How Do I Determine (S) vs. (R) Configuration in Cyclopentanediol?

In summary, this question asks me to name this molecule which has an OH on the 1st carbon and a S on the 2nd carbon. The attempted solution is confusing because it is unclear how to determine which of the two possible structures is being depicted.
  • #1
Chiborino
21
0

Homework Statement


15qpwsl.jpg

A question on a pretest asks me to name this. I know it's either (1R,2R) or (1S,2S)1,2-Cyclopentanediol because the OH's are facing in opposite directions, but I'm not sure how to figure out if the OH's are S or R



2. The attempt at a solution
I somewhat have an understanding of the concept, but I'm not entirely sure how to do it with a ring structure.

To be more specific, I'm confused about how to set up the determination of S vs. R. I know I can draw the top carbon either one of these two ways:
308xfsw.jpg

I'm just not sure about how to figure out which one is actually what's being depicted
 
Last edited:
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  • #2
15qpwsl.jpg

Since the carbon atoms are all depicted in the same plane, the c-c bonds also lie within the same plane. That means that of the two remaining bonds on each carbon atom, one is projecting toward the viewer (dark wedge or invisible H) and the other is projecting away from the viewer (dashed wedge or invisible H). This should be sufficient for you to construct a model.

308xfsw.jpg


Remember that in this representation, the vertical bonds are actually projecting away from the viewer, and the horizontal bonds are projecting toward the viewer.

If you're trying to visualize this rather than using an actual model, think of rolling the molecule away from you until you're looking at it edge-on, with the carbon formerly at the top now pointing away from you. The carbon at the top of the ring is now on the far side of the molecule, the C-C bonds point to the left and right (but the rotation moves them from "down" to "toward me"), the C-H bond points down and away, and the C-O bond points up and away.
 
Last edited:
  • #3
PhaseShifter said:
15qpwsl.jpg

Since the carbon atoms are all depicted in the same plane, the c-c bonds also lie within the same plane. That means that of the two remaining bonds on each carbon atom, one is projecting toward the viewer (dark wedge or invisible H) and the other is projecting away from the viewer (dashed wedge or invisible H). This should be sufficient for you to construct a model.




308xfsw.jpg


Remember that in this representation, the vertical bonds are actually projecting away from the viewer, and the horizontal bonds are projecting toward the viewer.

If you're trying to visualize this rather than using an actual model, think of rolling the molecule away from you until you're looking at it edge-on, with the carbon formerly at the top now pointing away from you. The carbon at the top of the ring is now on the far side of the molecule, the C-C bonds point to the left and right (but the rotation moves them from "down" to "toward me"), the C-H bond points down and away, and the C-O bond points up and away.

So then, rolling it away from me would put the OH on top, and that would mean that it's the (1R,2R)-1,2-cyclopentanediol.

Thanks alot. :D
 

1. What is the difference between (S) and (R) configurations in Organic Chemistry?

The (S) and (R) configurations refer to the spatial arrangement of atoms around a chiral carbon in a molecule. (S) indicates a counterclockwise rotation of the molecule, while (R) indicates a clockwise rotation. This is determined by the priority of the atoms attached to the chiral carbon, with the highest priority group being placed in the back and the lowest priority group in the front for (S) and the opposite for (R).

2. How is the (S) or (R) configuration determined in a molecule?

The (S) or (R) configuration is determined using the Cahn-Ingold-Prelog (CIP) priority rules. These rules assign priority to the atoms attached to the chiral carbon based on the atomic number of the atoms bonded to it. The molecule is then rotated so that the lowest priority group is in the back, and the configuration is determined by the direction of the remaining groups.

3. Are (S) and (R) configurations interchangeable?

No, (S) and (R) configurations are not interchangeable. They represent two different spatial arrangements of atoms around a chiral carbon and cannot be converted into one another without breaking the chemical bonds.

4. What is the significance of (S) and (R) configurations in Organic Chemistry?

The (S) and (R) configurations are important in Organic Chemistry because they help to determine the physical and chemical properties of a molecule. They also play a crucial role in the synthesis and reactions of chiral compounds.

5. Can (S) and (R) configurations change over time?

No, (S) and (R) configurations do not change over time. They are fixed for a specific molecule and can only be changed through chemical reactions or manipulations in the laboratory.

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