How To Find Chiral Centers (Stereocenters) In Cholesterol

Label the eight chiral centers in cholesterol. How many stereoisomers are possible for a molecule with this many chiral centers?

A chiral center is a carbon with four different groups. We must first show all the hydrogens on all the carbons in the cholesterol molecule. Since each carbon always wants 4 bonds, we know how many hydrogens to add. For example, a carbon with 3 bonds has one hydrogen.

Once all the hydrogens have been added, we know that carbons with 2 or 3 hydrogens can not be chiral centers because they can not have 4 different groups.
Next we look at carbons with one hydrogen or no hydrogens. We must go atom by atom until the first point of difference to identify different groups and check whether the carbon is chiral or not.

To find the number of possible stereoisomers, we simply use the formula 2^n where n is the number of chiral centers.

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