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How to determine if all C atoms are coplanar

  1. May 7, 2016 #1
    1. The problem statement, all variables and given/known data
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    2. Relevant equations


    3. The attempt at a solution
    I can see that in B, not all C atoms are coplanar , but for C, D and E I can't see how the carbon atoms are coplanar .. I thought they are tetrahedral?
     
  2. jcsd
  3. May 7, 2016 #2

    Borek

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    Staff: Mentor

    In E carbon atoms are not coplanar (that is, one of them can "freely" move, so there will be moments when it will be complanar with others).

    How many carbon atoms in D? Can you think of such an arrangement of these atoms that they would not lie on a one surface?

    When it comes to C it would be best to see a model. Yes, all these carbons are sp3 hybridized, but it doesn't stop them from lying on one surface. Is the central COCO ring flat?
     
  4. May 7, 2016 #3
    Is it the carbon atom in CH3 that is free to move? What about the carbon atom bonded to No2?
    Like in their examples, all carbon atoms in benzene lie in a plane because they all use sp2 orbitals and every bond angle is 120°, right? But in the case of cyclohexane, all carbon atoms are sp3 hybridised and they each have a tetrahedral shape, so why can't they all lie in the same plane? How do you know if all carbon atoms can lie in a plane?

    3 carbons. Erm, is it like the arrangement of methylpropane ? Again, I am still confused, why the carbon atoms in methylpropane are not coplanar...

    I'm not sure.. Yes?
     
  5. May 8, 2016 #4

    Borek

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    Yes.

    Atoms in the ring are sp2, that means all atoms bonded to the ring lie in the ring plane.

    But they are - any three points always lie on a surface (technically that hold even when they colinear, even if there are infinitely many such surfaces then).

    Yes, the central COCO ring is rigid. That means all carbons sticking out of the C atoms must lie in a plane.

    I am afraid if you don't see it it won't be easy to show without a model. All carbons lie on a plane, and O atoms stick up and down, this is a rigid arrangement.

    Perhaps try to think about it this way - this molecules consist of two halves, each one containing three carbon atoms and connected by the oxygen bridges. Both halves contain three carbons, so these three carbons have to be coplanar (remember? each connected three carbons lie on a plane). Now, the way these halves are bonded through the oxygen bridges puts these carbon planes in the same place - so there is in fact one plane only.
     
  6. May 8, 2016 #5
    Ahh I see.. That was clear, thanks so much !
    But why is it impossible for the carbon atoms in methylpropane to be coplanar?
     
  7. May 8, 2016 #6

    Borek

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    There are four carbons - any three will be coplanar, but the fourth must stick out.

    As I said earlier, try to build models - even from putty, or plasticine, and matches/toothpicks.
     
  8. May 8, 2016 #7
    Ok, thank you !
     
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