Help Sheet

To Assign the R and S Configuration

1. Draw in all the atoms around the stereocenter

2. Assign priorities (a,b,c,d).

3. Draw structure so that the lowest priority atom (d)is in the back. (With rings this is normally
just a flip.)

4. Draw an arrow from highest priority to lowest priority (a to c), if the arrow you draw goes
clockwise (to the right) than it is R,if it goes counterclockwise (to the left) it is S.

See next pages for examples.

Rings

Br

Cl

Assign the configuration of the carbon with the Cl attached.

Step 1

Step 2

Step 3

Step 4

Acyclic Molecules

Br

H

CH3

H

H

CH3

Assign the configuration of the carbon with the Br attached.

Step 1- Already done

Step 2

Br

H

CH3

H

H

CH3

a

b

c

d

Step 3

Step 4

CH3

Br

H

H

H

CH3

a

b

c

Arrow drawn counterclockwise therefore S