Identify each of the following pairs of Fischer projections as enantiomers or identical compounds:
a.

Verified step by step guidance

1. Examine the Fischer projections carefully. Fischer projections are a two-dimensional representation of molecules, where horizontal lines represent bonds projecting out of the plane (toward the viewer), and vertical lines represent bonds projecting into the plane (away from the viewer).
2. Identify the chiral centers in each molecule. A chiral center is a carbon atom bonded to four different groups. Note the arrangement of the groups around each chiral center in both Fischer projections.
3. Compare the configurations (R or S) of the chiral centers in the two Fischer projections. To determine the configuration, assign priorities to the groups attached to the chiral center based on the Cahn-Ingold-Prelog priority rules, then determine the direction of the priority sequence (clockwise for R, counterclockwise for S).
4. If the configurations of all chiral centers are opposite (e.g., R becomes S and S becomes R), the molecules are enantiomers. If the configurations are identical, the molecules are identical compounds.
5. Verify your conclusion by checking if one Fischer projection can be rotated or flipped to match the other. Remember, enantiomers are non-superimposable mirror images, while identical compounds are superimposable.

Key Concepts

Fischer Projections

Fischer projections are a two-dimensional representation of three-dimensional organic molecules, particularly useful for depicting stereochemistry. In these diagrams, vertical lines represent bonds that project away from the viewer, while horizontal lines represent bonds that project towards the viewer. This format is commonly used to illustrate carbohydrates and amino acids, allowing for easy identification of stereoisomers.

Enantiomers

Enantiomers are a type of stereoisomer that are non-superimposable mirror images of each other. They typically arise in molecules that contain one or more chiral centers, where the arrangement of atoms around the chiral center leads to two distinct configurations. Enantiomers often exhibit different optical activities, meaning they rotate plane-polarized light in opposite directions, which is a key characteristic used to distinguish them.

Identical Compounds

Identical compounds refer to molecules that have the same molecular formula and structural arrangement, resulting in the same physical and chemical properties. In the context of Fischer projections, two compounds are considered identical if they can be superimposed on one another without any changes in orientation. Identifying identical compounds is crucial in stereochemistry, as it helps differentiate between enantiomers and other types of isomers.