Final answer:
The R or S configuration of an asymmetric atom in a compound is determined by assigning priorities to the substituents of the chiral center and observing their spatial arrangement. The configuration is R if the sequence is clockwise and S if counterclockwise when the lowest priority substituent is pointing away; if not, the assignment is reversed.
Step-by-step explanation:
The asymmetric atom in a compound determines its chiral nature, and such an atom can have the R (rectus) or S (sinister) configuration, indicating its absolute configuration. To assign the R or S configuration, the four substituents of the chiral center must be assigned priority according to the Cahn-Ingold-Prelog priority rules. Number 1 is given to the highest priority substituent, and number 4 to the lowest.
Assigning R or S to the chiral center involves looking at the arrangement of these substituents. In situation where the lowest priority (number 4) substituent is pointing away from the viewer, the configuration is determined to be R if the sequence 1-2-3 is clockwise and S if counterclockwise. If the lowest priority substituent is not pointing away, the assignment must be reversed.
An sp³-hybridized atom with four different substituents attached will form two non-superimposable configurations, known as enantiomers. It is crucial to note that these configurations must be determined by the actual spatial arrangement and not merely by their optical activity, as a compound's dextrorotatory (+) or levorotatory (-) nature does not always correlate with its R or S configuration.