Question

Assign an \(R\) or \(S\) configuration to the chiral center in each molecule.

Short answer

Answer: To determine the R or S configuration of a chiral center in a molecule based on the CIP rules, follow these steps: (1) Identify the chiral center, (2) Assign priorities to the attached groups, (3) Arrange the groups in decreasing order of priority, and (4) Observe the arrangement of groups to find the configuration (R if clockwise, S if counterclockwise).

Step-by-step solution

Identify the chiral center

First, identify the chiral center(s) in the molecule. Chiral centers are carbon atoms bonded to four different groups or substituents.

Assign priorities according to CIP rules

Using the Cahn-Ingold-Prelog (CIP) priority rules, assign priorities to the four different groups attached to the chiral center. The priority is based on the atomic number of the atom that is directly connected to the chiral center. If there is a tie (atoms with the same atomic number), move one step away from the chiral center and compare the next set of atoms in the groups.

Arrange the groups in decreasing order of priority

Visualize the molecule in a way that the lowest priority group (usually hydrogen) is pointing away from you or is in the "back" position (dotted line). Arrange the remaining groups in a circle around the chiral center, so that they are in decreasing order of priority (1-2-3).

Determine the configuration (R or S)

Observe the arrangement of the groups in the circle from Step 3. If the sequence of groups goes clockwise, the configuration is R (rectus). If the sequence is counterclockwise, the configuration is S (sinister). After these steps have been followed and applied to each chiral center in the given molecule(s), you will successfully have determined the R or S configuration for those chiral centers.