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

In summary, the conversation discusses a mistake made in assigning priorities to COOH and NH2 groups in two molecules, resulting in the incorrect identification of the first molecule as R and the second as S. The mistake was due to forgetting to switch from R to S in the second molecule and not considering a carbon atom on the C 2 chain. The conversation concludes with a request to redraw the molecule and a clarification on the priority of the C atom over the H atom on the C 2 chain.
  • #1
sd34
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TL;DR Summary
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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  • #2
I think the first is R and the second is S.

Can you explain how you arrived at your answers?
 
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  • #3
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.
 
  • #4
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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  • #5
You've forgotten the other C atom on the C 2 atoms from the stereocentre on the chain you labelled 2.
 
  • #6
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?
 
  • #7
No, that C trumps the H on C2 on the other chain.
 
  • #8
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?
 
  • #9
molecule.png
 
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  • #10
mjc123 said:

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

1. What is the configuration (R or S) of a molecule?

The configuration of a molecule refers to the spatial arrangement of its atoms. In organic chemistry, the R and S system is commonly used to describe the configuration of chiral molecules.

2. How is the configuration of a molecule determined?

The configuration of a molecule is determined by the relative positions of its substituents. This is done by assigning priorities to the substituents based on the atomic number of the atoms attached to the chiral center and then visualizing the molecule in 3D space.

3. What is the difference between R and S configuration?

The R and S configuration are two different ways to describe the spatial arrangement of a chiral molecule. R configuration refers to a clockwise arrangement of substituents around the chiral center, while S configuration refers to a counterclockwise arrangement.

4. Can a molecule have both R and S configurations?

No, a molecule can only have one configuration at a given chiral center. This is because the substituents are fixed in their positions and cannot rotate freely to switch between R and S configurations.

5. Why is it important to know the configuration of a molecule?

The configuration of a molecule is important because it affects its physical and chemical properties. Enantiomers, which have opposite configurations, can have different biological activities, and knowing the configuration of a molecule is crucial in drug development and understanding biochemical processes.

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