7.8 Optical Activity

7.8 Optical Activity

• Determine the configuration of every stereocenter for each compound.
• The COOH group is a carboxylic acid group.

• A mirror image of a compound with an enantiomer.
• When you subject a compound to plane-polarized light, it's interesting.
• As the sample passes through the plane of the light, it rotates.
• We say the rotation is + if it is clockwise.
• If the rotation is counterclockwise, we say so.
• If we want to refer to a racemic mixture as an equal mixture of both enantiomers, we will often say (+/-) in the beginning of the name to mean that both enantiomers are present in solution.

• When determining configurations, do not confuse clockwise rotation of plane-polarized light with clockwise ordering of atomic numbers.
• A set of man-made rules is imposed when determining configuration.

• The rotation of plane-polarized light is not a man-made convention.
• It is measured in the lab.
• It is not possible to predict whether a compound will be + or - without actually going into the lab and trying.
• The temperature will determine whether a compound is + or -.

• A compound can be + at one temperature and - at another.
• They are not related.

• Unless you know how the enantiomer rotates plane-polarized light, you will never be expected to look at a compound that you have never seen and predict which direction it will go.