Chiral molecules R or S

Stereocentres are assigned configuration (labelled R or S) according to well defined rules Cahn–Ingold–Prelog (CIP).

Background Colour:

Click the structures and reaction arrows to view the 3D models and animations respectively

Step 1
Assign the atoms numbers 1 to 4 based on highest atomic number. In this example nitrogen has the highest atomic number and is assigned 1 whereas hydrogen has the lowest atomic number and is assigned 4
Step 2
Arrange the molecule so that the lowest priority substituent faces backwards in this case number 4
Step 3
Mentally move from substituent 1 to 2 to 3. If you are moving clockwise assign the label R. If anticlockwise assign the label S

S as anticlockwise

Next example

Back to stereochemistry home