User talk:Dirac66

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User talk:Dirac66/Archive 1 (2006-2010)

User talk:Dirac66/Archive 2 (2011-2012)

User talk:Dirac66/Archive 3 (2013-2014)

Symmetry text[edit]

Deferring to your probably better instincts, I admit to being irked by the recent insertion by an author pitching his textbook on symmetry into Molecular symmetry. It seems to be an unfortunate precedent. --Smokefoot (talk) 20:01, 31 December 2014 (UTC)

I have now followed the hint given by Bunkerpr's edit summary and looked at the original publication on permutation-inversion groups by H.C. Longuet-Higgins, Molec. Phys. 6, 445 (1963) The symmetry groups of non-rigid molecules [on-line at http://dx.doi.org/10.1080/00268970110088695, with a new volume number and year! it was actually written in 1963.] The key word in the title is non-rigid - Longuet-Higgins proposed his method to classify spectroscopic levels of molecules moving between equivalent multiple geometries, such as inversion of NH3 or hindered rotation of C2H6. For single geometries there is no advantage over the usual method, and no reason to refer to this method as true symmetry.
So since this is an extension of the usual simpler method to a more general case, I propose (soon) to replace the confusing sentence in the opening paragraph by a section at the end named perhaps Extension to non-rigid molecules, and explain the objectives of this unusual method. My source would be Longuet-Higgins' article, though Bunker's book could serve as an additional reference as long as the original source is given first. Dirac66 (talk) 00:38, 3 January 2015 (UTC)

Electrovalency[edit]

While browsing under categories, came across this article today: Electrovalency. Seems like a synonym for ionic (electrovalent bond=ionic bond. electrovalent charge=ionic charge). The article is also mostly an orphan. Any ideas what to do with it? Probably merge or create sections under existing articles that link to it?--Officer781 (talk) 02:38, 6 April 2015 (UTC)

Yes, electrovalency is just an old-fashioned synonym for ionic bonding. So I would suggest merging it into the Ionic bonding article: transfer any content which is not already in Ionic bonding, and mention somewhere in the intro that electrovalency is an alternate name. Dirac66 (talk) 10:58, 6 April 2015 (UTC)
Done. Thanks!--Officer781 (talk) 11:27, 6 April 2015 (UTC)

Carbenes and free radicals[edit]

Is carbene a free radical? I see that the list at octet rule has carbenes separated from free radicals. I'm confused about the definition of free radical. Is free radical a species with an open valence shell? Or is it one with unpaired electrons (which then also includes those with closed valence shells like nitric oxide)? Or a confused mix of both? I don't think the article on wikipedia helps much either (since it gives the definition unpaired or (ie, ∪) open shell).--Officer781 (talk) 02:27, 9 April 2015 (UTC)

Hm. I learned that a free radical is a species with unpaired electrons. A triplet carbene has two unpaired electrons so is a diradical, but a singlet carbene has no unpaired electrons so is not a radical at all.
However I am not 100% certain that I am correct and up-to-date, so it would be wise to check some books. And remember that the definition has changed with time - 100 years ago a radical meant an unstable fragment of a molecule, no matter how many electrons it had. Dirac66 (talk) 02:42, 9 April 2015 (UTC)
The IUPAC definition seems to omit the open shell requirement (it's simply just unpaired electrons). So I've updated the free radical article accordingly and removed that as a category in the octet rule page (some radicals fulfill octet, some don't).--Officer781 (talk) 03:08, 9 April 2015 (UTC)

Valence shell definition[edit]

It is said in the octet rule article (and I'm sure some other Wikipedia articles) that a transition metal's d orbitals are counted in the valence shell. What exactly is the definition of valence shell? Because the article electron shell defines valence shell as the outermost shell (ie the highest principal quantum number) and that is different from valence electrons. Certain usages outside Wikipedia seem to imply valence shell is simply the orbital levels that encompass valence electrons. So we have two conflicting definitions here.--Officer781 (talk) 05:40, 11 April 2015 (UTC)

Yes, the chemical literature is sometimes contradictory which makes it difficult to write consistent Wikipedia articles. The original definition was the shell with the highest principal quantum number, as per Bohr, Sommerfeld, Lewis and Langmuir etc. But chemists often disagree - certainly in VSEPR the valence shell for Ti includes all the valence electrons, both 4s and 3d. So I think Wikipedia should adopt a neutral point of view (WP:NPOV) and point out explicitly that both definitions are used, preferably with sources for each definition. Dirac66 (talk) 15:42, 11 April 2015 (UTC)

New article[edit]

I've made a new article Sigma-pi separation to cover an area I thought Wikipedia did not sufficiently expound on. Could you take a look and help improve on it? Thank you.--Officer781 (talk) 15:35, 13 April 2015 (UTC)

I think this new article confuses historical and current aspects, which are both dealt with in other articles. In the early days of quantum chemistry (say 1930-1960), computers were very primitive so the quantum chemists made many drastic approximations. Sigma-pi separation was used in the Hückel method for planar organic molecules as a reason to do calculations separately for only the pi orbitals which are perpendicular to the molecular plane. Sigma orbitals in the plane were neglected with the attitude that well, they are just localized bonds which we already understand and the pi orbitals are the objects of interest. It was understood that this approximation is often drastic, but the available computers limited what could be done. This historical aspect of the subject is already mentioned at Hückel method.
The current aspect of the article concerns the best simple description of multiple bonds, lone pairs, etc. We can of course now include all the orbitals in the computations, so the question is just whether simple explanations should use sigma and pi orbitals, or (s-p) hybrid orbitals. This is not really concerned with sigma-pi separation, just with whether or not to describe the molecule using sigma and pi orbitals. And as already pointed out in other articles which you have edited, the two descriptions are equivalent for closed-shell ground states but not for ionized or excited states.
So my advice would be to replace the article by a redirect to Hückel method for the historical aspects, and to cover the current aspects in other articles on bonding, hybridization, etc. Dirac66 (talk) 15:00, 14 April 2015 (UTC)
Actually, the section on double and triple bonds were initially covered in bent bonds and I felt an extended version covering lone pairs was necessary. There was also a description of mixing sigma and pi at localized molecular orbitals that could also do a description so I thought of creating this article. I've renamed it "sigma-pi model" and redirected the old name to Huckel method. I'll go ask some other users and get a consensus.--Officer781 (talk) 02:39, 15 April 2015 (UTC)
Yes, I agree that Sigma-pi model is better than Sigma-pi separation. Dirac66 (talk) 20:14, 15 April 2015 (UTC)

Transfer material from chemical bond to covalent bond[edit]

I feel that the article as it is currently is too extensive for a general article in my opinion. Sections such as "Valence bond theory", "Comparison of valence bond and molecular orbital theory" and "Bonds in chemical formulas" could really do better under the covalent bond page. Should a content transfer be done? Moreover, the wikimedia tool specifying the hit rate shows that covalent bond is higher on the list. Those guys would be missing out on important info.--Officer781 (talk) 15:29, 18 April 2015 (UTC)

Disambiguation link notification for April 26[edit]

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Magnetic moments[edit]

Do we have a page with a table of magnetic moments vs electron count? And then perhaps discussion of corrections for spin-orbit coupling? Part of the problem (at least for me) is that the magnetism articles are heavy on the physics.--Smokefoot (talk) 23:59, 30 April 2015 (UTC)

I have just found this subject at Magnetochemistry#Theoretical calculation for complexes of metal ions. Since observed values are considered as well as, I suggest changing the section title to Magnetochemistry#Complexes of transition metal ions. Also we could make the article (or article section) easier to find by adding See also links to related articles, including Magnetic moment, Coordination complex and d-electron count. Dirac66 (talk) 01:33, 1 May 2015 (UTC)

Delocalized electrons and aromatic ring current[edit]

I've recently changed the delocalized electron article to a disambiguation as there are multiple meanings of the term which I feel mean different things in different fields that are often confused (it can be delocalized but static, which means it cannot conduct electricity (unlike the term used for metals and graphite). Delocalization ie resonance is different from delocalized molecular orbitals, also for example as there are delocalized molecular orbitals where there is no resonance.). The old article did have a link. It mentions aromatic ring current, whereby on reaching the page I am told that it is because of the delocalized pi electrons. But these electrons are in discrete energy levels unlike graphite (which has a half filled pi conduction band consisting of a fully filled bonding band and an empty antibonding band with no band gap). This is not an area I'm knowledgeable in but I highly doubt the absurdly simple explanation on that page conflating the chemical definition of delocalization with the conduction definition used in physics (ie mobile electrons). It almost begs to ask the question why non-aromatic ring systems don't create a ring current as they can be depicted by delocalized molecular orbitals.--Officer781 (talk) 10:55, 9 May 2015 (UTC)

You may have confused two types of electric current. Solid-state electronic conduction of electricity over macroscopic distances does normally involve MO's delocalized over macroscopic distances and partly filled conduction bands. However the article on aromatic ring current concerns current flowing around a single molecule such as benzene under the influence of a strong magnetic field in an NMR experiment. This current involves (pi) electrons in the usual benzene ring molecular orbitals and does not require a continuous energy band. Of course it cannot be detected with an ammeter as it is confined to a single molecule, but it is observable by its influence on the NMR chemical shift of the C or H nuclei. See Chemical shift#Factors causing chemical shifts.
Re the absurdly simple explanation, please copy the dubious sentences here so I will know what you are referring to.
And re non-aromatic ring systems: For a ring current, the electrons do have to be mobile within the molecule. This is not true in a ring with localized bonds such as cyclohexane. Dirac66 (talk) 22:49, 9 May 2015 (UTC)
So mobility of electrons does not have to do with continuous bands? Okay that clears it up. Thanks! The absurdly simple argument now holds, I was mixing it up with the other meaning of delocalization (ie the bonding meaning not the mobile meaning).--Officer781 (talk) 02:47, 10 May 2015 (UTC)

July 2015[edit]

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Boric acid[edit]

I have returned very briefly. Greenwood does describe boric acid as strong acid in its dissolution in anh. sulfuric. The formation of tetra(hydrogen sulfato) boric acid is described in Superacid Chemistry By George A. Olah, G. K. Surya Prakash, Jean Sommer, Arpad Molnar,and the dissolution in anh. sulfuric has apparently a measurable H0 of -13.6. NNG may well have missed out the word "Lewis" in his book as I believe he favored the Lewis acid model for the behavior of B(OH)3 rather than Bronsted (-OH- abstraction). Anyway in the absence of any mechanistic evidence for the reaction pathway that I could find I have removed the debatable acid/base description. Regards. Axiosaurus (talk) 15:25, 3 August 2015 (UTC)

OK, thanks. I agree that just giving the equation without the acid/base description seems best here. It is more complicated than either a simple acid or a simple base. Dirac66 (talk) 18:06, 3 August 2015 (UTC)

Singlet oxygen[edit]

Could you please take a look at Talk:Singlet oxygen? Specifically the new edit that indicates that through some mechanism (that I am not smart enough to understand) singlet oxygen is not diamagnetic. --Smokefoot (talk) 00:24, 13 August 2015 (UTC)

I think the 2012 edit by 195.126.85.201 had the correct explanation, even if the references given turned out to be irrelevant. In chemistry there are two types of electronic angular momentum which can interact with a magnetic field - orbital and spin, as in the quantum numbers ml and ms for the H atom. For O2(1Δg), the singlet indicates that the net spin is zero, but the Δ means that the orbital angular momentum ML (sum of ml for 2 electrons) = 2. The diagram in the article for the 1Δg may be helpful: the electron configuration is σs2 σs*2 σp2 π4 π*2. There are two π* orbitals, one corresponding to orbital motion in each direction. The two electrons shown as red arrows are both in the same orbital with opposite spins, so they both have the same orbital angular momentum and the total is nonzero, and they can interact with a magnetic field.
This is written quickly with no source-checking. I will try to find a better source before commenting on the article talk page. Dirac66 (talk) 01:12, 13 August 2015 (UTC)
Thanks very much. The tip-off is the Δ ground state arising from the degeracy of the π*. So the EPR transition (selection rule being ΔMS = 1) is to the state described still by ML = 2 but with MS = 0? --Smokefoot (talk) 13:09, 13 August 2015 (UTC)
I think the general selection rule is ΔMJ = ±1, where J = L + S (vector sum), or for a linear molecule J = Λ + S where Λ is the component of L around the molecular axis. For most radicals of interest L (or Λ) = 0 so J = S and ΔMS = ±1, and in that case EPR is also known as ESR. But for singlet delta oxygen, S = 0 so J = Λ = 2 and the selection rule is ΔML = ±1. Dirac66 (talk) 13:35, 13 August 2015 (UTC)
And note also that there are other molecules for which both L and S are non-zero. See for example Magnetochemistry#Complexes of transition metal ions. Dirac66 (talk) 15:06, 13 August 2015 (UTC)
I cant think of any long-lived complexes akin electronically to singlet O2, anyway Jahn Teller would kick in, it seems. One aspect that I learned from your explanation is that PhNO (nitrosobenzene) is an imperfect model for singlet oxygen, despite some claims otherwise, because its noncylindrical geometry lifts the degeneracy of the pi and pi star. Again many thanks, also about the more general EPR selection rules. On that note I will digress by suggestion that it would be nice idea to have a SpecBox (akin to a ChemBox) for spectroscopic techniques wherein we would state selection rules, energies, time-scales. --Smokefoot (talk) 22:53, 13 August 2015 (UTC)
Specbox is an excellent idea. We could also add type of excitation and type of system studied. And wavelength and frequency even though these are equivalent to energy. Dirac66 (talk) 23:28, 13 August 2015 (UTC)

Please have a look[edit]

I have a longstanding stalker, someone who reverts me almost in real time when I am making chem edits. It is purely personal, insofar as other chem editors routinely see and read the same text, and leave it. It dates back to me editing this editor's "owned" steroids article. Then he followed me to the natural products article, and has since repeatedly followed me, real time when he is on, or same day, to many, many articles that I sit when I log in. I have repeatedly had to drop editing at articles, because of his following me about.

I am not asking you to get involved in the personal issue. But his latest revert of my work came as I was trying to develop the ledes of both the triplet and singlet articles in parallel, before leaving it off to someone such as yourself to continue with. (I am an OChem and early preclinical drug discovery prof and pharma worker, and not a PChem/IOChem expert.)

I would ask you to look at the edits this editor made to the lede at the singlet oxygen article, in particular, the large redaction of material. I would also have you compare the ledes of the triplet oxygen and singlet oxygen articles to see what I was doing, before he followed me to there and removed the developing parallel structure between the articles (by removing and changing the lede of the singlet article).

Here are links: [1] and [2] (note parallel language), and [3] (note that editor's change to paragraph opening, which paralleled the triplet article, and the removal of the entire introductory paragraph). That latter paragraph was intended as temporary, so that others could move material into the main body, as the Edit summaries and Talk section indicates. (But, it was not intended for part-and-parcel elimination.)

Three closing notes -- (i) I added another citation to your paramagnetic discussion at the singlet oxygen talk page. (ii) I came today to edit the lede in question, in particular to remove citations, which I have since transferred to the Structure section (so they do not have to be repeated in the lede). Still, the Structure section is weak, and needs expert attention from you or a colleague. (iii) I am signing this from URL to prevent the editor from stalking me here as well. I can be found at User:Leprof_7272. Le Prof 71.201.62.200 (talk) 17:17, 18 August 2015 (UTC)

I have now looked at this talk page which has become rather heated of late. Perhaps all involved should try to restore calm - no one owns a Wikipedia article and sometimes we have to negotiate compromises. In this case I think the other editor's 3 (only) recent edits do not seem so terrible. I am not so sure why there must be parallel articles on triplet and singlet oxygen. Since triplet is the ground state, I would have expected the triplet nature to be just one section of a longer article on dioxygen, including other topics such as respiration, liquid oxygen, etc. etc. Singlet on the other hand is an excited state of great interest (plus one higher excited state of less interest), so I would expect that the Singlet oxygen article contain both the nature of the excited state(s) compared with the ground state, and the various applications. That would be my viewpoint if I were starting a new article, but don't worry - I will not try to impose still another major restructuring of this article. Eventually I would like to insert an answer to the question of why the 1Δ state is paramagnetic. Dirac66 (talk) 23:58, 18 August 2015 (UTC)