Aryl Halides Reactivity
Hardchemistry
Chlorobenzene is less reactive than alkyl chloride in nucleophilic substitution because:
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Solution
Incorrect! Answer:
Aryl C–Cl bond strengthened by resonance & partial double bond character
- Resonance Effect: The lone pairs on the Chlorine atom in chlorobenzene are in conjugation with the π-electrons of the benzene ring.
- Bond Character: This conjugation gives the C−Cl bond a partial double bond character, making it shorter and much stronger than a typical C−Cl single bond in alkyl halides.
- Hybridization: The Carbon in chlorobenzene is sp2 hybridized (more electronegative), whereas in alkyl halides it is sp3. This holds the electrons tighter to the nucleus.
- Carbocation Instability: For SN1, the phenyl cation (C6H5+) would be very unstable due to lack of resonance stabilization.
- Steric/Electronic: The π-cloud of the benzene ring also tends to repel incoming nucleophiles.
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About This Question
- Subject
- chemistry
- Chapter
- halogen organics
- Topic
- aryl halides reactivity
- Difficulty
- Hard
- Year
- 2025
Solution
Correct Answer:
Aryl C–Cl bond strengthened by resonance & partial double bond character
- Resonance Effect: The lone pairs on the Chlorine atom in chlorobenzene are in conjugation with the π-electrons of the benzene ring.
- Bond Character: This conjugation gives the C−Cl bond a partial double bond character, making it shorter and much stronger than a typical C−Cl single bond in alkyl halides.
- Hybridization: The Carbon in chlorobenzene is sp2 hybridized (more electronegative), whereas in alkyl halides it is sp3. This holds the electrons tighter to the nucleus.
- Carbocation Instability: For SN1, the phenyl cation (C6H5+) would be very unstable due to lack of resonance stabilization.
- Steric/Electronic: The π-cloud of the benzene ring also tends to repel incoming nucleophiles.
This hard difficulty chemistry question is from the chapter halogen organics, covering the topic of aryl halides reactivity. It appeared in the 2025 exam.
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