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Distance between atoms in a bond

  1. Aug 28, 2015 #1
    Here's the question:

    The structure of 1,3-butadiene is usually written as H2C=CH–CH=CH2. The average bond lengths given in Table 9.2 in my textbook are: C–C of 154 pm and C=C of 133 pm. Explain the fact that the observed value of the distance between the two central carbon atoms in 1,3-butadiene is 146 pm.

    Are the 2 central carbon atoms the 2 carbons that have a double bond between each other? If so, the distance of C=C is equal to 133pm so why would the distance between the 2 central carbon atoms that are double bonded be different? How else would I answer this question? THanks.
     
  2. jcsd
  3. Aug 28, 2015 #2

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    Number the carbon atoms from 1-4, beginning to end of chain; "central" means "middle" of chain.
     
  4. Aug 28, 2015 #3
    so the central carbon atoms would be the ones in CH-CH. But I'm still not getting why the distance between these would be different than the given C-C distance.
     
  5. Aug 28, 2015 #4

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    You've seen/read a discussion of sp2, and/or sp3 hybrid orbitals?
     
  6. Aug 28, 2015 #5
    yeah i have, maybe its super obvious and i'm not seeing the connection?
     
  7. Aug 28, 2015 #6

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    What are the hybrids for 1, 2, 3, and 4?
     
  8. Aug 29, 2015 #7

    Borek

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    Google conjugation.
     
  9. Aug 30, 2015 #8
    1 would be sp2, assuming it has 2 bonds to H and one double bond to C2
    2 would be sp2, assuming it has 1 double bond to C1, 1 bond to H and another bond to C3
    3 would be sp2, assuming it has 1 bond to C2, 1 bond to H and one double bond to C4
    4 would be sp2, assuming it has one double bond to C3, and 2 bonds to H
     
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