Introduction to Symmetry Operations and Point Groups
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- Опубликовано: 5 июл 2024
- In this short educational video, Rosie Lester introduces us to symmetry operations and symmetry elements and point groups. The focus of the video is on small organic molecules for an easy visualisation.
Rosie demonstrates the effects of identity, inversion, rotation, reflection, and improper rotation symmetry operations on representative molecules, for example showing symmetry operations for benzene. Then, we will see how to determine point groups thanks to the symmetry operations identified using a flow chart. You can then test yourself on symmetry operations, elements, and point groups with example molecules.
In this video:
- 01:18 Brief introduction to symmetry operations and associated symmetry elements (including: 04:18 Symmetry operations for benzene)
- 08:07 Flowchart to determine point groups based on the symmetry operations.
- 08:23 Challenge yourself! Identify symmetry operations and point groups using the chart. The answers are included in the video.
Resources:
On our website you can find the transcript of this video as a worksheet as well as the flowchart, which can be used for teaching and reviewing. The document contains links to further resources.
You can also find practice exercises on point groups in the module "Learning Point Group symmetry through 3D printed models".
www.ccdc.cam.ac.uk/Community/...
The molecules used to demonstrate these concepts are available in the Cambridge Structural Database (CSD). In particular, we used CSD Entries: FULLER, BENZEN, AYALOC.
You can visualise and download the structures for free from CCDC's Access Structures service: www.ccdc.cam.ac.uk/structures/
Water, hydrogen cyanide, CHFBrCl, and ethane were instead manually sketched in Mercury, but you can use ConQuest, the CSD searching software (licenced), or Access Structure (free) and WebCSD (licenced), to find structures containing these molecules.
The images and animation frames of these molecules are prepared using Mercury. Mercury visualisation software is available to download for free www.ccdc.cam.ac.uk/solutions/...
In Mercury you can also visualise symmetry elements on the crystal structure.
More advanced functionality from the CCDC enables you explore molecules and structures in more detail. To find out how to access more advanced functionality with a CSD-Core license see www.ccdc.cam.ac.uk/solutions/...
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Amazing help! Symmetry can be a mind bender and there are very few good videos on the matter. Cheers :)
You just saved my life for an exam I have today, lecture notes and office hours haven't helped at all, but this made it so much easier to understand.
Best of luck in your exam!
your explanation is just amazing.
Loved it. Thank you for the video.
This was so clear and easy to understand, thank you!
A very clear exposition of the principles of symmetry. I will show it to my students. But please do not confuse the words "principle" and "principal". You should refer to the C6 in benzene as the "principal" axis.
great video really good way of teaching
I've got a test tomorrow, and I keep messing up
Me too
Who doesn't 😂
Awesome demonstration.I have subscribed your channel.
Ah! I've just gotten used to H-M notation, now I need to learn Schoenflies!
The subscript on sigma seems hard to determine in for example para-dichlorobenzene. There are 3 2-fold rotation axes, so which becomes the "primary" rotation axis in this case?
I am currently reading through Atkin's Molecular Quantum Mechanics book. The chapter on Group Theory is awfully abstract and hard to visualize (at least for me). These animations help a lot. Thanks!
Realmente as figuras não são muito elucidadtivas nesse livro texto.
I wish I had that flowchart when I took undergraduate inorganic
still trying to get my head around horizontal and vertical planes of symmetry
could you explain why the planes are sigma d but not sigma v? your videos really help me a lot, thank you so much.
Just did this in class today. Basically sigma v is when the plane cuts along the z axis and sigma d is when it doesn’t.
In chemistry, sigma (σ) planes of symmetry are used to describe symmetry elements in molecules. The key difference between a sigma d (σd) plane of symmetry and a sigma v (σv) plane of symmetry lies in their orientation and the type of symmetry they represent:
1. Sigma d (σd) Plane of Symmetry:
- A sigma d plane of symmetry is a plane that bisects the molecule in such a way that it divides the molecule into two identical halves.
- This plane passes through the center of the molecule and is perpendicular to the principal molecular axis, which means it goes through the nucleus of the central atom.
- Sigma d symmetry is often associated with linear molecules, such as diatomic molecules like O2 and N2.
2. Sigma v (σv) Plane of Symmetry:
- A sigma v plane of symmetry is a vertical plane that passes through the molecule.
- This plane is perpendicular to the principal molecular axis and is parallel to one of the molecular bonds.
- Sigma v symmetry is typically associated with molecules that have a vertical axis of symmetry, such as planar molecules like benzene (C6H6).
In summary, sigma d planes of symmetry bisect the molecule perpendicular to the principal axis, while sigma v planes of symmetry are vertical planes that are parallel to molecular bonds. Understanding these symmetry elements is essential in the study of molecular symmetry and spectroscopy in chemistry.
if the ethane has a staggered structure would it be possible that it possesses a c6 axis rather than a c3?
Hi Ben,
Ethane does not have a C6 rotation axis. This is because if you are only rotating the molecule, you need a 120 degrees rotation to overlap with the initial structures, hence the C3 axis.
Ethane in a staggered conformation has also an improper rotation axis S6, where indeed the rotation is of 60 degrees, and then the rotation is followed by a reflection, hence overlapping with the initial structure.
For a more visual explanation, both the rotation and improper rotation axes are demonstrated on the molecule from 07:10 in this video and they can also be seen in the example on the Symmetry@Otterbein web resource symotter.org/tutorial/ethanes
I hope this helps!
CCDC Team
Tysmmmm
فوتي فالموضوع دغري تكفين الاختبار بعد كم ساعه
Where you are from?You are so nice at teaching.🎉
Inorganic?
Not enough information, the examples go through too quickly, couldn't follow properly.
Hi - we also have a PDF that walks through this topic. Click on "Introduction to Symmetry Operations and Point Groups" here: www.ccdc.cam.ac.uk/Community/educationalresources/teaching-modules/
Cant see the video clearly
Hello! If the video is not loading well on the device, you can find this introduction also in pdf format on our website. You can find it in the Teaching Modules webpage linked below, where you can download the resource: Introduction to Symmetry Operations and Point Groups.
Go here: www.ccdc.cam.ac.uk/Community/educationalresources/teaching-modules/