How do you assign R/S configuration in organic chemistry?

Assign priorities by atomic number, place the lowest-priority group pointing away, then trace the order of the remaining groups: clockwise is R and counterclockwise is S.

Think of the chiral center as a little compass with four arms where each arm holds a different group, and first you look at the atom directly attached to the center and rank those atoms by their atomic numbers so larger atomic numbers get higher priority, and if two attached atoms are the same you move outward along the chain until a difference appears; then you orient the molecule so the lowest-priority group is pointing away from you, and finally you look at the path from the highest-priority group to the next and then the next one, and if that path goes around like a clock it is R but if it goes the other way it is S, and remember that double or triple bonds are treated by imagining the multiple bonds as if the atom were bonded to duplicate or triplicate phantom atoms so you can compare correctly.

Common mistakes include forgetting to orient the lowest-priority group away, which can flip R to S or S to R so always redraw or mentally rotate the molecule so the lowest group is on a dashed wedge or pointing back; another error is misranking atoms when you encounter identical immediate atoms, so always compare the next set of atoms out along the chain as if you were listing three attached atoms for each substituent; and a third frequent mistake is mishandling double bonds, so remember to replace a double bond with two single bonds to phantom atoms for priority comparisons and then proceed with the normal rules.

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Assigning R/S Configuration in Organic Chemistry

1. Rank atoms by atomic number
2. Compare outward when tied
3. Orient lowest-priority group away
4. Trace highest-to-lowest priority path
5. Clockwise means R, counterclockwise S
6. Treat multiple bonds as duplicates

Common R/S Assignment Mistakes

1. Forgetting to orient lowest-priority group away
2. Misranking atoms when immediate atoms tie
3. Mishandling double bonds in comparisons

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