Topic: Absolute configuration on 2 biphenyls (Read 4767 times)

Lithium · « **on:** July 23, 2008, 02:26:37 PM »

Can you have absolute configuration on a biphenyl? If so how do decided the R and S I have a Cl going up on the top and a Cl going down on the other.

azmanam · « **Reply #1 on:** July 23, 2008, 03:21:08 PM »

not unless there's atropisomerism. Wedges and hashes (if they're directly attached to the aromatic ring) are meaningless, because they're sp2 carbons.

R and S are not the right identifiers. I think for atropisomers, the identifiers are P and M, but I don't remember the rules off hand. + and - also work.

http://www.cem.msu.edu/~reusch/VirtTxtJml/sterism3.htm#isom19b
http://en.wikipedia.org/wiki/Atropisomerism

azmanam · « **Reply #2 on:** July 23, 2008, 03:44:33 PM »

see attached for what I have in my notes from 1st semester organic in grad school. (it's for allenes, but the analysis is the same for any bond of hindered rotation)

http://en.wikipedia.org/wiki/Axial_chirality
http://en.wikipedia.org/wiki/Allenes
http://goldbook.iupac.org/A00547.html