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Resonance of HCO3^- and sigma/pi bonds

  1. Oct 30, 2006 #1
    Are two equivalent resonance forms HCO3^- like this?
    ........... O
    ..........//
    O - C
    .........\
    ......... O - H


    ..........O - H
    ........./
    O - C
    .........\\
    ...........O


    Both structures have brackets and a -.
    Also, each O on the left has six dots, the O on the double bond has four, and the O on the H has four as well. Sorry about the ........ I didn't know how else to 'draw' them so they would line up.

    Are there four sigma and 1 pi?

    Thanks.
     
  2. jcsd
  3. Oct 30, 2006 #2
    The two structures you have drawn are not resonance structures. You have simply rotated the molecule 180 degrees along the horizontal axis. Try to remember that, when drawing resonance structures, only electrons can move (not atoms).
     
  4. Oct 30, 2006 #3
    Thanks Geoff... In that case, I'm quite confused.
     
  5. Oct 30, 2006 #4
    Keep the molecule oriented the same in all resonance structures. In other words, the H must stay on the same O.

    What level of chemistry is this question from? Are you required to list only major resonance structures, or all of them?
     
  6. Oct 30, 2006 #5
    Thanks for the help so far, Geoff. I am only supposed to list two equivalent (I assume that might be the key word there) resonance forms.
    it's from first year university chemistry - just very out of my element.

    ........... O
    ..........//
    O - C
    .........\
    ......... O - H


    ..........O
    ........./
    O - C
    .........\\
    ...........O -H

    Is that what you are indicating?
     
  7. Oct 30, 2006 #6
    Although these are resonance structures, they are certainly not equivalent.

    Why do you think the double bond will shift to the O with an H attached?
     
    Last edited: Oct 30, 2006
  8. Oct 30, 2006 #7
    Try rotating the molecule so that the alcohol is pointing to the left.

    Code (Text):

         O
        //
    H-O-C
         \
          O
     
    Give the equivalent resonance structure of the molecule. I'll assume you can see it now.
     
    Last edited: Oct 30, 2006
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