Question

Label each stereogenic center in the following compounds as R or S.

a) CH₃CHBrCl
b) CHFClBr
c) CH₃CHOHCH₃
d) CH₃CH(OH)CH₂Cl

Answer 1

To label the stereogenic centers as R or S, one must assign priorities based on atomic number, visualize the 3D arrangement, and determine the path direction. However, without concrete spatial information or views, we cannot accurately assign R or S to the compounds listed.

Step-by-step explanation:

The stereogenic centers in a molecule are those where the attachment of different groups creates a chiral center, leading to non-superimposable mirror images or enantiomers. To determine whether a center is R or S, we assign priorities to the attached groups based on atomic number, and then we visualize the arrangement of these groups in three-dimensional space.

Here's how you determine the configuration:

1. Assign priorities based on the atomic number of atoms directly attached to the chiral center, with the highest atomic number being #1 and the lowest being #4.
2. Orient the molecule so that the group with the lowest priority (usually a hydrogen) is pointing away from you.
3. Trace a path from the highest priority (1) to the next highest (2), and then to the next (3). If the path is clockwise, the center is R; if counterclockwise, it is S.
4. If the lowest priority group is not pointing away from you, perform a mental rotation after determining R or S, and then switch the assignment.

Let's apply this to the compounds listed:

• CH3CHBrCl: This molecule does not have a stereogenic center because it lacks four different groups attached to any single carbon.
• CHFClBr: This has a tetrahedral carbon with four different groups, so it is a chiral center. Assigning priorities: Br(1) > Cl(2) > F(3) > H(4). Depending on the orientation, determine the R or S configuration.
• CH3CHOHCH3: This molecule does not have a chiral center because both sides of the hydroxyl (-OH) group are CH3 groups, making them identical.
• CH3CH(OH)CH2Cl: This contains a chiral center at the carbon with the -OH group. Assign priorities, consider the 3D arrangement, and determine the R or S configuration.

Note that without knowing the spatial arrangement of the substituents, we can't assign R or S configurations to certain compounds in 2D or using their formula alone.