Talk:Diene

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What's the difference between allenes and cumulated dienes? From the description, it looks like they're the same thing. Anyone know enough chemistry to clear this one up? Grendelkhan 07:52, 2004 Apr 22 (UTC)

Allene is an archaic, non-systematic, name for propadiene that is still allowed by IUPAC, similar to ethylene/ethene. Propadiene (really techinally propa-1,2-diene) is the simplest comulated alkadiene, so it's common name is sometimes used by the entire group of comulated alkadienes, although this should be avoided because of possible ambiguation.

On a different note, this article really should reside at alkadiene, as that's the IUPAC approved name for this class of chemicals, with Diene as a redirect. Gentgeen 10:54, 14 May 2004 (UTC)[reply]

Linoleic acid

Linoleic acid should be removed from the second image. Linoleic acid contains oxigen atoms, hence it doesn't belong to the group of dienes. — Assaiki (talk) 06:08, 21 December 2018 (UTC)[reply]

The article makes several mentions of the broader concept of "diene" as any structure containing two alkene units. Fatty-acids and their biosynthesis are mentioned in § Synthesis of dienes. Most (or at least many) Diels–Alder dienes (§ Cycloadditions) are functionalized with electron-donating groups such as oxygen or nitrogen. And ROMP (§ Metathesis reactions) includes fairly complex non-hydrocarbon molecules that just happen to have two separate alkenes. I adjusted the lede to note that "diene" itself might be a hydrocarbon but it could be a substructure of a more complex (unrestricted) molecule. DMacks (talk) 07:04, 21 December 2018 (UTC)[reply]

(Alka)diene

Shouldn't we rename this article to "Alkadiene" ? IUPAC defines alkadiene as an acyclic branched or unbranched hydrocarbon having two carbon–carbon double bond. On the other hand, diene has a much broader definition, they're simply "Compounds that contain two fixed double bonds". Which means any compound, not just hydrocarbons as the wiki article says. — Assaiki (talk) 21:03, 21 December 2018 (UTC)[reply]

I moved the loose Gold Book external-link to be a ref cited for the definitions. It specifies that the atoms are "usually assumed to be between carbon atoms" and gives "heterodiene" as a more specific subcategory for when they do not. I've never heard (for example) an enone called a "heterodiene", much less a "diene", but a few wikipedia articles do that.

I obviously agree we should use authorititative definitions. Thanks for finding the mixups! I adjusted the lede to match the ref, added a note to § Classes about the "heterodiene" term, and added a WP:REDIRECT from heterodiene. Alkadiene as a redireect here already existed. I think at least our article is now self-consistent? I also obviously agree that we can change what "our article" should actually be about, and what title to use based on refs:)

I do not see "alkadiene" mentioned in the definition and I cannot find that term anywhere in the Gold Book, but it is in the ChEBI ontology[1]. Conversely, Gold Book explicitly defines "cumulene" specifically as a hydrocarbon, so our cumulene article is written that way (as opposed to heterocumulene). Do we have much to say about alkadienes that is specific to the hydrocarbon aspect? On the other hand, as a parent-topic, we can link to the subtopic articles of conjugation (not related to element), allene/cumulene (some terminology differences if hetero), and hetero in general (specific articles for enone, etc.) DMacks (talk) 06:15, 23 December 2018 (UTC)[reply]

Thank you for all the input and fixes in this matter. (I would have done it myself, but English is not my native language.)

Regarding alkadiene: IUPAC Gold Book doesn't have a separate article about it, but discusses the term along with alkenes. The "alkenes" article in the electronic version (2014) of Gold Book on page 59 defines the following:

"Acyclic branched or unbranched hydrocarbons having one carbon–carbon double bond and the general formula C_nH_2n. Acyclic branched or unbranched hydrocarbons having more than one double bond are alkadienes, alkatrienes, etc."

So according to GB, alkadiene is a major subclass of dienes. Should we make a separate wikipedia entry for alkadienes, alkatrienes, etc, or just mention them in the alkenes article, like the Gold Book did?

I also noticed, that the external link to "dienes" in the references section is not working. I tried to fix it, but without success. — Assaiki (talk) 10:47, 23 December 2018 (UTC)[reply]

Sorry about the broken ref...fixed. And thanks for the pointer to that Gold Book entry. Interesting that sometimes the "simple" name can refer to either hydrocarbon or hetero (with separate subclasses) whereas other times the simple name is specifically hydrocarbon. For alkene, they have:

IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "alkenes". doi:10.1351/goldbook.A00224
IUPAC, Compendium of Chemical Terminology, 2nd ed. (the "Gold Book") (1997). Online corrected version: (2006–) "heteroalkenes". doi:10.1351/goldbook.H02790

as separate (not parent/subcat relationship). DMacks (talk) 20:41, 23 December 2018 (UTC)[reply]

~~What do you mean by "simple" name? I thought "alkene" is only used to denote hydrocarbons. I may be wrong, but so far I don't see significant contradictions in Gold Book regarding these definitions.~~

Sorry, I got your meaning since then. And yes, I agree that it's "interesting" :) For example what about coriandrol (linalol)? It's not an alkadiene, since it contains an oxygen atom. It's not a heteroalkene, since the heteroatom is not replacing any double bonded carbon atom. So it seems coriandrol is simply a diene, because it has two double bonds.

By the way, I've made some changes to the article, feel free to correct it if my phrasing is flawed. — Assaiki (talk) 22:55, 24 December 2018 (UTC)[reply]