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A2 - Kekule's model / benzene

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    Can someone explain the part about carbon-carbon bond lengths in:
    Kekule's model
    Benzene

    And also can you explain the actual lengths of C-C and C=C bonds in regular compounds, like alkanes/alkenes.

    The book is a little :confused: on this part, for me atleast.

    Thanks a bunch!
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    The Carbon carbon bonds are half way between C-C and C=C in length. (are intermediate in length)

    Implying there is '1 and a half bonds' in benzene, hope that helps!
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    Oh okay, so in benzene the carbon to carbon bonds are all the same length, and that length is in between the length of C-C and C=C bonds?.. 0.139 according to the book..
    What about the Kekule model, what does that say about the bond lengths, and what about C-C and C=C bond lengths in general?

    Thanks
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    (Original post by Kasam)
    Can someone explain the part about carbon-carbon bond lengths in:
    Kekule's model
    Benzene

    And also can you explain the actual lengths of C-C and C=C bonds in regular compounds, like alkanes/alkenes.

    The book is a little :confused: on this part, for me atleast.

    Thanks a bunch!
    If the actual structure of benzene were to be alternating double C=C and single C-C bonds, like in the Kekule structure, you would expect there to be two different bond lengths in benzene.

    However, spectroscopic studies show that there is only one C-C bond length.

    In benzene C-C is 0.139 nm

    normal C-C bonds are 0.154 nm
    and C=C bonds are 0.134nm

    hence the bond length in benzene is intermediate between single and double bonds.
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    (Original post by Kasam)
    Can someone explain the part about carbon-carbon bond lengths in:
    Kekule's model
    Benzene

    And also can you explain the actual lengths of C-C and C=C bonds in regular compounds, like alkanes/alkenes.

    The book is a little :confused: on this part, for me atleast.

    Thanks a bunch!
    The carbon carbon bond lengths in Kekule's model are in between the lengths of an alkane and and alkene's bond length. This is unusual because Kekule suggested that there are 3 double bonds and 3 single bonds, therefore you would EXPECT there to be 3 bonds the same size and the other 3 bonds the same size but this isn't the case as all 6 c-c bonds in benzene are in between the length of an alkane and alkene's bond length.

    hope that helps!
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    Thanks to both of you, I think I get it now

    The book just had to explain it the difficult way! :rolleyes:

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Updated: April 7, 2012
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