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Benzyne

  • Page ID
    38909
  • \( \newcommand{\vecs}[1]{\overset { \scriptstyle \rightharpoonup} {\mathbf{#1}} } \) \( \newcommand{\vecd}[1]{\overset{-\!-\!\rightharpoonup}{\vphantom{a}\smash {#1}}} \)\(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\) \(\newcommand{\id}{\mathrm{id}}\) \( \newcommand{\Span}{\mathrm{span}}\) \( \newcommand{\kernel}{\mathrm{null}\,}\) \( \newcommand{\range}{\mathrm{range}\,}\) \( \newcommand{\RealPart}{\mathrm{Re}}\) \( \newcommand{\ImaginaryPart}{\mathrm{Im}}\) \( \newcommand{\Argument}{\mathrm{Arg}}\) \( \newcommand{\norm}[1]{\| #1 \|}\) \( \newcommand{\inner}[2]{\langle #1, #2 \rangle}\) \( \newcommand{\Span}{\mathrm{span}}\)

    Hydrocarbon 1 is called benzyne.

    benzyne1.png

    Derivatives of 1 are called benzynes or arynes.

    eg:

    benzyne2.png

    If each triply bonded carbon atom in a benzyne molecule is sp-hybridized, as is typical of triply bonded carbon atoms, there would be severe angle strain in the molecule. It is more likely that each triply bonded carbon atom in a benzyne molecule is sp2-hybridized, in which case two sp2-hybridized orbitals that are not parallel to each other overlap laterally to form the pi bond that is not part of the loop of pi electrons (2).

    benzyne3.png

    In either case, the pi bond in a benzyne molecule that is not part of the loop of pi electrons would be very weak, which is consistent with the observation that, despite being aromatic, benzynes are extremely unstable and reactive. If generated in isolation, benzynes undergo rapid dimerization.

    eg:

    benzyne4.png

    Mechanism

    Step 1:

    benzyne5.png

    Step 2:

    benzyne6.png

    see also benzyne mechanism


    Benzyne is shared under a All Rights Reserved (used with permission) license and was authored, remixed, and/or curated by Gamini Gunawardena via source content that was edited to conform to the style and standards of the LibreTexts platform; a detailed edit history is available upon request.

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