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Why does this molecule not exist

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    The bond angle in a normal pentagon is 108 degrees.
    Apparently this structure would cause too much strain and would thus break open.
    Why?
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    The ideal angle for C=C=C is 180 degrees, 108 degrees is a long way from that. You can bend bonds (an example would be cyclopropane) but bend them too much and they just break.
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    I think you can just about make 6-membered cyclic allenes (they're obviously incredibly reactive), but I don't think 5 is manageable.
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    (Original post by cpchem)
    I think you can just about make 6-membered cyclic allenes (they're obviously incredibly reactive), but I don't think 5 is manageable.
    Would make sense. If you can get benzyne then it would be logical that sp (ish) hybridisation is just about possible in a 6 membered ring.
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    (Original post by EierVonSatan)
    The ideal angle for C=C=C is 180 degrees, 108 degrees is a long way from that. You can bend bonds (an example would be cyclopropane) but bend them too much and they just break.
    And, of course - woo, triangles!

    /excitedcyclopropanechemist
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    (Original post by cpchem)
    And, of course - woo, triangles!

    /excitedcyclopropanechemist
    Ha, my masters sypervisor loves heterocylic strained rings. I was just looking up cyclic allenes/cumulenes since you mentioned it and yeah, 6 membered is the smallest I've found so far :teeth: It wouldn't surpise me if some physical chemist hasn't made something 'silly strained' for a few femtoseconds :mmm:
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    (Original post by EierVonSatan)
    Ha, my masters sypervisor loves heterocylic strained rings. I was just looking up cyclic allenes/cumulenes since you mentioned it and yeah, 6 membered is the smallest I've found so far :teeth: It wouldn't surpise me if some physical chemist hasn't made something 'silly strained' for a few femtoseconds :mmm:
    thanks for your help

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Updated: May 9, 2012
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