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3.15: Conjugate Addition and Elimination in Aromatics

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    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.

    clipboard_ecfe98fc291e5068a44efe01a345481e6.png

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

    clipboard_ef9122f35750344af03e39dcedccff217.png

    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.

    clipboard_ee259f8b5228162023d318664d2579a15.png

    Answer

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    This page titled 3.15: Conjugate Addition and Elimination in Aromatics is shared under a CC BY-NC 3.0 license and was authored, remixed, and/or curated by Chris Schaller via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.