Talk:Heterocumulene

Common heterocumulenes

At least for inorganic chemists, "heterocumulene" is used more loosely than implied in this article.

Of the top of my head, the following molecular, inorganic heterocumulenes are routinely encountered and indeed are important industrial compounds: carbon dioxide and carbon disulfide. More exotic compounds are carbon subsulfide, sulfur diimide, and carbon diselenide. Ionic inorganic heterocumulenes are more numerous, including thiocyanate, cyanate, and their isomers isothiocyanate and isocyanate. The following molecular, organic heterocumulenes are also routinely encountered and indeed are commercially important compounds: ketene, various isocyanates. Slightly more specialized is dicyclohexylcarbodiimide. We also need to be attentive to the term stable. Most of the stuff in the interstellar medium is ultra-dilute and do not survive bimolecular processes, which would induce condensation. But that is an inorganic perspective. Lots of reviews (WP:SECONDARY) on their coordination chemistry. S/Se, C, N, and O are the usual ingredient elements because they follow the double bond rule.--Smokefoot (talk) 04:57, 31 July 2017 (UTC)

Things like N-Sulfinylaniline and Sulfur diimide are not even straight/linear, and containing a ring is a bit strange to call it a heterocumulene. I suppose I can accept that it does not have to contain carbon. I will add the ones that definitely look straight, including the ions. But I will need to see a different definition before adding things with more than one hydrogen atom on one end! A big section on coordination chemistry sounds good to have. So do these loose definitions say consecutive double bonds with a non-carbon make a heterocumulene? Graeme Bartlett (talk) 12:16, 31 July 2017 (UTC)

Chemists are probably not so attentive to the rules but we write a lot of papers. It is pleasing to see this area includes the otherwise arcane astro perspective. The operative definition in the chemistry world hinges on the connectivity X=Y=Z. When I get settled in a day, I will dig up some reviews. In my literature database, about 8 titles pop up with heterocumulene in title/abstract, focused on SO2, CS2, CO2, COS, sulfinyl this and that. --Smokefoot (talk) 13:50, 31 July 2017 (UTC)

Here are some reviews from SciFinder search of "heterocumulene". I selected either highly cited ones or ones that through their titles show how chemists view this type of molecule. The doi's are at the end of the refs.

• Szabo, W. A., "Chlorosulfonyl isocyanate. Silver anniversary of a lively heterocumulene", Aldrichimica Acta 1977, 10, 23-29. no available
• L'Abbe, G., "Six-membered heterocyclic isocyanates and isothiocyanates: synthesis and reactions", Synthesis 1987, 525-531. 10.1055/s-1987-27994. 1st line from abstract "The title compds. constitute a unique class of heterocumulenes because of their high reactivity and tendency to di-, tri- or polymerize. "
• Molina, P.; Vilaplana, M. J., "Iminophosphoranes: useful building blocks for the preparation of nitrogen-containing heterocycles", Synthesis 1994, 1197-1218. 10.1055/s-1994-25672. 1st line of abstract "A review with 135 refs.  The almost centenarian reaction of iminophosphoranes with carbonyl or heterocumulene compds. (aza-Wittig reaction) is presented"
• Wentrup, C.; Fulloon, B. E.; Moloney, D. W. J.; Bibas, H.; Wong, M. W., "Novel heterocumulene (RN=C=C=C=X) and ketene rearrangements", Pure Appl. Chem. 1996, 68, 891-894. 10.1351/pac199668040891
• Louie, J., "Transition metal-catalyzed reactions of carbon dioxide and other heterocumulenes", Curr. Org. Chem. 2005, 9, 605-623. 10.2174/1385272053765033
• Madelaine, C.; Valerio, V.; Maulide, N., "Revisiting keteniminium salts: More than the nitrogen analogs of ketenes", Chem. - Asian J. 2011, 6, 2224-2239. 10.1002/asia.201100108. 1st line of abstract "A review.  Keteniminium salts are powerful electrophilic heterocumulene reagents well-known for their selectivity and stereocontrol in [2+2] cycloaddns."

I am still unsure if linearity of the unsaturated core is part of any definition, maybe it is. Also my claim that ions like OCN- are heterocumulenes could be dubious. --Smokefoot (talk) 02:45, 1 August 2017 (UTC)

@Smokefoot: What is the reason why (some?) inorganic chemists wish to ignore the IUPAC standard? Loose use does not mean it is correct use. Have they challenged IUPAC to change the meaning of the term? Egon Willighagen (talk) 07:14, 12 May 2018 (UTC)

@Egon Willighagen: 1) Most of us consider IUPAC, but only as an advisory role. 2) If the goal of writing is to communicate, common usage is often superior to IUPAC, 3) Adherence to IUPAC often anticorrelates with chemical knowledge (i.e. people really really interested in nomenclature are often not very knowledgeable about chemistry. --Smokefoot (talk) 14:36, 12 May 2018 (UTC)

1) What about my second question: did they challenge IUPAC to change the meaning? 2) what is common sense about thinking of (hetero)cumulenes subclass of (hetero)allenes? 3) Would love to read (your) research about that anticorrelation, sounds like a  :) --Egon Willighagen (talk) 07:28, 13 May 2018 (UTC)

IUPAC Gold Book definition

We have to be careful to distinguish common usage from actual definition, or at least state when common usage goes beyond or contradicts that, or when different fields of study have different meanings. For example, Gold Book says a cumulene (parent class) has to have at least three double-bonds and can have other attached groups on the terminal atoms, and for heterocumulenes specifically "not CH2=C=O, ketene, nor O=C=O, carbon dioxide, which are heteroallenes." DMacks (talk) 09:50, 22 August 2017 (UTC)

The Gold Book seems a good starting point to providing a sourced definition. Previously the intro with the definition contained zero references, even though the rest of the article contained ten references. So I have now inserted the IUPAC definition at the start of the article, and also included the definition of cumulene which is necessary to understanding the IUPAC definition of heterocumulene.

If other definitions are widely used, either explicitly or implicitly by examples, they can be added also provided they are supported by sources as per usual Wikipedia policy. If other sourced definitions are not added, then we should eventually delete all the examples with less than three cumulative double bonds. However I will wait for the reaction to my edit before starting to chop out examples unilaterally. Dirac66 (talk) 00:28, 23 August 2017 (UTC)

Sound good to me. My main contribution above was to point out that in some circles, CO2, SO2, diimides are called heterocumulenes, so we might note that usage with a ref.--Smokefoot (talk) 02:22, 23 August 2017 (UTC)

OK, I have added a note that some authors extend the IUPAC definition to the case of only 2 double bonds, with as source a 2011 journal abstract describing HN=C=NH, O=C=O and Ph-N=C=O all as heterocumulenes. So there is no reason to delete examples with 2 double bonds since they do fit this expanded definition. I have however deleted the examples with only 1 double (or triple) bond: CO, CN, etc. Dirac66 (talk) 01:21, 24 August 2017 (UTC)