Talk:Three-center four-electron bond
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This article is or was the subject of a Wiki Education Foundation-supported course assignment. Further details are available on the course page. Student editor(s): Arun sridharan.
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Untitled
[edit]Reads like an advanced chemistry textbook. --Fang Aili 04:47, 12 January 2006 (UTC)
I have moved the { technical } tag to the article, instead of the discussion page. It will be more useful there, since the discussion isn't technical at all.
whats unverifiable
[edit]whats unverifiable about the article? Xcomradex 02:45, 24 July 2006 (UTC)
Should we move this article
[edit]It makes sense (to me) to move/merge this thing with hypervalent molecule. Comments?--Smokefoot 19:10, 28 December 2006 (UTC)
- I think it's better as a separate article, because it is a reasonably self-contained topic that we might want to link to from other articles (for example, contrasting it with the 3c-2e bond). In hypervalent molecule, it would just be a subtopic, so it would not be cleanly linkable (I personally hate links that take me to the middle of a page, and even worse, links that take me to the top of a page that doesn't seem to be about what I expected). Itub 19:33, 28 December 2006 (UTC)
Figure
[edit]Thanks for adding the figure, it looks really nice. I wanted to add one myself, but didn't have time. The only thing I'm not sure is right is the label of the HOMO as "bonding". I've typically seen it as "nonbonding"; for example, in Greenwood. I noticed that you also removed the mention of nonbonding from the main text; is there a strong reason for it? Itub 19:36, 28 December 2006 (UTC)
- Oh gosh, you are correct, I meant NB. --Smokefoot 20:32, 28 December 2006 (UTC)
Scope of article
[edit]I have never understood the term "Three-center four-electron bond" only in the restricted sense of this article as it now exists. I have always seen the pi bonding in -COO- and the allyl anion as being simple example of 3c-4e bonding with hypervalent compounds as an extension. Should the scope of the article be widened? Note also that the examples of XeF2 etc is sometime called "Rundle 3-c bonding". --Bduke 22:46, 11 April 2007 (UTC)
- What you say sounds logical (the MO levels looks the same), but I'm not sure I've seen the term applied to allyl and carboxyl (maybe because those are pi orbitals?). Do you have an example of a reference that calls the bonding in allyl and carboxyl this way? --Itub 05:51, 12 April 2007 (UTC)
- A good question. It does not seem to be as widely used as I thought. It is certainly frequently used by my friend Dick Harcourt with his extended valence structures for electron-rich compounds. Maybe that is why I use it so often. I have seen a reference to ozone as 3c-4e and a few for allyl anion but have not yet looked up the papers. I will discuss the terminology with Dick next week when I see him in Melbourne Uni and also check some books in their library. --Bduke 07:53, 12 April 2007 (UTC)
- What I have been able to find is some sources that use the 3c4e model for hydrogen bonding (and especially for symmetric H-bonds, as in [FHF]-). You are right that sometimes these are called Rundle bonds, or Rundle-Pimentel, as these are the authors to which this model is attributed. The article would benefit from having a history section, I'm sure. --Itub 08:17, 12 April 2007 (UTC)
- A good question. It does not seem to be as widely used as I thought. It is certainly frequently used by my friend Dick Harcourt with his extended valence structures for electron-rich compounds. Maybe that is why I use it so often. I have seen a reference to ozone as 3c-4e and a few for allyl anion but have not yet looked up the papers. I will discuss the terminology with Dick next week when I see him in Melbourne Uni and also check some books in their library. --Bduke 07:53, 12 April 2007 (UTC)
- Now I found a couple of books on google that refer to the bonding in allyl and ozone as "four-electron three-center" (note the reversed order!). [1],[2]. I suspect that what happened was that when the allyl-like systems were first explained, no one thought the bonding was remarkable enough to deserve a name (the octet rule was followed, all the atoms were bound at least with sigma bonds, etc.). But when, a few decades later, a very similar model was applied to hypervalent molecules, which were perceived to be very different, the concept got its own name. Since the bonding in hypervalent molecules tends to be considered "exceptional" (despite the objections of some authors), this term is almost always used in this context. Weinhold and Landis try to be more precise by proposing the term "omega bonds" in their book, but I haven't seen anyone else use it. --Itub 11:42, 12 April 2007 (UTC)
- LOL. I have the first book you found on my shelves and I did not even think to look in it. Plus the table you found is work from the group where I did my D Phil and at the same time. David Hirst was exactly my years in the group. No wonder I use the term! I think the 4e-3c to 3c-4e change is one that has occurred over the years. I'll ask Dick about that too. --Bduke 12:18, 12 April 2007 (UTC)
- Now I found a couple of books on google that refer to the bonding in allyl and ozone as "four-electron three-center" (note the reversed order!). [1],[2]. I suspect that what happened was that when the allyl-like systems were first explained, no one thought the bonding was remarkable enough to deserve a name (the octet rule was followed, all the atoms were bound at least with sigma bonds, etc.). But when, a few decades later, a very similar model was applied to hypervalent molecules, which were perceived to be very different, the concept got its own name. Since the bonding in hypervalent molecules tends to be considered "exceptional" (despite the objections of some authors), this term is almost always used in this context. Weinhold and Landis try to be more precise by proposing the term "omega bonds" in their book, but I haven't seen anyone else use it. --Itub 11:42, 12 April 2007 (UTC)
The article by Ramsden that User:Brichcja recently added to the references is a good example where the bonding in allyl and ozone is called 3c4e, together with the usual hypervalent molecules. Therefore I see no problem with expanding the article to include these other examples. --Itub 12:52, 15 May 2007 (UTC)
"difficulty"?
[edit]I'm not convinced by this statement at the end: "One difficulty with 3-center-4-electron bonding model is the implication that "normal" bonds are localized, 2-center-2-electron bonds. In fact, bonding is highly delocalized." It seems a bit vague. First, who says it is a difficulty? What does it mean by delocalized? It is true that the "normal" molecular orbitals are highly delocalized, but there are alternative representations, such as the natural bond orbitals, that represent the wave function equally well, are more localized and look more like the textbook sigma and pi bonds. I would remove that sentence unless it can be clarified and attributed. --Itub 08:21, 12 April 2007 (UTC)
Overhaul on article material
[edit]No one's really edited this article in seven years; I'm going to give this article a big overhaul, and address the concerns brought up by commenters from back in 2007. I'll update this post periodically with changes I'm making over the next few weeks. --Arun sridharan (talk) 19:16, 9 November 2017 (UTC)