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Organic Chem: Energy Barriers to Rotation

  1. Mar 1, 2008 #1
    I have a lab question that I'm stuck on.

    For your assigned molecule evaluate the energy barrriers to the rotation:
    from anti to gauche
    from gauche to gauche
    from gauche to anti

    I have data/graph of steric energy vs. dihedral angle of 1-chloropropane, but I don't know how to use this information to calculate the energy barriers. Any help is appreciated!
  2. jcsd
  3. Mar 2, 2008 #2
    As the dihedral angle is varied from 0 to 2pi, the steric energy curve exhibits
    a series of troughs separated by peaks. There should be a trough corresponding to the anti conformation and troughs at each of the gauche conformations. The energy barrier to go from one conformation to another is simply the height (relative to the energy of the conformation at which you are situated) of the peak that must be traversed to go from the first conformation to the second.
  4. Mar 3, 2008 #3


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    Sight your molecule along the C1-C2 axis. One carbon bears two hydrogens and a chlorine. The other carbon bears two hydrogens and a methyl group. Use a Newman Projection to help you visualize it. Hint: The highest peak will be from an eclipsing interaction between methyl and chlorine.
    Last edited: Mar 3, 2008
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