R- and S- nomenclature of chirality centers

In the simplest and most common case, a chirality center is characterized by an atom that has four different groups bonded to it in such a manner (e.g. tetrahedral) that it has a non-superimposable mirror image.

       Assigning R and S Configurations With the Cahn-Ingold-Prelog (CIP) Rules

• Identify each of the chirality centers.
• Assign the priority (1 to 4) to each group attached to the chirality center
• 
  
  
  

If the two atoms have same atomic number then highest atomic weight atom will be the highest 

priority group or atom.

e.g. (D>H)