Organic Chem: Energy Barriers to Rotation

In summary, the conversation is about evaluating the energy barriers for the rotation of 1-chloropropane from anti to gauche, from gauche to gauche, and from gauche to anti conformations using the steric energy curve. The peaks on the curve represent the energy barriers to go from one conformation to another, and the highest peak is caused by an eclipsing interaction between the methyl and chlorine groups. A Newman Projection can be used to visualize the molecule and its conformational changes.
  • #1
sam.
16
0
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!
 
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  • #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.
 
  • #3
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.
 
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Related to Organic Chem: Energy Barriers to Rotation

1. What is the concept of energy barriers to rotation in organic chemistry?

The concept of energy barriers to rotation in organic chemistry refers to the energy required for a molecule to rotate around a specific bond. This energy barrier is caused by the presence of other atoms or functional groups in the molecule, which can hinder or prevent rotation.

2. How do energy barriers to rotation affect the stability of a molecule?

The presence of energy barriers to rotation can affect the stability of a molecule by making it more difficult for the molecule to adopt a lower energy conformation. This can lead to a less stable overall structure and potentially impact the molecule's reactivity and functionality.

3. What factors contribute to the magnitude of energy barriers to rotation?

The magnitude of energy barriers to rotation is influenced by several factors, including the type of bond (single, double, or triple), the size and shape of the substituents attached to the bond, and the strength of the bonds in the molecule.

4. How can energy barriers to rotation be overcome?

Energy barriers to rotation can be overcome through the application of energy, such as heat or light. This can provide enough energy for the molecule to break through the energy barrier and rotate around the bond. Enzymes and catalysts can also help to lower the energy barrier and facilitate rotation.

5. What are the implications of energy barriers to rotation in drug design?

Energy barriers to rotation play a significant role in drug design as they can affect the bioavailability and potency of a drug. By understanding and manipulating the energy barriers, chemists can design more effective and selective drugs with improved pharmacological properties.

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