Talk:Woodward–Hoffmann rules

Footnotes and page numbers
I removed two tags {nofootnote|article} and { pagenumbers | article } because I do not see how they contribute to Wiki. Do not be greedy, Any reference at all in a Wiki article is the best you can hope for in the current chemistry section. We do our best so please be patient. If you feel strongly about inline referencing you can do it yourself and there is no need to place the tag. Also the Scientific_citation_guidelines do not mention page referencing anywhere, so no consensus reached yet Also by now we have so many tags (expert help, please expand bla bla bla) it is possible to remove the actual text from the top of the screen. Do we want that? V8rik 21:15, 5 March 2007 (UTC)
 * Those tags categorize the article in ways that help others improve it. They aren't a badge of shame. Having said that, this article also uses "References" for non-referential footnotes, which should be split out into a separate "Notes" section if not incorporated into the text as parentheticals. EllenCT (talk) 00:05, 15 February 2020 (UTC)

suprafacial & antarafacial
SUPRAfacial & ANTARAfacial are words not to be missed when discussing the Woodward-Hoffmann rules.

all the talk about who takes the credit is nice, for historical records, but so far this article lacks a lot of "meat". more than that, it's outright confusing to find a big "controversy" heading in the contents listed right after "electrocyclic reactions"........... this really isn't good...

it is misleading, in many ways. as far as the RULES are concerned: THERE IS NO CONTROVERSY. THEY MUST BE OBEYED, if the rxn is TRULY pericyclic.

if the rules are "violated" the rxn is not pericyclic:

(not concerted but rather stepwise and ionic, as are some rxn which look like [2+2]'s but are NOT: e.g. the rxn between an enamine and a vinyl ketone is NOT a Diels-Alder [4+2], it's stepwise and ionic, or between an enamine and methyl acrylate is NOT a [2+2] but: stepwise and ionic)

it may be pericyclic, even though it SEEMS to disobey the rules:

"other" orbitals may be involved etc... see (perpendicular pi) orbitals of ketenes and allenes or the vinyl cation (in the Smirnov Zamkov rxn), the latter three cases are pericyclic and hence must obey the rules.


 * In a thermal pericyclic rxn the total number of (4q + 2)s and (4r)a components must be odd.

that's it in a buttshell. should be the first and most important sentence of the entire article. the rest is comment and explanation. "dessert", if you like.

pericyclic rxn's are three: cycloadd, sigmatropic, and electrocyclic.

so why does electrocyclic feature as the only one in "contents"??

how about covering the basics first, e.g. some nice ORBITAL plots showing what this is all about... these are basics and essential!

--Koala Paw (talk) 13:09, 18 March 2008 (UTC)

Regarding In a thermal pericyclic rxn the total number of (4q + 2)s and (4r)a components must be odd.
The requirement of(4q + 2)s and (4r)a being odd was published only in 1969 long after the original Woodward-Hoffmann 1965 papers and after the 1966 Zimmerman Möbius-Hückel ones. BUT this is equivalent to the Zimmerman M-H requirement that for 4N electrons one needs a Möbius orbital array. Each W-H (4r)a component introduces one plus-minus node and with an odd number of these one has 4N electrons for that Möbius system. With an even number of these, the number of plus-minus overlaps is even and one has a Hückel system for the 4N electrons and that is "forbidden".

In brief, this is a sneaky way of paraphrasing the Möbius-Hückel requirements and making it look like something new. Hez (talk) 18:45, 13 July 2010 (UTC)


 * Hi Howard, if I look at the original 1965 article it states rules for (4q + 2)s and (4r)a compounds. The article does not mention odd/even effects and also the current Woodward–Hoffmann rules article does not mention odd or even V8rik (talk) 21:01, 16 July 2010 (UTC)

To V8rik
Hi, I don't know if I responded to this earlier, but the "hidden" effect is the (4r)a since each antisymmetric component provides an odd plus-minus overlap.I hope this gets to you. I put it here since it refers to your question.

We don't seem to talk much these days. I've been busy with the Pacifichem symposium I've organized.


 * You have picked a nice location: Hawaii! V8rik (talk) 22:07, 12 December 2010

Hez (talk) 23:33, 9 December 2010 (UTC)

Again to V8rik, and Also to Koala Paw
I don't see where I have responded to questions (above) full or given references to what I had said.

Thus, V8rik, you are correct the Woodward and Hoffmann in the 1965 papers don't discuss "parity" There is no mention of "odd" (or versus "even"). There is use of rules for (4q + 2)s and (4r)a not in relation to "odd" or "even". It is only in their 1969 Angewandte Chemie paper and in the 1970 Verlag Chemie - Academic Press booklet that the "Generalized" rules are given.

The references are: Woodward, R.B; Hoffmann, R., Conservation of Orbital Symmetry Angew. Chem. 1969, 81, 781-932. Woodward, R. B.; Hoffmann, R., “Conservation of Orbital Symmetry” – Verlag Chemie, Academic Press, 1970 Pg. 169

In my 2006 Pure and Applied Chemistry article I do note the way in which this "Generalized" concept is introduced and this is just a repeat of the Moebius-Hueckel concept. This last reference is:

Howard E. Zimmerman, “Five decades of mechanistic and exploratory organic photochemistry”, Pure Appl. Chem., 2006, 78, 2193–2203.

And curiously there is no reference to Moebius-Hueckel in the Woodward-Hoffmann articles.

I hope this extra stuff helps. I don't quite know what to do with this in Wikipedia. But take a look and see what your impression is.

Hez (talk) 17:47, 20 May 2011 (UTC)

(UTC)

electrocyclic rxn's
all electrocyclic rxn's are WH allowed.

both thermally and photochemically.

whether the ORBITALs perform a CON or DIS rotation is PREDICTED / DICTATED by the WH rules.

minor CAR BAT:

although the above is true in principle, STERIC requirements may, in some rare instances, make one or both modes of rotation IMPOSSIBLE (e.g. cyclooctadienyl anion only undergoes thermal, disrotary cyclization; the photochemical CON mode is thwarted by sterics... π6s, hence WH -> DIS for thermal rxn).

--Koala Paw (talk) 13:38, 18 March 2008 (UTC)

Dewar mispelled as "Dewer"
For Michael J.S. Dewar. There are too many occurrences for me to correct

Corey claim ref
Do we really need the Corey claim as cite number one? This topic is handled in the controversy section at the bottom of the article. V8rik (talk) 17:47, 21 February 2017 (UTC)


 * Good point. I think the first 2 sentences of the current note 1 concerning Corey and Hoffmann's response can just be deleted from the intro, as they are fully dealt with in the Controversy section where it belongs. However it is less clear what to do with the third sentence concerning Havinga and Oosterhoff. Is this claim is also opposed by Hoffmann? If so, perhaps it should be added to the Controversy section as well. Dirac66 (talk) 01:20, 22 February 2017 (UTC)
 * it is certainly worth investigating V8rik (talk) 17:04, 22 February 2017 (UTC)


 * I agree. E.J. Corey's claim has been deemphasized in note 1, which has been rewritten as "Although the principle of orbital symmetry conservation was first articulated by R. B. Woodward and R. Hoffmann, E. Havinga had previously noted that tachysterol underwent electrocyclic ring closing in a conrotatory or disrotatory manner depending on activation mode (photochemical or thermal, respectively) and attributed an orbital symmetry explanation for this phenomenon to L. J. Oosterhoff (Tetrahedron Lett. 1961, 16, 146). Additionally, E. J. Corey has claimed priority in proposing the key insight (see 'Controversy' section below)."
 * R. Hoffmann credits the Havinga-Oosterhoff work as a "forerunner" to the general idea, but claims credit for proposing the W-H rules as a general explanation for the outcome of pericyclic reactions.
 * Does anyone have the earliest reference to the Dewar-Zimmerman approach? Arguably, their proposal is just as general (it turns out to be formally equivalent to the W-H rules), so potentially, they also have a claim to discovery.
 * Alsosaid1987 (talk) 05:01, 6 August 2017 (UTC)

Correlation diagram of [4+2] cycloaddition mislabeling
The pi* and sigma_A* look like they're accidentally switched

Frisk17 (talk) 03:02, 20 July 2022 (UTC)