Know what is meant by chiral and how it relates to nonsuperimposable objects and isomers

1. Know what is meant by chiral and how it relates to nonsuperimposable objects and isomers • Objects that are not superposable on their mirror images are chiral (from the Greek: cheir, hand). • They show handedness. • The most common cause of chirality in organic molecules is the presence of a carbon with four different groups bonded to it. • A carbon with four different groups bonded to it is called a stereocenter.

4. How to identify molecules with stereo carbons • *Straight Chain alkanes • *Cycloalkanes

5. Because stereoisomers are different compounds, each must have a different name. • Here are the stereoisomersof the over-the-counter drug ibuprofen. • The R,S system is a way to distinguish between sterioisomers without having to draw them and point to one or the other.

6. How to specify stereo centers: the R & S system • The first step in assigning an R or S configuration to a stereocenter is to arrange the groups on the stereocenter in order of priority. • Priority is based on atomic number. • The higher the atomic number, the higher the priority. • Use the next table as a guide

8. To assign an R or S configuration: 1. Assign a priority from 1 (highest) to 4 (lowest) to each group bonded to the stereocenter. 2. Orient the molecule in space so that the group of lowest priority (4) is directed away from you; the three groups of higher priority (1-3) then project toward you. 3. Read the three groups projecting toward you in order from highest (1) to lowest (3) priority. 4. If reading the groups 1-2-3 is clockwise, the configuration is R; if reading them is counterclockwise, the configuration is S.