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🥼organic chemistry review

Allyl

Written by the Fiveable Content Team • Last updated September 2025
Written by the Fiveable Content Team • Last updated September 2025

Definition

The allyl group is a functional group in organic chemistry that consists of a vinyl group (a carbon-carbon double bond) with a methylene group (CH2) attached. It is an important structural feature in many organic compounds and plays a key role in the reactions of ethers, as discussed in the context of the topic 18.3 Reactions of Ethers: Acidic Cleavage.

5 Must Know Facts For Your Next Test

  1. The allyl group is susceptible to nucleophilic attack due to the presence of the carbon-carbon double bond.
  2. Allyl ethers can undergo acidic cleavage, where the ether bond is broken, and the allyl group is converted to an allyl cation.
  3. The allyl cation is a stabilized carbocation due to the resonance stabilization provided by the vinyl group.
  4. Allyl ethers are commonly used as intermediates in organic synthesis due to the reactivity of the allyl group.
  5. The acidic cleavage of allyl ethers can be used to selectively remove the allyl protecting group from alcohol and amine functional groups.

Review Questions

  • Explain the structural features of the allyl group and how they contribute to its reactivity.
    • The allyl group consists of a vinyl group (a carbon-carbon double bond) with a methylene group (CH2) attached. This structural arrangement allows for resonance stabilization of the allyl cation, which is formed during the acidic cleavage of allyl ethers. The presence of the carbon-carbon double bond also makes the allyl group susceptible to nucleophilic attack, contributing to its reactivity in organic reactions.
  • Describe the role of the allyl group in the acidic cleavage of ethers, and how this reaction can be used in organic synthesis.
    • During the acidic cleavage of allyl ethers, the ether bond is broken, and the allyl group is converted to a stabilized allyl cation. This allyl cation can then be attacked by a nucleophile, leading to the selective removal of the allyl protecting group from alcohol or amine functional groups. The ability to selectively cleave allyl ethers makes them valuable intermediates in organic synthesis, as the allyl group can be used to protect and then selectively deprotect these functional groups as needed during the synthetic process.
  • Analyze how the reactivity of the allyl group, specifically its susceptibility to nucleophilic attack and the stability of the allyl cation, influences its behavior in the context of the reactions of ethers.
    • The allyl group's reactivity, stemming from the presence of the carbon-carbon double bond and the ability to form a stabilized allyl cation, is a key factor in its behavior during the reactions of ethers. The susceptibility of the allyl group to nucleophilic attack allows for the selective cleavage of allyl ethers under acidic conditions, where the ether bond is broken, and the allyl group is converted to an allyl cation. The stability of this allyl cation, due to resonance stabilization, further facilitates the selective removal of the allyl protecting group, making it a valuable tool in organic synthesis.