How To Determine R and S Configuration On Chiral Centers

In this video, we learn how assign R/S configuration on a chiral center.

1. Find a chiral carbon (stereocenter) = carbon connected to 4 different groups.

2. Assign priorities 1-4 to atoms attached to the carbon where 1 is the biggest atomic number and 4 is the smallest atomic number. Draw in hydrogen whenever necessary (if a carbon is shown with only 3 bonds).

3. If atoms are the same, you must continue going atom by atom until the first difference. Do not look at the group as a whole.

4. If group 4 is dashed, then connect 1 through 3 and determine the direction. Clockwise (R- to the right), counterclockwise is S.

5. Count a double bond as if the atom were connected to two other atoms and similarly for the triple bond.

6.What to do if the number 4 is not on a dash? TRICK!

Switch the number 4 with whatever group is on the dash. Determine stereochemistry with the new numbers, and then say the OPPOSITE stereochemistry.

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