Talk:Cahn–Ingold–Prelog priority rules

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how to assign R,S configuration to a chiral centre which is the more correct method- by performing even no. of exchanges (converting wedge formula into 2D) or in a 3D formula —Preceding unsigned comment added by 61.17.123.146 (talk • contribs)

any illustrations that could be added would greatly enhance the effectiveness of this explanation. R- and S- configurations are a highly spacial/visual concept, and in this case, I believe a picture is worth more like 5,000 words. —Preceding unsigned comment added by 129.237.40.188 (talk • contribs)

The current explanation of the priority rule indicates that one exhausts the highest priority branch completely before considering any of the others. This appears to be at odds with Cahn, Ingold, and Prelog's original paper, which I read this morning and for which I added a reference. The authors' explanation uses a series of "sets" (really passes), each of which considers atoms one unit farther from the stereocenter than the previous pass. Any difference found in a pass breaks a tie, regardless of whether it is on the highest-priority branch. For example, consider the groups -CH(NH-CH2-Cl)(CH3) and -CH(NH-CH3)(CH2-Br). The Wikipedia procedure declares the first group higher priority because of the Cl, but the authors' procedure declares the second higher priority because of the Br (it is closer to the attachment point than the Cl). Unless I hear an objection, I think I will replace the current explanation with my own based on the original paper. Hashproduct 17:45, 5 October 2007 (UTC)


 * I went ahead and rewrote the explanation of priorities from my understanding of the original papers, making it much more thorough. It's possible that I am mistaken about some points or have made careless errors in the examples.  If you believe I am wrong about a major point, go ahead and redo the explanation if you like, but please discuss the issue with me so we can make sure the article ends up saying the correct thing according to the official definition of the system.  I took the opportunity to improve the article in some other ways at the same time. Hashproduct 05:21, 13 October 2007 (UTC)


 * Good job. The rules seem correct and readable enough to me, but I then I knew them already. ;-) I think that the article could be made much easier to understand if it had some figures, especially about the use of ghost atoms. --Itub 09:46, 13 October 2007 (UTC)

Use in Inorganic chemistry
The CIP rules are also used in inorganic coordination complex naming to prioritise the ligands as part of assigning the configuration index. Can this be added?--Axiosaurus (talk) 16:45, 21 March 2008 (UTC)

"-CH(OCH3)CH3 > -CH(OH)CH2OH. The distance-2 lists are both (O, C, H), a tie. Replacing each atom with a list of its neighbors, we obtain the distance-3 lists: ((C), (H, H, H), ) and ((H), (O, H, H), ). The earliest difference is in the atom bonded to the distance-2 oxygen: -CH(OCH3)CH3's carbon outranks -CH(OH)CH2OH's hydrogen. It is irrelevant that the oxygen in the second list outranks the corresponding hydrogen in the first list." Is this right? Should'nt the distance 3 Oxygen outrank any of the other atoms, since the atomic number of the Oxygen is bigger than any of the atomic numbers of the other distance 3 atoms? —Preceding unsigned comment added by 213.22.32.210 (talk) 12:40, 14 April 2009 (UTC)

No, you first have to look to the neighbors of O in the distance-2 list (O, C, H), if these neighbors were the same you were right. But the neighbors of O are not the same in both structures. The O in the first structure has C as neighbor, and the O in the second structure has H as neighbor. C outranks H. Therefore it’s true what is written.--Damian echo (talk) 14:53, 28 April 2009 (UTC)


 * -CH(OH)CH3 > -CH2OH. The directly attached atoms are both carbon, but the distance-2 lists differ: they are (O, C, H) and (O, H, H), respectively.  The earliest difference is in the second slot, where the carbon atom of -CH(OH)CH3 takes priority over the hydrogen atom of -CH2OH.

The text is correct, but in the last structure (-CH2OH ) at the end of the text another H should be made bold. Because it’s not the H in OH what it’s about. The reason you take the second slot instead of the first slot is because the first slot is identical, both OH. The H made bold should be the one attached to the distance-1 C, not to the O.

The last structure should be:

–CHHOH (instead of -CH2OH) I’m putting the two H’s separate to emphasize it’s only one of them which is important. Otherwise it will be -CH2OH and that’s not correct. I want to change this in the text but this is my first contribution to Wikipedia, because of this I’d like someone to confirm this first. Thank you.--Damian echo (talk) 15:16, 28 April 2009 (UTC)

Remove section of "Buergenstock Declaration"?
The Buergenstock Declaration, signed by Cahn, Ingold, and Prelog, as well as 2 others attending the stereochemistry conference held in Buergenstock, Switzerland in 1966, does not appear to have had any role in "laying down the rules" of the CIP conventions. These were put forth in the articles referenced elsewhere on the page. A facsimile displayed on this site shows the Declaration to be a jest among friends. Written in a style parodying official agreements, it declares the CIP system to be "just" and "fair" and commits the signatories to strict adherence to the rules on pain of footing the bill for a round of drinks for the first infraction and of a complete reading of the original articles on subsequent ones. It carries no official status or historical weight. I suggest that the section be removed. At least it should be rewritten to indicate the true nature of the document, but I would argue that it is more appropriate to the biographical pages in Wikipedia for the signatories, especially that of Prelog, who was apparently a man of wit and good humor.

Perhaps someone can confirm that there does or does not exist another, truly official, Declaration, of which I am unaware. Also lacking access to what would appear to be the primary reference for the "document" above: Prelog, Vladimir, "My 132 Semesters of Chemistry Studies" (J. Seeman, ed., American Chemical Society, 1991), I have not changed the article yet. -- Jmcclaskey54 (talk) 02:10, 6 March 2010 (UTC)


 * Thanks for bringing this to our attention. For now I have removed the section V8rik (talk) 20:34, 8 March 2010 (UTC)


 * Glad to help. I now notice that there is a redirect to this page from "Buergenstock Declaration". Should this redirect not be deleted as the reader will find no reference to it in the target? Is it enough that reference to it is made on this talk page? The Wikipedia statement on reasons to delete redirects does not explicitly address this circumstance, but there is no relevant page history on the redirect page. I have nominated the redirect for deletion. Could it be converted to a stub? I defer to others, but I do not believe that it is notable enough to warrant an article. No mention is made of it in the articles on Prelog, Ingold, or Cahn. A Google search yields only the page noted above, another page with a portion of the Prelog memoir TOC, and multiple links to this article. Jmcclaskey54 (talk) 00:41, 15 March 2010 (UTC)


 * Nomination for deletion of redirect withdrawn. For reasons given above, I am not sure this topic rises to a level of notability that warrants mention in Prelog biography (or those of other signatories), but obviously the resolution of the question is prior to consideration the redirect deletion. In my opinion it would not be enough to simply supply the external link with no elaboration. Again, for now I would defer to others (members of WikiProject Chemistry, say) to determine notability, though a reading of the Prelog memoir would shed much light on the matter. I will try to obtain a copy, and if warranted, I'd be happy to add something to the Prelog article on it. In the meantime, should the redirect be transformed into a stub, which could later be merged? General advice on how to handle similar issues in future appreciated. Thanks. Jmcclaskey54 (talk) 19:35, 15 March 2010 (UTC)

Carvone example
The following was posted as an edit summary by User:24.68.37.35. "The carvone example is wrong. The oxygen atom gives priority to that group, this molecule is in R not S. Source, pearson text book that I'm currently looking at.)"


 * My response: The assignment looks right to me. It seems that Sigma-Aldrich would also label this as S-Carvone.  I can only conclude that the Pearson book is wrong.  BTW, I have taught organic chemistry for the past 17 years.  The isopropenyl group is clearly #1 and the H is clearly #4.  For the other two, you go -CH2-C(=O)-C on the right side, and CH2-C(=C)-C on the left.  The difference comes down to either C=O (on right) vs. C=C (on left).  Since O has a higher atomic mass than C, it ranks as higher priority, making the right hand side of the ring #2.  That makes the overall structure S as you go #1 -> #2 -> 3.  Does that make sense, or have I missed something important here?


 * Also, thank you very much for your edit! It's feedback like this that ensures errors in Wikipedia get fixed.  It's a shame we can't fix the book in the same way! Thanks, Walkerma (talk) 18:28, 15 October 2015 (UTC)

Wiki Education assignment: Honors Organic Chemistry I
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