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Topic: Point Group  (Read 26783 times)

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Offline Dolphinsiu

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Point Group
« on: April 21, 2008, 08:31:59 AM »
Actually I only would like you to check whether my answer is right or not in the following questions:

Determine the point group of the following compounds:

PF5: D3h
Staggered form of ethane: D3v
[Co(en)3]3+: D3
NH3: C3v
1,3,5,7-tetrafluorocyclooctatetraene: C2

Offline Alpha-Omega

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Re: Point Group
« Reply #1 on: April 21, 2008, 12:00:24 PM »
In order to verify these you will have to perform the symmetry operations and determine which group each molecule belongs to. 

That is why I directed you to the interactive symmetry sites where you can make those determinations interactively.

Your other option is to build the models with a molecular model kit and perform the indicated operations for the point groups and validate the group to which each of your species belongs.

You have to classify these molecules to their respective point groups by performing the symmetry opearations.


"PF5: D3h"

The PF5 molecule structure belongs to the D3h  symmetry point group. Its major axis is C3, which gives you the number 3 for the point group. It has a C2 axis perpendicular to the major C3, so it is D group. It has σh plane symmetry, so it is D3h.


“Staggered form of ethane: D3v

For the staggered form of ethane I think you mean D3d (I think that D3v is a typo?).

The staggered C2H6 molecule structure belongs to the D3d point group. Its major axis is C3, which give us the number 3 for the point group. It has a C2 axis perpendicular to the major C3, so it is D group.  It has no σh plane, but it does have σ plane symmetry, so it is D3d.

You can also verify that here (just perform the symmetry operations to verify the point group D3d 

http://www.phys.ncl.ac.uk/staff/njpg/symmetry/Molecules_l3d.html


"[Co(en)3]3+: D3"

In order to validate that this molecule belongs to the D3 point group you will have to validate the following:

1. Linear, low symmetry or high symmetry? No
2. Cn axis? Yes- Principal axis C3
3. nC2 axes perpendicular to C2? Yes
4. σh? No
5. σd? No

D3 applies for "[Co(en)3]3+


“NH3: C3v

The Point Group Cnv:

In general, molecules in the point group Cnv all have a principal axis of rotation, Cn, but unlike the Dn, Dnh, and Dnd groups, do not have nC2 axes at right angles to it. Many common molecules belong to this point group, including H2O, NH3.

You can check the NH3 here (just run thru the operations to verify the C3V point group): 

http://www.phys.ncl.ac.uk/staff/njpg/symmetry/Molecules_l3d.html

"1,3,5,7-tetrafluorocyclooctatetraene: C2"

In order to validate that this molecule belongs to the C2 point group you must show the following:

Molecule possesses one axis of symmetry only (C2) plus it possesses no other elements except C2.
« Last Edit: April 22, 2008, 09:30:45 PM by Alpha-Omega »

Offline Dolphinsiu

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Re: Point Group
« Reply #2 on: April 21, 2008, 12:48:28 PM »
Thanks a lot, Alpha-Omega! ;D

Offline Alpha-Omega

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Re: Point Group
« Reply #3 on: April 21, 2008, 01:33:05 PM »
NP  ;)

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