Organic Chemistry: Stereochemistry

What is the definition of a chiral center (stereocenter) in a molecule?

A tetrahedral carbon atom that is bonded to four different groups or atoms.

Define enantiomers and their relationship to each other.

Enantiomers are stereoisomers that are non-superimposable mirror images of each other.

What is a racemic mixture, and what is its net optical activity?

A racemic mixture is an equimolar (50:50) mixture of two enantiomers; it has zero net optical activity.

What two criteria must a molecule meet to be classified as a meso compound?

It must contain two or more chiral centers and possess an internal plane of symmetry, making it achiral.

How does an achiral molecule interact with plane-polarized light?

It does not rotate the plane of polarized light and is considered optically inactive.

According to the 2^n rule, what is the maximum number of stereoisomers for a molecule with 3 chiral centers?

The maximum number of stereoisomers is 8 (2 to the power of 3).

In the Cahn-Ingold-Prelog (CIP) system, how is priority assigned to atoms attached to a chiral center?

Priority is assigned based on decreasing atomic number; the higher the atomic number, the higher the priority.

If the lowest priority group (4) is pointing toward the viewer (on a wedge), how do you determine the R/S configuration?

Determine the sequence 1→2→3 and then reverse the result (clockwise becomes S, counter-clockwise becomes R).

What is the stereochemical relationship between (2R, 3R)-tartaric acid and (2S, 3S)-tartaric acid?

They are enantiomers because the configuration at every chiral center is inverted.

What is the stereochemical relationship between (2R, 3R)-2,3-dibromobutane and (2R, 3S)-2,3-dibromobutane?

They are diastereomers because they are non-mirror image stereoisomers with at least one, but not all, centers inverted.