Talk:Molecular symmetry

message: I have been making some stylistic rewrites of this article for readability/tone and consistency, and will probably continue to do so.  Leave a note if something I do looks or reads silly.  Baccyak4H (Yak!) 16:09, 18 October 2007 (UTC)
replies: text: Overall the article is much improved after your edits. I have made a few (4) more revisions. Dirac66 01:55, 19 October 2007 (UTC)
replies: text:  Thanks for the feedback and the continued improvement.  "Matrixes"...  :-)  Baccyak4H (Yak!) 02:19, 19 October 2007 (UTC)
thread_title:  Some work 

message: In the symmetry groups section
I think Thionyl chloride is not planar, please edit  — Preceding unsigned comment added by 94.7.221.165 (talk) 12:15, 29 September 2011 (UTC)
replies: text: Thank you for pointing this out. The word "planar" in the description is misleading as it incorrectly suggests that the molecule is planar. The correct geometry is shown at the article Thionyl chloride. The symmetry group is in fact Cs as the article says, but the mirror plane is the plane which bisects the Cl-S-Cl angle, with one Cl on each side of the plane. I will change the verbal description to read "Mirror plane, no other symmetry". Dirac66 (talk) 12:55, 29 September 2011 (UTC)
thread_title: Thionyl chloride

message: For the big table: in my view, ChemDraw images are superior to the images produced by molecular modeling programs. ChemDraw images are just easier to visualize.  I sympathize with our wish to impress readers with beautifully colored images; they impress me too.  But maybe we should consider one prosaic ChemDraw image per pt group. --Smokefoot (talk) 02:12, 30 March 2021 (UTC)
replies: text: I agree it is cluttered at present. If by ChemDraw images you mean skeletal formulae, I think they would be a good addition to the table. However I don't think they should replace all the 3D images. The benefit of 3D over skeletal for both novices and experienced chemists is 3D is less abstract. It doesn't require as much mental processing or prior knowledge for a reader to understand what three-dimensional shape is being described, and that is clearly important in this article. --Ben (talk) 18:04, 30 March 2021 (UTC)
thread_title: ChemDraw

message: Isn't it true that point groups are said to be applicable to molecules even if the molecule is not necessarily always in a conformation that has that symmetry, from a strict geometrical point of view? For example, in the article we say  that meso-tartaric acid has inversion symmetry. But that's only strictly true if it's in a particular conformation. If it gets twisted this way or that, then it no longer has inversion symmetry, but we can still apply the term to the molecule. I believe the symmetry "up to" conformation is useful in calculating the entropy. Can someone confirm what I'm saying? Can we put something in the article about this? Eric Kvaalen (talk) 19:14, 23 October 2021 (UTC)
replies: text: The usual point group assignment assumes that the molecule is at its equilibrium geometry corresponding to a potential energy minimum. Asymmetric vibrations lower the symmetry, not only for meso-tartaric acid but even for molecules as simple as water which has an asymmetric stretch, and CO2 which has a bending vibration as well as an asymmetric stretch. The only molecules with no asymmetric vibrations are diatomic molecules. The article considers the question in the final section on Molecular nonrigidity. Dirac66 (talk) 21:06, 23 October 2021 (UTC)
replies: text:  Yes, I know all that, and I did see that final section, but I found it a bit arcane. My question is, shouldn't we say near the beginning that we often or usually assign point groups to molecules based on the way moieties are attached to them, not on whether they are geometrically exactly in a conformation that has the symmetry in question. For instance we say that meso-tartaric acid has inversion symmetry, even if it doesn't always, from a geometrical point of view. Here's another example: Let's say there's a compound tetra(chloro-fluoro-methyl)methane. If the chloro-fluoro-methyl groups all have the same chirality, then I think we would say that the molecule has (chiral) tetrahedral symmetry (denoted "T"), even if the side groups at any point in time may not be rotated exactly the same way, and consequently the symmetry elements of T are not in force. (I realize that quantum mechanically we can't really say that the molecule has a particular conformation at a given point in time -- there's a multidimensional wave function obeying the Heisenberg uncertainty principle.) Eric Kvaalen (talk) 05:04, 24 October 2021 (UTC)
thread_title: Conformation

message: The last section on Molecular rotation and molecular nonrigidity refers to a "double group". I cannot find the term "double group" defined anywhere on Wikipedia. Searching Wikipedia for an article "double group" leads to a redirect to "space group", but that article does not contain the words "double group". Also it refers to crystal symmetry including translation in space, rather than molecular symmetry about a point. Could someone add (here or elsewhere with a link from here) an explanation of what is meant by a "double group"? Could it be related to a direct product of groups?  Dirac66 (talk) 17:57, 5 March 2022 (UTC)
replies: text: There is a citation (Ref 25) to an article in the Journal of Chemical Physics in that section; the abstract mentioned that a "double group theory" due to Hougen is used to separate "torsional and a-rotational motions." I agree that it does bear some explanation if it's to be mentioned here, currently it's unclear. I can't access the original article to read further. KeeYou Flib (talk) 20:02, 5 March 2022 (UTC)

text: Actually I just found this; might shed some light. https://www.google.com/books/edition/Chemical_Group_Theory/f8b7ck4NQ8YC?hl=en&gbpv=1&dq=Hougen%27s+double+group+theory&pg=PA158&printsec=frontcover KeeYou Flib (talk) 20:03, 5 March 2022 (UTC)
replies: text: I see the "double group" also in the context of molecules having half-odd-integer electron spin (usually ions or radicals) such that that rotation by 2π results in negating the wavefunction. The group is twice as big and the character table is extended and has a new operator R for rotation by 2π. I don't understand it well and this book may help: section 7.6 of http://www.matfys.lth.se/education/FYS256/aryasetiawan.pdf. Also I see that Point group#List_of_point_groups speaks of doubling but has little explanation or references; I've want to understand that, and would like to know how these "double groups" are related. –MadeOfAtoms (talk) 01:19, 6 March 2022 (UTC)
thread_title: Double group?