Final answer:
To determine the correct R or S configuration of a stereocenter, assign priority to the groups based on atomic number, orient the molecule so the lowest priority group is away, and trace a path from highest to lowest priority. If the path is clockwise and #4 is away, the configuration is R; if counterclockwise, it's S. If #4 was not away initially, reverse the assignment.
Step-by-step explanation:
To assign the correct R or S designation for the stereocenter carbon atom in a molecule, you need to follow a specific process involving the Cahn-Ingold-Prelog priority rules. First, assign priorities to the four groups attached to the chiral center based on the atomic number of the atoms directly attached to the carbon. The group with the atom of the highest atomic number gets priority #1, and so on, until the group with the atom of the lowest atomic number gets priority #4. You then orient the molecule so that the group with the lowest priority (#4) is pointing away from you. If this is not possible due to the type of projection used, you may need to swap the position of groups in your analysis mentally or physically (by redrawing the molecule).
Once priority #4 is pointing away, trace a path from priority #1 to priority #2, then to priority #3. If the path is clockwise, the configuration is R; if counterclockwise, it is S. However, if #4 was not originally pointing away, you must reverse this assignment (i.e., if you swapped positions, a clockwise path would mean S and counterclockwise would mean R).
For example, if you are given a chiral center with groups -Br, -NH₂, -CH₃, and -H attached to it with priority order -Br > -NH₂ > -CH₃ > -H, and -H is on the hashed wedge, pointing away, and the path from #1 to #2 to #3 is counterclockwise, then the stereocenter is assigned an S configuration.