I'm struggling to assign a stereodescriptor for the C8 position of the molecule. Both ChemDraw and ACDlabs give me 8R as a result. But if we draw the simplified hierarchial diagraph according to last UIPAC recommendations (https://iupac.qmul.ac.uk/BlueBook/P9.html#9103) for this chiral center it's not that clear to me that C7 precedes C9, it looks rather the opposite to me. And I couldn't find any relevant example in the recommendations. Does anyone else have counterarguments against 8R?
It' 8R, because 6 bonds with O, while 10 only bonds with C and H. Therefore, 7 precedes 9.
Yes, I see that. However in order to compare lower branches (C7-C6-... and C9-C10-...) we have to make sure that the upper branches (C7-O-1'-... and C9-O-1-...) do not allows us to make the decision. We are looking at the upper branches at the beginning because they contain O atom in the second sphere. But it's not clear to me if the upper branches are useless or not to make the decision about the priority. They seem very similar, but not exactly. Of course if the upper branches are considered equal it would be much easier to make the decision according to the priority of the branches below.
I'm trying to follow the IUPAC 2013 recommendations. But this example seems borderline unless I'm misinterpreting some rules.
Well, I don't see any troubles here. If the lower branches don't give you an answer, you have to consider the higher branches.
In other words: C[7]H(OC[1']...)(C[6]HO...) precedes C[9]H(OC[1]...)(C[12]H2...], because in the former residue there is C[6]-O, while there is no O on C[12].
In the end, you have to compare whole residues.
- Badges
- Science topic
- Similar topics
- Papers