What is the configuration of each of the following?
a.
b.

Verified step by step guidance

1. Step 1: Identify the chiral center in each molecule. A chiral center is a carbon atom bonded to four different groups. In both molecules (a and b), the central carbon atom is the chiral center.
2. Step 2: Assign priorities to the substituents attached to the chiral center based on the Cahn-Ingold-Prelog (CIP) priority rules. The priority is determined by the atomic number of the atoms directly attached to the chiral center. For molecule (a), the groups are OH, CH3, H, and CH2OH. For molecule (b), the groups are OH, CH2CH3, H, and CH2OH.
3. Step 3: Orient the molecule so that the lowest priority group (H) is pointing away from you. This is typically done by imagining the molecule in a 3D perspective or using a model.
4. Step 4: Determine the order of the remaining three groups (1, 2, 3) in a clockwise or counterclockwise direction. If the order is clockwise, the configuration is R. If the order is counterclockwise, the configuration is S.
5. Step 5: Repeat the process for both molecules (a and b) to determine their respective configurations. Ensure you carefully follow the CIP rules and visualize the molecule in 3D to assign the correct configuration.

Key Concepts

Chirality

Chirality refers to the geometric property of a molecule that makes it non-superimposable on its mirror image. A chiral molecule typically has a carbon atom bonded to four different substituents, leading to two distinct configurations known as enantiomers. Understanding chirality is crucial for determining the configuration of molecules in organic chemistry.

Fischer Projections

Fischer projections are a two-dimensional representation of three-dimensional organic molecules, particularly useful for depicting stereochemistry. In these projections, vertical lines represent bonds that extend away from the viewer, while horizontal lines represent bonds that come towards the viewer. This format helps in visualizing the spatial arrangement of substituents around chiral centers.

Stereocenters

Stereocenters, or chiral centers, are atoms in a molecule that have four different substituents attached, leading to different spatial arrangements. The configuration of these centers can be designated as R (rectus) or S (sinister) based on the Cahn-Ingold-Prelog priority rules. Identifying stereocenters is essential for determining the overall stereochemistry of a compound.