Molecular symmetry group of non-rigid molecules

In summary: There is no formal way to do this. However, you could try to find the eigenstates of the molecule by using the Schrodinger equation and then looking for those states which have the lowest energy.
  • #1
Konte
90
1
Hello everybody,

I have read some very interesting book (Molecular symmetry and Spectroscopy - Bunker and Jensen) that talk about how to find the Molecular Symmetry group (MS) of a molecule by using the concept of "feasible" operation from the Complete Nuclear Permutation Inversion (CNPI) group.
Following the explanation given by the authors, "feasible" operation is that can interconverts a numbered and equivalent equilibrium versions of the molecule (rigid or non-rigid).

Confident of this understanding, I tried and success on finding MS of some famous non-rigid molecule until I met certain hard case as of the butane molecule which have non equivalent equilibrium versions!

So, my question is :

How to define the MS group of such a non-rigid molecule that have non equivalent equilibrium versions, knowing that between theses non equivalent equilibrium versions, potential barrier is not too high and allow some interconversion between the different versions of the same molecule?

I attached here the potential energy of butane as an example of those molecule which have more than one equilibrium versions:

butane-config.png


Thank you very much everybody.

Konte.
 
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  • #2
What's the ultimate goal? If it is spectroscopy, then the answer would be that you will find that the spectrum shows characteristics of both stable conformers.
 
  • #3
DrClaude said:
What's the ultimate goal? If it is spectroscopy, then the answer would be that you will find that the spectrum shows characteristics of both stable conformers.

My goal is to construct the character table of the MS group and from that be able to find selection rules.
Your answer suggest that I have to consider both stable conformers as an independent (different) molecules?

Thanks .

Konte
 
  • #4
There are no elements of the CNPI which would link energetically different minima of the potential energy surface.
 
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Likes Konte
  • #5
DrDu said:
There are no elements of the CNPI which would link energetically different minima of the potential energy surface.

Ok. Is there a formal way which permit me to characterize the eigenstates (with or without solving the Schrodinger equation) of such a molecule and having some selection rules?

Thanks.

Konte.
 

Related to Molecular symmetry group of non-rigid molecules

1. What is the molecular symmetry group of non-rigid molecules?

The molecular symmetry group of non-rigid molecules refers to the set of symmetry operations that can be performed on the molecule without changing its overall shape. This includes rotations, reflections, and inversions.

2. How is the molecular symmetry group determined for non-rigid molecules?

The molecular symmetry group of non-rigid molecules is determined by examining the arrangement of atoms and bonds within the molecule. The presence of certain elements, such as carbon-carbon double bonds, can affect the symmetry and lead to different possible symmetry groups.

3. What impact does the molecular symmetry group have on a molecule's properties?

The molecular symmetry group can give insight into a molecule's physical and chemical properties. It can affect the molecule's stability, reactivity, and spectroscopic behavior. Molecules with higher symmetry may also have certain degenerate energy levels, making them more stable.

4. Can the molecular symmetry group of non-rigid molecules change?

Yes, the molecular symmetry group of non-rigid molecules can change depending on external factors such as temperature, pressure, or interactions with other molecules. For example, a molecule that exhibits rotational symmetry at room temperature may lose this symmetry at a higher temperature due to molecular vibrations.

5. How is the molecular symmetry group of non-rigid molecules used in chemistry?

The molecular symmetry group is used in chemistry to predict and understand a molecule's behavior and properties. It can aid in the determination of molecular structures, the interpretation of spectroscopic data, and the prediction of chemical reactions. Additionally, it can be used to design experiments and synthesize molecules with desired properties.

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