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Chemistry LibreTexts

3.15: Conjugate Addition and Elimination in Aromatics

  • Page ID
    196982
  • In conjugate addition, a carbonyl group turns a neighbouring alkene into an electrophilic site. An enone, such as the one below, has two electrophilic positions.

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    A similar situation happens when pi-acceptors such as nitro groups are attached to aromatic rings.

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    The key step in the mechanism is the loss of the halide ion, which allows the aromaticity to be restored.

    clipboard_e857af681fb48fd4f4798a45a0d128492.png

    Exercise \(\PageIndex{1}\)

    The location of the halogen and the electron-withdrawing group matters. Explain why the reaction occurs if the groups are in the 1 and 2 positions (ortho to each other) or the 1 and 4 positions (para to each other), but not if they are in the 1 and 3 positions (meta to each other).

    clipboard_e064f94d068afc657903bb40413f7f9bb.png

    Exercise \(\PageIndex{2}\)

    Explain why the reaction is faster if additional electron-withdrawing groups are present.

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    Answer

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