Chiral molecules R or S

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

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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

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