Talk:Woodward–Hoffmann rules

message: 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 Wikipedia: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)
replies: text: 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)
thread_title: Footnotes and page numbers

message: 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)
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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)
thread_title:  suprafacial & antarafacial 

message: 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)
thread_title: Regarding '''In a thermal pericyclic rxn the total number of (4q + 2)<sub>s</sub> and (4r)<sub>a</sub> components must be odd.'''

message: 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)
thread_title: To V8rik 

message: 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)
thread_title: Again to V8rik, and Also to Koala Paw

message: 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.
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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)
thread_title:  electrocyclic rxn's 

message: The pi* and sigma_A* look like they're accidentally switched
[4+2] cycloaddition correlation diagram Frisk17 (talk) 03:02, 20 July 2022 (UTC)
thread_title:  Correlation diagram of [4+2] cycloaddition mislabeling