater hyperconjugation (6 versus 2 alpha H-atoms).
- Statics vs. Stability: Although there are 6 primary hydrogens and only 2 secondary hydrogens, the stability advantage of the secondary radical makes it the faster route.
- Major Product: The stable secondary radical then reacts with Cl2 to form 2-Chloropropane (Isopropyl chloride).
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About This Question
- Subject
- chemistry
- Chapter
- hydrocarbons
- Topic
- free radical halogenation
- Difficulty
- Easy
- Year
- 2025
Solution
Correct Answer:
2-Chloropropane
- Radical Formation: Under light (photolysis), Chlorine molecule cleaves into two Chlorine radicals (Cl⋅).
- Hydrogen Abstraction: The radicals can abstract a hydrogen from either a primary carbon (CH3) or a secondary carbon (CH2) of propane.
- Radical Stability: A secondary propyl radical (CH3−C˙H−CH3) is more stable than a primary propyl radical (CH3−CH2−C˙H2) due to greater hyperconjugation (6 versus 2 alpha H-atoms).
- Statics vs. Stability: Although there are 6 primary hydrogens and only 2 secondary hydrogens, the stability advantage of the secondary radical makes it the faster route.
- Major Product: The stable secondary radical then reacts with Cl2 to form 2-Chloropropane (Isopropyl chloride).
This easy difficulty chemistry question is from the chapter hydrocarbons, covering the topic of free radical halogenation. It appeared in the 2025 exam.
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