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🥼organic chemistry review

Benzyne Intermediate

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

Definition

A benzyne intermediate is a highly reactive, short-lived species that is involved in certain aromatic substitution reactions. It is a cyclic, unsaturated compound with a triple bond and a pair of adjacent carbon atoms that have lost their aromatic character.

Benzyne Intermediate cheat sheet for homework

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5 Must Know Facts For Your Next Test

  1. Benzyne intermediates are formed as a result of the removal of a halogen or other good leaving group from an aromatic ring, leaving behind a triple bond and a pair of adjacent carbon atoms.
  2. These intermediates are highly reactive and can undergo various reactions, such as nucleophilic addition, cycloaddition, and rearrangement reactions.
  3. Benzynes are commonly generated through the use of strong bases, such as n-butyllithium or lithium diisopropylamide (LDA), which abstract a halogen from an aromatic halide.
  4. The formation of benzyne intermediates is a key step in certain aromatic substitution reactions, such as the Kornblum-DeLaMare rearrangement and the Diels-Alder cycloaddition reaction.
  5. Benzynes are important intermediates in organic synthesis, as they allow for the introduction of various functional groups onto aromatic rings through subsequent reactions.

Review Questions

  • Explain how the formation of a benzyne intermediate is involved in aromatic substitution reactions.
    • The formation of a benzyne intermediate is a key step in certain aromatic substitution reactions, such as nucleophilic aromatic substitution (SNAr) and some electrophilic aromatic substitution (SEAr) reactions. In these reactions, a good leaving group (e.g., a halogen) is removed from the aromatic ring, leaving behind a triple bond and a pair of adjacent carbon atoms that have lost their aromatic character. This highly reactive benzyne intermediate can then undergo various reactions, such as nucleophilic addition or cycloaddition, to introduce new substituents onto the aromatic ring while maintaining its aromatic character.
  • Describe the conditions typically used to generate a benzyne intermediate and the subsequent reactions it can undergo.
    • Benzyne intermediates are commonly generated through the use of strong bases, such as n-butyllithium or lithium diisopropylamide (LDA), which abstract a halogen from an aromatic halide. This leaves behind the reactive benzyne species with a triple bond and a pair of adjacent carbon atoms. The benzyne intermediate can then undergo various reactions, including nucleophilic addition, cycloaddition, and rearrangement reactions. For example, in the Diels-Alder cycloaddition reaction, the benzyne can react with a diene to form a cyclohexene product, while in the Kornblum-DeLaMare rearrangement, the benzyne can undergo a sigmatropic rearrangement to form a different aromatic product.
  • Analyze the importance of benzyne intermediates in organic synthesis and their role in the development of new synthetic methodologies.
    • Benzyne intermediates are crucial in organic synthesis, as they provide a versatile platform for the introduction of various functional groups onto aromatic rings. The high reactivity of benzynes allows for the rapid construction of complex aromatic structures through subsequent reactions. The ability to generate and trap benzyne intermediates has led to the development of numerous synthetic methodologies, such as the Diels-Alder cycloaddition, the Kornblum-DeLaMare rearrangement, and other reactions that utilize the unique reactivity of these intermediates. The continued study and application of benzyne chemistry has been instrumental in the advancement of organic synthesis, enabling the efficient construction of complex aromatic compounds and expanding the toolbox of synthetic organic chemists.
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