What is the configuration (R or S) of these molecules?

AI Thread Summary
The discussion centers on determining the stereochemistry of two molecules, specifically identifying them as R or S configurations. The initial confusion arose from incorrectly prioritizing functional groups, with COOH mistakenly given higher priority than NH2 in the first molecule. In the second molecule, the error involved not switching from R to S due to overlooking the priority of a carbon atom over a hydrogen atom in the chain. Participants clarify that the correct priority must consider all substituents attached to the stereocenter, emphasizing the importance of accurately assigning priorities based on the C atoms involved. A request is made to redraw the molecule for better understanding, highlighting the need for visual aids in complex stereochemical discussions.
sd34
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Hi. Can someone tell me which molecule is R or S?

For me, the first one is S and the second one is R.
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I think the first is R and the second is S.

Can you explain how you arrived at your answers?
 
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mjc123 said:
I think the first is R and the second is S.

Can you explain how you arrived at your answers?

Yes, it’s correct.

Basically the mistake I made was that I gave the first priority to COOH instead of NH2 in the first molecule, whereas in the second one I forgot to switch from R to S.
 
Okay, I have another doubt.

Why the carbon on the right is S and not R?

Aren’t the priorities like this?
 

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You've forgotten the other C atom on the C 2 atoms from the stereocentre on the chain you labelled 2.
 
mjc123 said:
You've forgotten the other C atom on the C 2 atoms from the stereocentre on the chain you labelled 2.

Okay, but isn’t the priority still the same?
 
No, that C trumps the H on C2 on the other chain.
 
mjc123 said:
No, that C trumps the H on C2 on the other chain.

If it’s not too much of a trouble, could you redraw the molecule?
 
molecule.png
 
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mjc123 said:

Thanks a lot! So basically I switched no.1 and no.2 in terms of priority.
 
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