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London forces between benzene molecules

  1. Apr 12, 2010 #1
    How easily do benzene molecules interact with london forces?

    I imagine that the relatively large surface area of the aromatic ring coupled with the pi-ring, which is a pretty large orbital makes london forces of a pretty large magnitude possible, but I am not certain.

    Does anyone have any insight into this?

    Thanks in advance.
     
  2. jcsd
  3. Apr 13, 2010 #2

    alxm

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    Well, I'm not sure what kind of answer you expect to 'how easily'... They do certainly interact via london forces, just like everything else.

    Being nonpolar (and as you said, pi-conjugated) molecules, they certainly do interact, forming nice little stacks (cutely named pi-stacks!)
    I guess you could put it this way: You can't get an very useful description of the physical chemical properties of benzene without taking into account dispersion forces.

    And since I happen to have a relevant paper right here on my desk, here are some facts and figures:
    A benzene dimer with two benzenes stacked directly on top of eachother has a binding energy (due to London forces) of -1.8 kcal/mol at optimal distance, which is 3.70 Å.
     
    Last edited: Apr 13, 2010
  4. Apr 13, 2010 #3
    Thank you for your answer. I guess the wording "How easily..." was flawed. What I had in mind was information about how stongly they interact relative to other compunds.

    I found the figures you supplied to be quite ammusing, as I immagine a polymer of suck rings. I wonder what properties such a polymer would have?
     
  5. Apr 14, 2010 #4

    alxm

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    Well, it's not a very strong force keeping it together really.
    For comparison (which I should've given earlier), a single hydrogen bond is typically ~5 kcal/mol.

    I doubt you could make a really big stack, given the low energy involved, the forces of entropy would overcome it pretty quickly.
     
  6. Apr 16, 2010 #5

    chemisttree

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    It would have the property of a very low temperature thermotropic liquid crystal, very likely of the http://en.wikipedia.org/wiki/Liquid_crystal" [Broken] type.
     
    Last edited by a moderator: May 4, 2017
  7. Apr 17, 2010 #6
    The Hydrogen atoms in Benzene molecule are inactiv and usualy they are involved only in Electrophylic aromatic substitution mechanism. But uper or down Benzene ring electrons act all together and make some Mettalocenes sandwich aromatic compounds as
    Chromocene Cr(CH6)2.
     
  8. Apr 19, 2010 #7
    The interaction between molecules related to London forces is weak. But, the quantitative London interaction depends on the electronic structure of the molecules involved, i.e., for the simpler case, London forces depend on the ionization energy of the atoms.

    To study these interactions one should introduce a potential energy model like the simple point charge model or any of its modifications.

    Interesting question.
     
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