Talk:Allenes

Image

The image should have a dot in the middle. At the moment it looks like ethene, not allene. 195.50.199.82 (talk) 20:35, 5 January 2011 (UTC)

Now the image appears to be bent? The article states a bond angle of 180 degrees, so this should be fixed... --Pyrochem (talk) 23:56, 14 November 2011 (UTC)

Allenic chain family

I find mention of an "allenic chain family HC_(2n)N"[1] in reference to the detection of interstellar molecules. That doesn't seem to fit the definition in this article, so I'm wondering how they are related. Any ideas? Thank you.—RJH (talk) 19:09, 22 September 2008 (UTC)

Doesn't seem to make sense. Without the HC_2nN bit, I would have thought they meant cumulenes.

Ben (talk) 19:26, 22 September 2008 (UTC)

My guess is that RJH is referring to cyano-acetylenes - N≡C-(C≡C)_n-H. User:Stone's the one for this question.--Smokefoot (talk) 23:33, 22 September 2008 (UTC)

Seems it's the cyanoethynylmethylene radical.

Ben (talk) 00:04, 23 September 2008 (UTC)

Symmetry

The image displaying the C₂ axis needs to display the second C₂ axis? 111.69.253.197 (talk) 06:07, 22 October 2010 (UTC)Josh

The second axis is perpendicular to the screen and would therefore appear only as a point. -- Ed (Edgar181) 13:37, 22 October 2010 (UTC)

That's right, but there are actually 3 C2 axes in total. It's correct that one of them goes into the page. Of the remaining two however, only one is shown. The other is similar in that it is another 'propeller' axis. In the image it should appear in the plane of the screen, at 90 degrees to the propeller axis already shown. If the molecule had only two axes, it would not belong to the D2d point group! 111.69.244.197 (talk) 23:18, 28 October 2010 (UTC)Josh

Yes, there is one at 90 degrees to what we have now. I'll fix the image... unless someone beats me to it first. --Rifleman 82 (talk) 04:22, 29 October 2010 (UTC)

I have produced the image we need but am unable to upload I haven't made enough edits on wikipedia (10 necessary) - if someone can, let me know your email address, and I can pass on the picture. — Preceding unsigned comment added by 139.80.123.40 (talk) 01:49, 30 May 2012 (UTC)

Pentadiene

Chemical and spectral properties

I believe that the two double bonds in 1,4-pentadiene are conjugated, not isolated. Simon de Danser (talk) 07:01, 26 October 2020 (UTC)

That is not correct. In 1,4-pentadiene, the alkenes are C1–C2 and C4–C5 (CH₂=CH–CH₂–CH=CH₂). That central CH₂ (carbon #2) prevents the two alkenes from being conjugated with each other. DMacks (talk) 09:18, 26 October 2020 (UTC)

Thanks, my mistake. I mixed up with cyclopenta-1,4-diene.

Simon de Danser (talk) 13:35, 26 October 2020 (UTC)

Perhaps the article should state that the C=C's in allenes are not conjugated.--Smokefoot (talk) 14:46, 26 October 2020 (UTC)

Agreed. DMacks (talk) 21:14, 26 October 2020 (UTC)

This is surely what this sentence meant, and I agree it was poorly written. How about "The two alkene units are not conjugated to each other because the pi bonds are not in the same plane."? That last detail is a key aspect of the Geometry article-section. DMacks (talk) 03:10, 27 October 2020 (UTC)

Bent arrows in allenes chirality

According to Cahn-Ingold-Prtelog rules, bent arrows should be placed between Cl and OH substituents. The directions are correct. 2A01:1DC:1:2:0:0:2:DACA (talk) 13:15, 29 May 2023 (UTC)

An arrow from a 'back' atom to a 'front' atom is not relevant to R/S of allenes. Instead, "it is immaterial from which end it is viewed; the nearer pair of ligands receives the first two positions in the order of preference" (IUPAC, quoted in Axial chirality) so all that matters is going from the front to the back. DMacks (talk) 17:19, 29 May 2023 (UTC)