Talk:Hypervalent molecule

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CAt2H3?[edit]

Recently a (I believe theoretically) hypervalent carbon atom has been found, bonding to 3 hydrogen and 2 astate atoms. Is this worth mentioning? Source: http://www3.interscience.wiley.com/journal/122518352/abstract?CRETRY=1&SRETRY=0 82.72.78.101 (talk) 20:40, 15 November 2009 (UTC)

I believe that As is astatine. So this would happen: Anyone near the compound would get radiation poisoning from the astatine. The whole lab would be contaminated, and so would all the gloves, lab coats, and goggles. Astatine is extremely radioactive. Don't play with that stuff(unless you're trying to keep the lab to yourself). 03:41, 9 December 2016 (UTC)03:41, 9 December 2016 (UTC)03:41, 9 December 2016 (UTC)~ 32ieww (talk) 03:41, 9 December 2016 (UTC)

Shameful[edit]

This whole article is shameful. It departs from an obscure paper from 1969 that is not generally accepted in chemistry at all and makes statements that are blatantly untrue, e.g. that MO-theory assumes totally outdated and disproven things like sp3d hybridization. Modern MO-theory does not make a priori assumptions about hybridization at all, but combines atomic orbitals according to the irreducible representations (irrep) of the symmetry group at hand. Only if two molecular orbitals transform as the same irrep can there be mixing. For main group elements it has long been shown that d-levels are far too high in energy to make any contribution. Jcwf (talk) 15:55, 21 January 2010 (UTC)


  • Your edit summary is utterly offensive , do you really expect a comment? V8rik (talk) 22:44, 21 January 2010 (UTC)

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Pentacoordinated silicon[edit]

In the paragraph on Pentacoordinated silicon, as I read it, is a contradiction between the text accompanying the illustration:

  • Relative bond strengths in pentacoordinated silicon compounds. In A, the Si-O bond length is 1.749Å and the Si-I bond length is 3.734Å; in B, the Si-O bond lengthens to 1.800Å and the Si-Br bond shortens to 3.122Å, and in C, the Si-O bond is the longest at 1.954Å and the Si-Cl bond the shortest at 2.307A

and the text just below it:

  • Interestingly, complexes such as these provide a model for the SN2 transition state; the Si-O bonds range from close to the expected van der Waals value in A (a weak bond, representing an early SN2 transition state) almost to the expected covalent single bond value in C (a strong bond, representing a late SN2 transition state)

The way I read both sentences, the first is stating the oxygen-silicon bond lengthens going from iodine to chlorine, the second claims it to shorten. Who knows the correct answer?T.vanschaik (talk) 15:51, 25 May 2012 (UTC)

Good question. I have now checked the cited review article by Holmes. The bond lengths are as given by Holmes, except that ... the ring "carbon" which is beta to both O and Si should be a nitrogen (in all 3 molecules), so these structures need redrawing. However Holmes does not mention early and late SN2 transition states here, so this point is OR which contradicts the reference and should be removed. As for weak and strong bonds, Holmes says that the silicon-halogen value is close to a van der Waals value for A, so here again the article needs rewriting. When in doubt, check the original reference (if possible). Dirac66 (talk) 21:07, 25 May 2012 (UTC)
No reaction after 5 years(!), so I have now finally deleted the OR and changed oxygen to halogen. Perhaps someone with the proper software could redraw the structures as indicated above.Dirac66 (talk) 01:32, 4 July 2017 (UTC)

Kobs?[edit]

In the section on Reactivity the rate of the reaction is gviven in "Kobs, M−2s−1". Although the unit of this (or these?) "kobs" is given, what is it refering to? If it is an acronym, what does it mean? T.vanschaik (talk) 08:50, 29 May 2012 (UTC)

It'll be kobs, the observed rate constant, I assume. --Ben (talk) 10:19, 29 May 2012 (UTC)
Being puzzled with it for a day, I too reached that point. Never the less, it ensures me to translate it that way. Thanks.T.vanschaik (talk) 14:30, 30 May 2012 (UTC)

Merger proposal[edit]

The following discussion is closed. Please do not modify it. Subsequent comments should be made in a new section. A summary of the conclusions reached follows.
The result was do not merge. I take note the historical significance. But maybe some more emphasis on the non-bonding concept may be needed at the hypervalent molecule page.-- Officer781 (talk) 13:26, 4 April 2013 (UTC)

I propose that Three-center four-electron bond be merged into this article as the two are intrinsically linked; not only that, but the 3c-4e is only one of many types of hypercoordinate bonds, where molecules like sulfur hexafluoride are described by a 7c-12e bond. Therefore the 3c-4e is not an isolable bonding interaction like the 3c-2e which would then deserve its own article.--Officer781 (talk) 08:16, 27 March 2013 (UTC)

Support the merger. Comment lest we veer this direction: over-emphasis on absolutism ( "7c-12e" bond vs a collection of "3c-4e bonds") is the kind of over-precision that can wreck articles in terms of their understandability to normal readers. Chemistry is powerful because itis selectively sloppy with many concepts (so long as we are aware of our sloppiness).--Smokefoot (talk) 13:04, 27 March 2013 (UTC)
Agreed. I think the best would be to explain it from the basics: hypercoordinate bonds are bonds which have nonbonding orbitals in them. The attempts to break it down into terminology will over-emphasize the local interactions without the understanding of the concept. And though some authors like to break the sulfur hexafluoride bonds into three 3c-4e bonds, an examination of the molecular orbital diagram shows that there is an s-orbital interaction throughout all six bonds (of similar magnitude to all other molecules without an s-orbital lone pair such as methane) which cannot be described by the exclusive 3c-4e bond collection (of course together with the fact that the nonbonding orbitals also do not follow the same symmetries as implied by exclusive 3c-4e interactions).--Officer781 (talk) 03:14, 29 March 2013 (UTC)
The reason that 3c-4e is emphasized is historical as its description goes back to Pimentel in 1951. If it is merged into this article, it should at least have its own section in the article, followed by a second section for other similar bonding schemes. Dirac66 (talk) 13:13, 27 March 2013 (UTC)
I'd suggest we introduce the concept along with the 3c-4e and how Pimentel and Rundle proposed it (in the current 3c-4e article this history isn't elaborated upon). And then in the second section we derive the concept of non-bonding orbitals from there to apply to other molecules.--Officer781 (talk) 03:04, 4 April 2013 (UTC)
  • Terrible idea, the hypervalent article is really about hypercoordinated molecules and the article attempts to show how molecules deal with hypercoordination. The 3c-4e article describes one of many types of bonds. It fits nicely with 3c-2e and 4c-2e cousins. It could be trimmed down a bit. 3c-4e is not equivalent with hypercoordination. V8rik (talk) 18:05, 29 March 2013 (UTC)
But are there any instances where the 3c-4e is used outside of hypercoordination? Moreover, the 3c-2e and 4c-2e are distinctive interactions, while the 3c-4e is again, only one of many types of hypercoordinate bonds. --Officer781 (talk) 00:57, 30 March 2013 (UTC)
Hmm, on second thought, the 3c-2e and 4c-2e are related. They're both electron-deficient bonds, mostly used by boranes.--Officer781 (talk) 06:00, 30 March 2013 (UTC)
people interested in hypercoordinated molecules should not be bothered with the finer details of the three-center four-electron bond. Hypercoordination can live without 3c-4e but the reverse is not true, In this sense the topics are not interlinked. V8rik (talk) 17:04, 3 April 2013 (UTC)
But I don't get how the topics are not interlinked? How 3c-4e is not equivalent with hypercoordination (isn't it a subset of hypercoordination)?--Officer781 (talk) 03:02, 4 April 2013 (UTC)

The above discussion is closed. Please do not modify it. Subsequent comments should be made in a new section.

1. SF6 resonance structures - 12 or 15?[edit]

To Officer 781: have you a source for the comment (in your edit summary today) that 3 of the 15 resonance structures for SF6 are symmetry-forbidden? It is true that 3 structures are trans and the other 12 cis, so the trans structures will have a different (smaller? larger?) weighting in the overall wavefunction than the cis. However it is not all clear to me that the trans structures have zero weighting. Dirac66 (talk) 14:36, 4 October 2013 (UTC)

Hmm. That's a point then. Although the resonance structures on wikipedia don't seem to be exhaustive (eg. benzene doesn't include the Dewar structures). I would prefer the articles here to have a bit more leeway, rather than being so strict, in their descriptions so it would be more easily understandable.--Officer781 (talk) 00:27, 3 November 2013 (UTC)
No every electron-combination we as smart people can envision are actually important resonance structures (or even existing ones (or even "resonance structures" at all)). I don't see any orbital overlap across the ring (an inside para/para combination) that would give us a Dewar-like form. The geometric change from planar hexagon to two-squares hinged at a new sigma bond is waaaaay more of an actual chemical change than just alternate electron configuration. DMacks (talk) 01:21, 3 November 2013 (UTC)
I agree with DMacks. The Dewar structure is qualitatively different from the Kekulé, and seems stranger to nonexpert readers because of the long bond, so that it is reasonable to omit it from a simple discussion of resonance in benzene. For SF6 on the other hand, the reader can easily count 15 four-bond structures which are all similar and equally simple, so it is mystifying to have a diagram which claims there are only 12. I would prefer to have a diagram which said (x15), but I compromised by leaving the diagram of Officer 781 with the (x12) and adding an explanatory note. I will now restore this note - please do not remove it again. Dirac66 (talk) 01:58, 3 November 2013 (UTC)

Unpaired electrons in structures[edit]

The structural drawings for both PF5 and SF6 now show unpaired electrons (on P and F, though not on S), for which I believe there is no experimental evidence in these molecules. All non-hypervalent published structures which I have ever seen follow the octet rule and show ionic structures - PF4+ F- and SF42+ (F-)2. Dirac66 (talk) 14:36, 4 October 2013 (UTC)

There are unpaired electrons?---Officer781 (talk) 00:29, 3 November 2013 (UTC)
Hmm. I bought new glasses last week and can now see that what I thought were unpaired electrons are actually tiny + signs on P and tiny - signs on F. Perhaps you can enlarge these signs. Dirac66 (talk) 02:04, 3 November 2013 (UTC)
Done. I'll enlarge the signs for the images at the orbital hybridisation article after lunch. Are they better?--Officer781 (talk) 04:25, 8 April 2015 (UTC)
Yes, thank you. Dirac66 (talk) 18:10, 8 April 2015 (UTC)

Changes to diagrams[edit]

@Officer781: Today you changed the diagrams and their captions in the section Ab initio calculations with the edit comment I have no idea how this error could have been overlooked for years. I think the answer is that the errors are not obvious, at least to me. Could you explain here on the talk page what exactly was wrong and what you have changed? Dirac66 (talk) 16:45, 7 April 2015 (UTC)
The two images were duplicated but the captions were different. In other words, one of the images was phosphorus standing in for silicon and another was vice versa.--Officer781 (talk) 03:56, 8 April 2015 (UTC)
OK. I have enlarged these images somewhat for legibility. Dirac66 (talk) 18:10, 8 April 2015 (UTC)

2-Norbornyl cation[edit]

@Officer781: I see you decided today to delete 2-norbornyl cation from this article, and then decided to put it back. I have doubts also about its inclusion, especially since at 2-Norbornyl cation#Hypovalency: The Non-Classical Picture it is described as hypovalent which means having a less than normal valence (as opposed to hyper which means more than). The structure is rather confusing to me and probably to other readers. Perhaps more explanation is needed — could you specify which carbon (C1—H, C2—H or C6—H2) is hypervalent, and which are the five bonds to that atom? Dirac66 (talk) 19:55, 8 May 2015 (UTC)
Carbon number 6 is coordinated to five atoms, but it is not "pentavalent" in the sense that there are 5 pairs of electrons (because it has four. a C-C bond, two C-H bonds and one 3c-2e linking three carbon atoms.). It's more like the methanium ion. Strictly it is not hypervalent. I didn't see the conflation of valency with atomic coordination until I re-examined it today. I guess I will remove the cation unless someone raises concerns about removing it.--Officer781 (talk) 02:46, 9 May 2015 (UTC)
Thanks for clarifying which carbon was meant. No, carbon never has an expanded octet so it should not be described as hypervalent or pentavalent. If someone else does insist that the 2-norbornyl cation be included in this hypervalent article, I would request a source describing its C6 as hypervalent or pentavalent. Dirac66 (talk) 20:39, 9 May 2015 (UTC)

CF5[edit]

How come there's nothing on Carbon Pentafluoride? I would love to add a page, but all I can say for sure is that the Carbon atom is bonded to five Fluorine atoms because of orbital hybridization. I couldn't even find a single page about CF5 on Google. 32ieww (talk) 04:54, 23 November 2016 (UTC) 32ieww (talk) 04:54, 23 November 2016 (UTC)

There is nothing on Google simply because CF5 is not a stable molecule and does not exist. Therefore there is no reason to include it in a Wikipedia article. Dirac66 (talk) 16:56, 23 November 2016 (UTC)

I heard about it on Outrageous Acts Of Science and saw footage of someone setting it on fire. If so, how could it not exist? 03:43, 9 December 2016 (UTC)03:43, 9 December 2016 (UTC)03:43, 9 December 2016 (UTC)03:43, 9 December 2016 (UTC) 32ieww (talk) 03:43, 9 December 2016 (UTC)

Without having seen it myself, I have no idea what they actually did and said, or how well/vaguely/poorly they explained it. But Dirac66 is right, that compound doesn't exist as such, which is the reason there are so few google hits (and likewise none of actually ever having made it in scientific literature that I checked). DMacks (talk) 05:04, 9 December 2016 (UTC)