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What is the geometry of dichloromethane?

  1. Oct 24, 2008 #1
    organic chem!!

    What is the geometry of dichloromethane?? Before optimization, Cl-C-Cl bond is 109.5, H-C-Cl bond is 67.8... so it must be tetrahedral... but after optimization, do the angles get bigger?? why?
    and also, the bond length increases...
    Why do angles and the bond length in dichloromethane increase when it's geometrically optimized??

    Another question is...
    when we examine (E)-1,2-diisopropylethene, (Z)-diisopropylethene, and 1,1-diisopropylethene... the molecular energies are different. (E) isomer has the least energy, so it's more stable and the 1,1-isomer's the least stable... i think...? why??? does it have to do with how the bulky groups are far apart or not??
    The most confusing part!!! is how the bond angle for these isomers are in a weird order.... E has the smaller angle, and Z has the biggest.... I can't figure out why!!! > . <
     
  2. jcsd
  3. Oct 24, 2008 #2

    GCT

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    Re: organic chem!!

    Are you accounting for the influence of electronegativity and electron density?

    Do you know about the concept of hyperconjugation?

    What bond angles are you referring to specifically?
     
  4. Oct 24, 2008 #3

    chemisttree

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    Re: organic chem!!

    Bond angles change (from an ideal tetrahedron) for what reason? What bond length did you start from? The bond length for C-H?

    Yep.
    What angle are you measuring? The angle between the double bond and the IPr group or between the vinyl carbon's hydrogen and it's IPr group?
     
  5. Oct 24, 2008 #4
    Re: organic chem!!

    1. Does the bond angle change to reduce steric strain maybe?? and we measured the C-Cl bond length which was about 1.76 whereas after optimization, it went up to about 1.79A.
    So again, does making the bonds be farther apart make it more stable??

    2. ok the bond angle of C=C-C was measured for the three isomers..
    so in increasing order it was E<1,1-ipr<Z... this doesn't quite make sense for me...
     
  6. Oct 24, 2008 #5

    chemisttree

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    Re: organic chem!!

    Bigger groups like Cl don't like to be as close together as smaller groups like H.

    You can think of the IPr group as a big bulky thing that is pushing against its neighbor groups. It pushes against the geminal hydrogen and the other vinylic groups on the other carbon. You have to come to grips with the fact that hydrogen is small relative to IPr and that the vinyl (=CH2) carbon is smaller than IPr but bigger than hydrogen.
     
  7. Oct 25, 2008 #6
    Re: organic chem!!

    hmm i'm confused... aren't the IPr groups for all three isomers pushing against =CH2 regardless of how they're arranged?
     
  8. Oct 25, 2008 #7

    Borek

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    Re: organic chem!!

    You have =CH2 in only one of the isomers.
     
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