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-- Wikimedia Commons Welcome (talk) 11:25, 7 April 2017 (UTC)

File:Allenes chirality depiction.pngEdit

In your edit to that file, you noted: "Reverted to version as of 21:50, 5 July 2013 (UTC) - Undid factually wrong edits by PhaseChanger". Could you clarify how the version you were replacing, [1] was incorrect? The version you placed, [2] appears to have the wrong geometry on the "front" carbons: according to the eye's position, the chlorine and methyl are up/down whereas the Newman has them side-to-side. DMacks (talk) 16:13, 14 May 2019 (UTC)

[3] by PhaseChanger had Cl in the back. So if the CIP-priority is Cl > CH3 > OH > CH3 (1 > 2 > 3 > 4). Priority numbering in the pic by PhaseChanger is wrong. If you fix the numbering, then at first look axial chirality is S. But you have to turn the molecule 180 degrees so that Cl is closer to the eye (ex). Then you'll realize it is in fact R, the same as in [4] by OgreBot. Newman projections in the pic by OgreBot should be rotated by 90 degrees to make it less confusing. Alternatively I think that the pic by PhaseChanger should be altered so that Cl (priority 1) is closer to the eye instead of OH (priority 3) so that the image is less confusing, but also the numbering should be changed. Keministi (talk) 04:54, 15 May 2019 (UTC)
The chemgapedia link says "first the substituents in front (a, b) and then separately the substituents at the back (c, d), regardless of whether the substituent b shows a lower CIP priority than substituent c." The CIP-priority is Cl > CH3 > OH > CH3 (1 > 2 > 3 > 4) if it were a single tetrahedral center, but it's not. The rule seems to say that instead, OH > CH3 (1 > 2) because they are in the front then Cl > CH3 (3 > 4) in the back. DMacks (talk) 06:21, 15 May 2019 (UTC)
I missed that sentence, but I think that statement is problematic. If it is regardless, you could the rotate the molecule 180 degrees. Then e.g. c and d switch places in the Newman projection and what was previously of R-chirality is then of S-chirality... and the whole concept of axial chirality is subjective. IUPAC Goldbook definition with its pictures is of no help as axial chirality of a molecule like abC=C=Cab can not be defined. abC=C=Ccd is mentioned in the IUPAC definition, but it is not discussed further – is there any official way to define the chirality of a molecule like abC=C=Ccd or the one in this picture we are discussing about? I don't know? Keministi (talk) 18:32, 15 May 2019 (UTC)
Looking "from the other end" does not change the R/S. The front is still "1 and 2" (in normal CIP order between them) and the back is "3 and 4" (in normal CIP order between them). It doesn't matter how the front vs back atoms relate to each other in CIP terms. doi:10.1002/anie.200462661 is the formal spec of the M/P nomenclature, and it states that explicitly (see Figure 4), and likewise states the same situation in aR/aS (footnote 36). abC=C=Cab is most definitely chiral (File:Allene chirality.png. this chemgapedia page is a more complete one than the one you mentioned earlier, with rotatable molecules to see the (non-)effect of looking at either end. DMacks (talk) 02:07, 17 May 2019 (UTC)
I'm convinced of my mistake. Sorry about that. Let's switch the pic back to the one made by PhaseChanger. Keministi (talk) 04:26, 17 May 2019 (UTC)
No worries. Thanks for checking back into it. DMacks (talk) 02:57, 20 May 2019 (UTC)
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