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Hydrogen bonding in ethanol

  1. Nov 13, 2012 #1
    Hey,

    How do you know how many hydrogen bonds ethanol molecules will form with each other? I know there are 3 sites where H bonds could form (2 lone pairs on oxygen and the hydrogen) but with something like hydrogen fluoride, each molecule only forms 1 H bond on average so shouldn't something similar happen with ethanol since each has only one hydrogen bond to 'donate'?

    Thanks :)
     
  2. jcsd
  3. Nov 13, 2012 #2

    AGNuke

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    Check the definition of Hydrogen Bonding at wikipedia. H-Bonding is a special, stronger case of dipole-dipole attraction. The bond is slightly polarized, which may be seen as an electric dipole of some small "charge".

    In HF, F has slight negative "charge" and H has an equivalent positive "charge", so F only forms one H-Bond.

    But in Ethanol, O has more negative charge than H has positive charge (Ethyl group has +I effect) so overall, O-atom can enough polarization to form two H-Bond.
     
  4. Nov 13, 2012 #3
    Thanks for replying :) I've just read Wikipedia's entry but I think I must still be missing something :/

    I understand the +I effect and how the O-atom can form two H-bonds, but the H-atom also forms a H-bond with an O lone pair on another ethanol doesn't it? So does that mean each molecule forms 3 H-bonds then? :S
     
  5. Nov 13, 2012 #4

    AGNuke

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    You may check this figure. It says something else.
    800px-Ethanol-xtal-1976-3D-balls.png
     
  6. Nov 14, 2012 #5
    Yeah I mean I know that my idea of how it might bond is wrong but I'm just not sure of exactly what makes it different :confused:

    So in your picture, for one molecule of ethanol (on average): one lone pair on the O-atom 'accepts' a H-bond from another molecule, and one of it's H-atoms 'donates' a H-bond to another molecule's lone pair, giving 2 H-bonds per molecule?

    I just want to check that's right first :)
     
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