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Can pseudochirality be considered when three or four groups on the carbon atom are constitutionally the same, but configurationally different?

For example, when the C atom is bonded to one H, and then three more structurally identical groups with 2 chiral C each - in configurations R,R and S,S and R,S respectively - then by assigning each of the 4 groups a priority value (since they are all different - though 3 have the same structure) we can assign a configuration to this C atom.

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  • $\begingroup$ See this earlier answer and also follow the link describing "prochirality". That web page also discusses proprochirality. If that doesn't answer your question, post back with a bit more detail in your question (in these cases a drawing of the molecule would be very helpful) $\endgroup$ – ron Apr 20 '15 at 15:37
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Ah, now I think I understand what you're asking. You're saying that we have a central carbon to which is attached a hydrogen and 3 groups with the same structure. Each of these 3 groups contains 2 chiral carbons. One group is R,R one is R,S and one is S,S.

So yes, the chirality of the central carbon (it is chiral, it is not meso or prochiral - there is no plane of symmetry bisecting the central carbon) can be assigned using the Cahn–Ingold–Prelog priority rules where "R" has higher priority than "S". Therefore the priority ranking around the central carbon in your molecule would be R,R > R,S > S,S > H.

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  • $\begingroup$ Yes, that's exactly what I meant. Although I think this carbon cannot rotate light in its path, and isn't optically active - I think its configuration will be designated using symbols r and s rather than R and S. $\endgroup$ – Charles Apr 21 '15 at 15:22
  • $\begingroup$ Your molecule is chiral, there is no symmetry element present. It will rotate the plane of polarized light.. The enantiomer would be R,R S,R S,S. R and S will still be used to denote the configurations at the 6 chiral carbons. r and s are only used with prochiral carbons (see my link in my comment up above). There are no prochiral carbons in your molecule. $\endgroup$ – ron Apr 21 '15 at 15:26
  • $\begingroup$ Oh - a C which has H, OH, and a group in R, R and R, S configurations (the group has 2 chiral C) attached is optically active? A non superimposable mirror image does form about this C - the configurations of the groups attached become S,S and R,S. $\endgroup$ – Charles Apr 24 '15 at 15:56
  • $\begingroup$ "a compound in which a C has H, OH, and a group ", what is the fourth group attached to C? $\endgroup$ – ron Apr 24 '15 at 15:58

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