Resonance
Which of the following species is most stabilized by resonance?
Select the correct option:
Solution
CH2=CH–CH2+(allylcarbocation)
Resonance stabilization requires an empty orbital, lone pair, or radical center conjugated with an adjacent π bond, allowing electron delocalization. The allyl carbocation (CH₂=CH–CH₂⁺) is resonance-stabilized by two equivalent contributing structures: CH₂=CH–CH₂⁺ ↔ ⁺CH₂–CH=CH₂. The positive charge is delocalized over both terminal carbons, significantly lowering the energy. The ethyl carbocation (CH₃CH₂⁺) has no adjacent π system for resonance. The ethyl carbanion has no adjacent π system. The n-propyl radical lacks conjugation with a pi bond. Hence, the allyl carbocation is most stabilized by resonance.
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About This Question
- Subject
- chemistry
- Chapter
- some basic principles of organic chemistry
- Topic
- resonance
- Difficulty
- Medium
- Year
- 2025
Solution
Correct Answer:
CH2=CH–CH2+(allylcarbocation)
Resonance stabilization requires an empty orbital, lone pair, or radical center conjugated with an adjacent π bond, allowing electron delocalization. The allyl carbocation (CH₂=CH–CH₂⁺) is resonance-stabilized by two equivalent contributing structures: CH₂=CH–CH₂⁺ ↔ ⁺CH₂–CH=CH₂. The positive charge is delocalized over both terminal carbons, significantly lowering the energy. The ethyl carbocation (CH₃CH₂⁺) has no adjacent π system for resonance. The ethyl carbanion has no adjacent π system. The n-propyl radical lacks conjugation with a pi bond. Hence, the allyl carbocation is most stabilized by resonance.
This medium difficulty chemistry question is from the chapter some basic principles of organic chemistry, covering the topic of resonance. It appeared in the 2025 exam.
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