This makes an excellent organic
chemistry lecture demonstration. Spartan is coded to recognize the absolute
configuration at tetrahedral carbons. Don't expect perfection, but the
program usually does a great job. Note that labels only appear in the
wire or ball&wire models. Before you begin, go to the model menu
and configure labels to show chirality. Turn labels on.
Build 4-methylheptane so that it is easy to see the plane of symmetry.
No R or S label should appear on your screen. Now place a halogen at
position 1. You should immediately see an R or S appear next to your
stereocenter. Assign the ligand priorities to confirm the assignment.
Now place the same halogen at the opposite end and see this label disappear
as the structure becomes achiral again. Try adding another substituent
anywhere on the chain and two labels appear as stereocenters are created.
Work through the concepts of substituent placement, atomic number, etc.
You can do a lot with this simple approach. Fisher projections can be
modeled by creating an eclipsed ethane model and then adding substituents.
Cyclic structures pose many interesting examples. For example cis-1,3-dimethylcyclohexane
is a MESO compound and both labels will appear even though this structure