stereochemistry with examples.PDF

Stereochemistry

•  Some objects are not the same as their mirror

images (technically, they have no plane of

symmetry)

–  A right-hand glove is different than a left-hand

glove

–  The property is commonly called “handedness”

•  Organic molecules (including many drugs) have

handedness that results from substitution

patterns on sp 3 hybridized carbon

Enantiomers – Mirror Images

•  Molecules exist as three-dimensional objects

•  Some molecules are the same as their mirror

image

•  Some molecules are different than their mirror

image

–  These are stereoisomers called enantiomers

Why is this important?

• Our bodies, for example, can only create and

digest carbohydrates and amino acids of a

certain stereochemistry

• All of our proteins that make up our hair, skin,

organs, brain, and tissues, are composed of a

single stereoisomer of amino acids

• Our bodies can make and digest starch

(found in potatoes and bread)

• Our bodies cannot digest cellulose (found in

wood and plant fibers), even though both are

just polymers of glucose of different

stereochemistry

Shown above: Only one stereoisomer of Ibuprofin

has the correct three-dimensional shape to bind to

the receptor, so only one isomer actively relieves

pain.

Enantiomers and the Tetrahedral

Carbon

•  Enantiomers are molecules that are not the

same as their mirror image

•  They are the “same” if the positions of the

atoms can coincide on a one-to-one basis (we

test if they are superimposable , which is

imaginary)

•  This is illustrated by enantiomers of lactic acid