How Do We Designate the Configuration of a Stereocenter

Identify the stereocenter in each and draw stereorepresentations of the enantiomers of each. 

You will find it helpful to study models of each pair of enantiomers and to view them from different perspectives. As you work with these models, notice that each enantiomer has a carbon atom bonded to four different groups, which makes the molecule chiral. Translate what you see in each model by using perspective drawings. The hydrogen at the stereocenter is shown in (a) but not in (b). 

When locating stereocenters, it is often helpful to draw in the hydrogens in line-angle drawings. Carbon atoms with only one or two lines extending from them, as well as sp and sp hybridized carbons, can be excluded from consideration. Once the stereocenters are identified, use dashed and solid wedges to show the bonds to substituents. 

Because enantiomers are different compounds, each must have a different name. The over-the-counter drug ibuprofen, for example, shows enantiomerism and can exist as the pair of enantiomers shown here  

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