
406
S
Steric
substituents can exist in different stereoisomers, such a carbon is called
a chiral center. The original (and still one of the best) examples of stereo-
isomerism are the two forms of tartaric acid, discovered by Louis Pasteur.
It can be hard to see from a picture, so if you can, you should try to make
models of the two species as shown and you will discover that they are
not the same at all:
CH
3
CH
3
COOH
OH
HO
HOOC
H
H
Steric: Any effect that is caused simply by a chemical group physically
getting in the way, rather than by any particular properties of that group, is
called a steric effect. A good denition to keep in mind (