Tips for Stereochemistry

1. When drawing asymmetric carbon centers...

Let's Practice: Circle all structures that are properly drawn. For those that are improper, explain why.

2. When drawing multiple stereoisomers of a compound...

Let's Practice: Below are eight stereoisomers of the same compound as above (hydrogens have been omitted for simplicity). Determine which structures are identical.

a. Each carbon can have a maximum of one wedge bond and one dash bond coming from it.

b. If one of the four substituents is a hydrogen, then it is acceptable to only have a wedge or a dash, with the rest of the bonds drawn in a "trigonal planer" fashion. If only three bonds are drawn in to a stereocenter (plus one implied hydrogen), then two in-plane (non-wedge/dash) bonds must be used.

c. If none of the substituents are hydrogen, then the carbon must have a wedge and a dash bond.

d. If an atom has both a wedge and a dash bond to it, they MUST be next to each other.

e. Bonds connecting stereocenters should be drawn in-plane (not as a wedge/dash bond).

a. It is usually easiest to draw all of the bonds in the same place for all structures and alter the stereochemistry by switching the substituents that are on the wedge and the dash.

Example:

b. Check for identical structures by labeling each center as "R" or "S" in each stereoisomer. For two stereoisomers, if R/S configuration is retained at each stereocenter, then the two compounds are identical. If R/S configuration is opposite at all stereocenters, then the compounds are enantiomers. If R/S configuration is retained at some stereocenters, but reversed at others, then the two compounds are diastereomers. This is why it is best to draw all the bonds in the same place for each structure, because then it is easiest to tell which stereocenters have switched from R to S or S to R.

HClH

ClH

Br

ClH

ClH

Br

ClOH

HO H Cl H HO H H Cl H OH Cl H H OH H Cl

HO

Cl OH OH Cl

OH

Cl

OH

ClCl

ClOHOH Cl

Cl

OH

Created by Hanna KeyGrinnell College